Article

# Reproductive characteristics of the ocean leatherjacket, Nelusetta ayraudi

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## Abstract

The ocean leatherjacket (Nelusetta ayraudi) is one of the largest members of the family Monacanthidae. Distributed throughout inshore waters around the southern half of Australia, this schooling species supports substantial commercial and recreational fisheries. N. ayraudi do not conform to either of the general reproductive modes reported within the family, but exhibit characteristics of both strong social reproductive behaviour and of being promiscuous and polygynous. Sexual dimorphism, with males and females exhibiting differing colouration and body shapes, and ripe ovaries being an order of magnitude larger than ripe testes, are characteristic of social reproductive behaviour and pair spawning. In contrast, high batch fecundity (mean of 320 oocytes per gram of body weight), similar sizes and ages at sexual maturity (350 mm and 2.5 years respectively) and the formation of large spawning aggregations in offshore waters are characteristic of being promiscuous and polygynous. Similar to many other coastal marine species off the east and west coasts of Australia, N. ayraudi are partial spawners during the austral winter months with spawning restricted to the part of their distribution that is towards the upper area of the prevailing currents. It is hypothesized that N. ayraudi off eastern Australia have evolved a life-history strategy whereby fish move northwards through time, spawning occurs in these more northern waters and the southerly flowing Eastern Australian Current facilitates dispersal of eggs and larvae southwards. The reproductive characteristics described provide various options to fishery managers who wish to enhance the sustainability of the fishery through increased egg production. These include spatial and temporal fishing closures to protect breeding fish during the spawning period, the protection of juveniles through either inshore area closures, improving the selectivity of fishing gears and/or regulated minimum legal lengths.

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... Globally, studies on reproduction and diet of monacanthids indicate enormous inter-species variability (Kawase & Nakazono, 1996). Research on their biology, worldwide, is limited to studies on a few species, mostly small, including Cantherhines pardalis (Rüppell, 1837) (Kawase & Nakazono, 1994), Monacanthus tomentosus (Linnaeus, 1758) (Peristiwady & Geistdoerfer, 1991), Stephanolepis hispidus (Linnaeus, 1766) (Mancera-Rodríguez & Castro-Hernández, 2015a, 2015b, Stephanolepis diaspros (Fraser-Brunner, 1940) (Zouari-Ktari et al., 2008El-Ganainy & Sabrah, 2013), Thamnaconus modestus (Günther, 1877) (Kim et al., 2013), Nelusetta ayraudi (Quoy & Gaimard, 1824) (Miller & Stewart, 2013) and Meuschenia scaber (Forster, 1801) (Visconti et al., 2018a(Visconti et al., , 2018b. ...
... During monsoon, due to inclement weather conditions and sea state, the shallow and inshore waters are trawled extensively, whereas during other seasons, weather conditions and sea state are favourable, and trawling is carried out offshore in deeper waters. It is likely that the larger individuals inhabit the deeper waters and the smaller individuals dwell in the shallower waters, as observed for other monacanthids, such as Meuschenia scaber (Visconti et al., 2020), Stephanolepis hispidus (Mancera-Rodríguez & Castro-Hernández, 2015a) and Nelusetta ayruadii (Miller & Stewart, 2013). The majority of the individuals caught along western Bay of Bengal were from depths <100 m, with few landed from beyond, and the maximum inhabiting depth recorded was 124 m. ...
... Mean and modal TL was higher in females than in males, indicating higher growth rate in females. Growth rate variations between sexes have been reported earlier for other monacanthids (Kawase & Nakazono, 1994;El-Ganainy & Sabrah, 2013;Miller & Stewart, 2013;Mancera-Rodríguez & Castro-Hernández, 2015a;Visconti et al., 2018b). Negative allometric growth with individuals growing more quickly in length than in weight was observed for A. monoceros, in contrast to other monacanthid species, for which growth is mostly isometric ( Table 6). ...
Article
No prior comprehensive information on the reproductive biology and trophodynamics of Aluterus monoceros was globally available. The present study was performed on 1036 individuals landed along the western Bay of Bengal during 2017 to 2019. Length ranged between 25.3–64.4 cm in females (mean at 48.34 cm) and from 21.5–64.1 cm in males (mean at 47.83 cm). Growth was negatively allometric with no significant difference between sexes. Sex ratio (F:M) was 1.03 with variations based on sizes and months. Size at sexual maturity for females and males was 40.85 and 41.60 cm, respectively. The species spawned throughout the year with major and minor peaks during February to May and October and November. Absolute fecundity increased linearly with length and weight and ranged from 33,640 eggs to 12,39,202 eggs. Stomachs were empty or with trace amounts of food in 59.17%, part-full in 34.07% and full in 6.76% of the fishes. Stomach vacuity and fullness and predator–prey weight ratios varied with an increase in body size, implying higher feeding intensity in large-sized fishes. Feeding activity was more intense during June–August and less during the peak spawning months. The species is omnivorous and a bottom feeder. Teleosts contributed the most to the prey items (43.23% by Index of Preponderance) implying preference for carnivory. Ontogenetic shifts and seasonal variations in prey items were observed. The present study provides paramount information that can significantly contribute to the management and conservation of monacanthid stocks in northern Indian Ocean.
... The reproductive biology of monacanthids has been little studied, despite a long history of exploitation and increased fisheries attention in various parts of the world in the last two decades (FAO 2006). The information currently available is limited to a few species, including the toothbrush leatherjacket Penicipelta vittiger (Castelnau, 1873) and the southern leatherjacket Meuschenia australis (Donovan, 1824) from Tasmanian waters (Barrett 1995b), the lessepsian reticulated leatherjacket Stephanolepis diaspros (Fraser-Brunner, 1940) of the Gulf of Gabes (Rim & Mohamed-Nejmeddine 2011), the ocean leatherjacket Nelusetta ayraudi (Quoy & Gaimard, 1824) in south-eastern Australia (Miller & Stewart 2013), and the planehead filefish Stephanolepis hispidus (L. 1766) of the Canary Islands (Mancera-Rodríguez & Castro-Hernández 2015). ...
... After capture each fish was measured to the nearest mm (total length L T ; standard length L S and body depth BD), and total weight (W T ) and gutted weight (W G ) were recorded to the nearest 10 g. Sex was confirmed upon dissection, and each gonad assigned a macroscopic stage of reproductive development following the scheme of Miller and Stewart (2013) for the monacanthid N. ayraudi. Each gonad was then photographed (Figure 3), weighed to the nearest 0.01 g, and stored in FAAC, a formalin-based fixative (Pears et al. 2006), for a period no longer than six months before histological processing. ...
... All gonad sections were observed using a Leica DMRE upright microscope equipped with a colour camera (Leica DC500), and digital images were captured using AnalySIS LifeScience software. Microscopic developmental stages were assigned following Miller and Stewart (2013) and Lowerre-Barbieri et al. (2011), with minor adjustment to fit M. scaber gonad characteristics. ...
Article
Full-text available
The leatherjacket Meuschenia scaber is widely distributed in Australasian waters, and is a valued bycatch of inshore bottom trawl fisheries although little is known of its life history. Here, we describe the reproductive biology of the species based on 651 leatherjackets sampled in the Hauraki Gulf, New Zealand, between July 2014 and March 2016. The maximum total length (LT) recorded for females and males were 320 and 315 mm, respectively, with both sexes present in all size classes. Monthly analysis of gonad condition revealed a clear spawning season from late austral winter to early summer (August–December), and histological analysis of the ovaries revealed that M. scaber is an indeterminate serial spawning gonochorist. The estimated sizes at sexual maturity (L50) for females (189.9 mm LT) and males (188.4 mm LT) did not differ significantly. Relatively small testes, sexual dimorphism and underwater observation of nesting suggest that M. scaber is a paired spawner.
... All species spawn adhesive demersal eggs on a variety of structures, show parental egg care, and have pelagic larvae (e.g., Nakazono and Kawase 1993;Kawase and Nakazono 1994a;Kawase 2005Kawase , 2008. Other species exhibit characteristics of strong social reproductive behavior including being promiscuous and polygynous with broadcast spawning in offshore waters and not showing parental egg care (Miller and Stewart 2013). Studies have been conducted on the spawning period, sex ratio, mean size at sexual maturity (L 50 ) and fecundity (Nakamura 1942;Ishida and Tanaka 1983;Barlow 1987;Nakazono and Kawase 1993;Kawase and Nakazono 1994aZouari-Ktari and Bradai 2011;El-Ganainy and Sabrah 2013). ...
... A major objective for adequate management of a fishery is to know the reproductive biology of the fish, including the spawning timing, recruitment and mean length or age of a species at which these events occur, because it is important to establish strategies for preservation of the stock (Miller and Stewart 2013). The fishing regulations in the Canary Islands waters do not limit the S. hispidus catch, despite the overfishing. ...
... Zouari-Ktari and Bradai (2011) reported an absolute fecundity that oscillated between 28,250 and 218,000 oocytes in S. diaspros in Tunisian waters. Miller and Stewart (2013) found that, in Australian waters, the absolute fecundity of Nelusetta ayraudi ranged between 84,234 and 892,468 oocytes and mentioned that it was similar to that reported for T. modestus (210,000-1,460,000 oocytes). It is important to highlight that we report the number of oocytes found in the gonads and all of them will probably not be spawned. ...
Article
Full-text available
The reproductive biology of the planehead filefish, Stephanolepis hispidus, in the waters of the Canary Islands area was studied. The study was conducted with a sample of 906 specimens from 8.9 to 25.9 cm in total length (TL) that were caught in fish traps from February 1998 to August 1999. Females predominated in the catches, and the sex ratio of 1.0:1.4 significantly deviated from the theoretical 1:1 distribution. This ratio varied when calculated by the length classes and by the season. Based on the monthly evolution of the Gonadosomatic Index (GSI) and the proportion of mature individuals, the spawning season occurred between May and October, with a peak in July and August for both sexes. This species accumulates energy reserves in the liver to be spent during the maturation of the gonads and spawning. The mean size at sexual maturity (L50) was 13.9 cm TL in females and 14.9 cm TL in males. The fecundity of S. hispidus fluctuated between 14,071 and 91,323 (mean = 55,239 ± 19,079), and the relative fecundity oscillated between 460 and 1,238 oocytes/g of eviscerated weight (mean = 904 ± 206). The diameter of the oocytes was 0.47 mm (SD = 0.10). The described reproductive characteristics provide options to fishery managers including regulations for spatial and temporal fishing closures to protect the breeding fish during spawning and the selectivity of fishing gears. Thus, it is proposed that fishing be limited to water depths greater than 30 m and that the minimum legal length of fish be established at 18 cm TL.
... These changes may be due to recruitment variability. Ocean Jackets are a short-lived species, living for up to 6 years and maturing at around 2.5 years (Miller and Stewart, 2013). The population has, therefore, the potential to fluctuate greatly depending on the strength of individual year classes. ...
Article
We examined spatial and temporal variations in the demersal fish assemblage on the continental shelf of the central Great Australian Bight to understand how the assemblage is affected by both fishing and environmental gradients. Data from the Great Australian Bight Trawl Sector (1988–2018) and fishery-independent trawl surveys (2005–2009, 2011, 2015, 2018) were used for the analyses. The independent survey data were used to analyse trends in overall species composition and abundances, while the commercial fishery data were used to extend the time series for the key commercial species, Deepwater Flathead (Platycephalus conatus) and Bight Redfish (Centroberyx gerrardi). The demersal fish assemblage was dominated by four commercial species: Deepwater Flathead, Bight Redfish, Ocean Jacket (Nelusetta ayraud), and Latchet (Pterygotrigla polyommata); and one by-catch species: Wide Stingaree (Urolophus expansus). Assemblage composition varied between day/night and along an east-west gradient. Survey abundance and commercial catch-per-unit-effort of several species declined at the end of the time series. Survey abundance was low in 2011, 2015, and 2018 for Bight Redfish and in 2015 and 2018 for Deepwater Flathead. Assemblage composition and catch rates of some species recorded in 2011, 2015, and 2018 were distinct from previous years, but the differences appear to reflect the longer gaps between these surveys and the combined effects of historical fishing pressure and environmental variability. Recent downward trends in the abundance indices of target species, as well as long-term changes in the assemblage, demonstrate the need for continued fishery-independent monitoring. The relative importance of fishing pressure, environmental variability, and other human activities in driving these changes warrant further investigation.
... Chrysophrys auratus (Forster 1801) and Nelusetta ayraudi (Quoy & Gaimard 1824) (Mackie et al., 2009;Miller & Stewart, 2013). ...
Article
Scorpaeniformes are an important component of commercial and recreational fisheries world-wide. The Neosebastes species, found in the western Pacific and south-east Indian Ocean, have received little attention from a research perspective. Samples of the bighead gurnard perch, Neosebastes pandus, collected from the lower west and south coasts of Western Australia, were used to undertake the first comprehensive investigation of the biological characteristics of a Neosebastes species. Opaque zones in sectioned sagittal otoliths were validated as forming annually. Female N. pandus grow to a significantly larger size, on average, than males and dominate the largest size classes, while males, growing to a smaller size, accumulate in the intermediate size classes. Although males were far less numerous than females in those age classes in which both sexes were found, males and females attain similar maximum ages > 25 years. Neosebastes pandus spawns over a brief period between May (austral late autumn) and July (austral mid-autumn) when water temperature and day length are declining. The mean monthly GSI (IGS ) values of females during the spawning period are 37-50 times higher than that of males, which mature at an earlier age and smaller length compared to females. Histological examination of the ovaries of females indicate that their structure is consistent with 'general' teleost ovarian anatomy and thus differs from Scorpaena, Helicolenus and Sebastes species whose ovaries are adapted for specialised reproductive modes. The reproductive strategy of N. pandus of maximising the reproductive output of females, by this sex attaining a larger size than males, and pair spawning (i.e. large disparity in IGS values), demonstrate the close lineage between the Neosebastes and other Scorpaeniformes, such as the Scorpaena, Helicolenus and Sebastes.
... The various aspects of the life history traits especially reproductive tactics (size at first maturity, sex-ratio, spawning season and fecundity) of threatened freshwater fishes is important for sustainable fisheries management as well conservation of their natural stocks (Angermeier, 1995;Helfman, Bruce, Dougales, & Bowen, 2009;Nikolsky, 1969). These studies are essentially meant for elucidating both short-term and long-term variations in the production of broods which are finally recruited in the population as exploitation stocks (Miller & Stewart, 2013). No exhaustive information available on the reproductive characteristic of H. thomassi. ...
Article
The study provides new information on the reproductive biology of Hypselobarbus thomassi (Day, 1874) an endemic cyprinid fish in the Western Ghats–a biodiversity hotspot of India. A total of 384 specimens (males = 244 and females = 140) were collected monthly from April 2009 to March 2011 from Kallada River of Southern part of Western Ghats, India. Monthly sex ratio indicated that males predominated in the fishery, and an overall sex ratio was significantly different from the expected value of 1:1 (male:female = 1:0.57, x2 = 28.17, p < .01). Based on the monthly analysis of gonadosomatic index (GSI) and the proportion of mature individuals, the spawning season of H. thomassi occurred between May to October with a peak in June to August. The length at first maturity (L50) recorded was 290 mm TL in males and 330 mm TL in females. The absolute fecundity ranged between 305 (234 mm TL) to 1,089 (414 mm TL) and relative fecundity oscillated between 77.3–220.69 oocytes/g of fish. The fecundity established a linear relationship with total length, body weight and ovary weight. The findings of this study would be very effective to impose sustainable conservation plan for this threatened species in Kallada River and other Western Ghats river systems.
... Despite enormous diversity and wider distribution, the group is relatively less studied in terms of species-specific life-history traits, reproductive biology, and ecological roles. The studies were limited to a countable number of species from scattered locations (Mancera-Rodríguez and Castro-Hernández 2004;Miller and Stewart 2013;Kim et al. 2016;Visconti et al. 2017Visconti et al. , 2018. Monacanthids do not form commercial fishery along the Northwestern coastal states of India barring Aluterus monoceros (Linnaeus, 1758) which has emerged as an important fishery along Gujarat coast. ...
Article
Full-text available
Fishes of family Monacanthidae, popularly known as filefishes are a specialized group of fishes with low commercial importance in the studied region barring Aluterus monoceros, which has emerged as commercial fish in the region in last few years. Three species, namely Aluterus scriptus, Stephanolepis diaspros, and Stephanolepis auratus, have been reported for the first time from the region, adding to the monacanthid diversity of the region. Morphometric assessment of the four species revealed several discriminating attributes capable of separating the species from each other.
... This period of peak spawning centred on the months of summer also corresponds with the highest average water velocities recorded for the EAC (Ridgway and Dunn 2003), which aids the transport and dispersal of larvae spawned by the Bfecundity reserve^(sensu Venturelli et al. 2010) of large old A. trutta in northern NSW south to the main nursery areas in Tasmania and Victoria (Malcolm 1966b;Nicholls 1973;Stanley and Malcolm 1977). A progressive northward migration with increasing age is a commonly reported life-history strategy for both coastal marine invertebrates (e.g., Montgomery 1990;Stewart and Kennelly 1998) and teleosts (e.g., Gray et al. 2012;Miller and Stewart 2012;Stocks et al. 2014) in SE Australia, which utilise the southward-flowing EAC to deliver early life history stages to higher latitudes. ...
Article
Full-text available
Knowledge of the influence of both spatial and temporal environmental gradients on life history traits and population demographics is a critical requirement in the management of exploited fish populations. This study examined variation in the demographics of Arripis trutta, an economically-important pelagic fish species with a broad latitudinal distribution in the waters of coastal south-eastern (SE) Australia, a region dominated by the influence of the East Australian Current (EAC). A validated ageing protocol was first developed using sectioned sagittal otoliths, which in turn permitted examination of latitudinal variation in A. trutta growth, size compositions and age compositions. The von Bertalanffy growth function parameters for A. trutta in SE Australia were estimated to be L∞ = 63.20 ± 0.37 cm fork length (FL), k = 0.26 ± 0.01 yr⁻¹ and to = −0.14 ± 0.03 yr, with a maximum estimated age of 12.7 years. Growth was shown to be faster with decreasing latitude likely due to a simple relationship with the latitudinal gradient in water temperature; fastest growth occurring in northern NSW and slowest growth occurring in Tasmania. Latitudinal patterns in growth were remarkably similar to those previously reported for this species, despite age being estimated using scale readings some 40 years ago. This consistency in latitudinal growth patterns of a temperate fish can be attributed to the life history-related movements undertaken by A. trutta in this region. This temporally-consistent movement pattern is supported by the spatial gradient in the size and age composition of A. trutta sampled from different latitudes in both the current and historical research, whereby numbers of large and old fish increase progressively from Tasmania to northern NSW. These results highlight the need to consider the potential for spatial size- or age-structuring in the development of sampling designs and interpretation of results for any study examining spatial or temporal variation in demographic parameters of exploited fish populations.
... Spawning-related migrations to specific areas where there are currents that will transport larvae to suitable nursery habitat have been documented for multiple fish species in Australia (Ward et al. 2003;Miller and Stewart 2013), Africa (Beckley and Hewitson 1994;Beckley and Connell 1996), and North America (Hare and Cowen 1993;McBride and McKown 2000). Gilmore (2001) found a similar migration-larval dispersal pattern for Common Snook in the IRL, where fish migrated 1 south (e.g., from 28 00 0 N to 27 00 0 N) to spawn in nearshore waters, allowing larvae to recruit northward along the coast. ...
Article
A population's fidelity to spawning sites and variation in the strength of site fidelity among individuals are influential components of fish population dynamics. The literature on fidelity to aggregation sites is dominated by studies on marine species, whereas less is known about the fidelity of euryhaline species to spawning aggregation sites. We used passive acoustic telemetry to quantify intra-annual and interannual site fidelity and resident habitat associated with spawning sites (inlets) for 280 sexually mature Common Snook Centropomus undecimalis through an array of more than 200 receivers deployed in rivers, estuaries, inlets, and nearshore waters along 320 km of Florida's Atlantic coast. Fish were detected four times as often at and made twice as many trips to a primary spawning inlet than to secondary inlet sites. Fish displayed interannual site fidelity, returning to the primary inlet for as many as five consecutive reproductive seasons. Overall, individuals returned to their primary inlet (return rate [RR] = 0.54) more often than they changed sites between years (straying rate [SR] = 0.29), but variation in RRs and SRs between inlets suggested a spatial effect on interannual site fidelity. During the nonspawning season, fish generally resided less than 40 km to the northwest of their primary inlet. The 95% kernel density estimates (KDEs) for catchment area and dispersal area averaged 220 km2 and overlapped greatly for five out of six inlets. The 50% KDE did not overlap between inlets, suggesting that each spawning site had a corresponding winter resident habitat supporting a group of fish that were primarily associated with that inlet. The inclusion of telemetry data in traditional measures of site fidelity allowed for the identification and accurate description of behavioral polymorphism and may be applied to other fish species when spatial substructuring is suspected. Received June 9, 2015; accepted December 3, 2015
... The presence of exclusively mature G. elevata individuals within the north of the species distribution suggests the potential migration of a portion of the population to the north (Stocks et al. 2014a, in press). This may be a larval dispersal strategy utilised by several south-eastern Australian invertebrates (Montgomery 1990;Stewart and Kennelly 1998) and teleosts (Stewart et al. 2011;Gray et al. 2012;Miller and Stewart 2013) that use the strong southward moving East Australian Current to deliver larvae to increased latitudes. Further studies examining the movement patterns throughout the species latitudinal distribution would provide more information on latitudinal interactions and connectivity between populations. ...
Article
Characterising the movement and habitat affinities of fish is a fundamental component in understanding the functioning of marine ecosystems. A comprehensive array of acoustic receivers was deployed at two near-shore coastal sites in southeastern Australia, to examine the movements, activity-space size and residency of a temperate rocky-reef, herbivorous species Girella elevata. Twenty-four G. elevata individuals were internally tagged with pressure-sensing acoustic transmitters across these two arrays and monitored for up to 550 days. An existing network of coastal receivers was used to examine large-scale movement patterns. Individuals exhibited varying residency, but all had small activity-space sizes within the arrays. The species utilised shallow rocky-reef habitat, displaying unimodal or bimodal patterns in depth use. A positive correlation was observed between wind speed and the detection depth of fish, with fish being likely to move to deeper water to escape periods of adverse conditions. Detection frequency data, corrected using sentinel tags, generally illustrated diurnal behaviour. Patterns of habitat usage, residency and spatial utilisation highlighted the susceptibility of G. elevata to recreational fishing pressure. The results from the present study will further contribute to the spatial information required in the zoning of effective marine protected areas, and our understanding of temperate reef fish ecology.
... The presence of exclusively mature G. elevata within the northern region may suggest the northern migration of a proportion of the population. Northern migration with ontogenetic development is common life-history strategy of coastal south-east Australian marine invertebrates (Montgomery, 1990;Stewart & Kennelly, 1998) and teleosts (Stewart et al., 2011;Miller & Stewart, 2013) that utilize the southward-flowing EAC to deliver larvae to higher latitudes (Gray et al., 2012). Further studies of the early life stages of larvae, including mechanisms of dispersal, as well as genetic analyses and otolith microchemistry are required for assessing population connectivity and the utility of larval seeding from marine protected areas (Christie et al., 2010). ...
Article
Latitudinal variation in the reproductive characteristics of a temperate marine herbivore, rock blackfish Girella elevata, was examined from three regions of the south-eastern Australian coast. Biological sampling covered 780 km of coastline, including the majority of the species distribution. The sampling range incorporated three distinct oceanographic regions of the East Australian Current, a poleward-flowing western boundary current of the Southern Pacific Gyre and climate-change hotspot. Girella elevata are a highly fecund, group synchronous (multiple batch)-spawner. Mean fork length (LF ) and age at maturity were greater for females than males within all regions, with both male and female G. elevata of the southern region maturing at a greater size and age than those from the central region. Estimates of batch fecundity (FB ) were greatest in the northern and southern regions, relative to the central region where growth rates were greatest. Significant positive relationships were observed between FB and LF , and FB and total fish mass. Gonado-somatic indices indicated latitudinal synchrony in spawning seasonality between G. elevata at higher latitudes, spawning in the late austral spring and summer. A late or prolonged spawning period is evident for G. elevata from the northern region. Juvenile recruitment to intertidal rock pools within the central and southern regions was synchronous with the spawning season, however, no juveniles were found within the northern region. The implications of latitudinal variation in reproductive characteristics are discussed in the context of climate and oceanographic conditions of south-east Australia. © 2015 The Fisheries Society of the British Isles.
... Spawning-related migrations to specific areas where there are currents that will transport larvae to suitable nursery habitat have been documented for multiple fish species in Australia (Ward et al. 2003;Miller and Stewart 2013), Africa (Beckley and Hewitson 1994;Beckley and Connell 1996), and North America (Hare and Cowen 1993;McBride and McKown 2000). Gilmore (2001) found a similar migration-larval dispersal pattern for Common Snook in the IRL, where fish migrated 1 south (e.g., from 28 00 0 N to 27 00 0 N) to spawn in nearshore waters, allowing larvae to recruit northward along the coast. ...
Article
In general, snook Centropomus spp. are opportunistic carnivores, feeding on fish and crustaceans, as shown by other studies on diets of centropomids in the western Atlantic Ocean. Diet studies for centropomids in Florida refer only to a description of the diet and the ontogenetic shifts in prey preferences of Common Snook C. undecimalis. However, no food habit information for Smallscale Fat Snook C. parallelus is available in Florida. Stomach content analysis and quantitative descriptions of fish diet are important in understanding how species utilize resources, coexist in certain habitats, and possibly share available prey. The objective of this study was to describe the dietary composition for Smallscale Fat Snook in east-central Florida, in comparison to other diet studies for Smallscale Fat Snook and its congeners. The results show that, like other snook species, Smallscale Fat Snook is a carnivorous species, juveniles feed mainly on penaeid shrimp, and larger fish feed more on varied prey, mainly portunid crabs and teleost species. The diverse diet composition of Smallscale Fat Snook in east-central Florida suggests that the species is an opportunistic feeder, exploiting locally abundant prey, and feeds in a variety of estuarine and riverine habitats. Received March 18, 2014; accepted April 17, 2014
... Potential explanations for the absence of smaller fish include: poor recruitment during years prior to sampling, sampling biases, southward larval drift within the EAC and/or the migration of a proportion of the population to the north. The northern migration with ontogenetic development is a common life-history strategy of coastal south-east Australian marine invertebrates (Montgomery, 1990;Stewart and Kennelly, 1998) and teleosts (Gray et al., 2012;Miller and Stewart, 2012;Stewart et al., 2011) that utilise the southward flowing EAC to deliver larvae to higher latitudes (Gray et al., 2012). Further studies examining otolith chemistry, larval drift and genetic analyses may shed light on the life-history of this enigmatic northern population. ...
Article
Trawling is generally an unselective fishing method that is employed to harvest a number of species. Capture of nontarget species that are subsequently discarded is an important issue for trawl fisheries, especially penaeid trawl fisheries. While gear modifications are a common approach to manage this issue, maintaining areas that are closed to trawling may also have a positive impact on these nontarget species. This study systematically examined the diversity and abundance of nontarget species across a network of areas closed to trawling (trawl closure areas) relative to adjacent areas that were open to trawling. Analysis of nontarget species from 209 trawls and 72,787 animals (across 216 taxa) revealed some impact on both abundance and diversity within trawl closure areas. Latitude was a key variable that was driving differences in the taxonomic assemblage among locations. Within locations, there were inconsistent impacts for different nontarget species in trawl closure areas. Length distributions showed size truncation of abundant nontarget species in fished areas relative to adjacent trawl closure areas. While the impact of trawl closure areas varied among species, it was clear that the spatial management in the fishery provided some refuge for a diversity of nontarget species, observed in patterns of species richness, abundance, and population size structure. Latitudinal breadth appears to be an essential component of the trawl closure network, but localized effects may be important for maintaining reproductive capacity for nontarget species. These data highlight the broader utility of trawl closure networks as a management tool for trawl fisheries.
Article
Current pearl grafting techniques were developed in the early 1900s and have changed little since. They involve the sacrifice of donor pearl oysters to provide graft tissue (saibo) that is implanted into host oysters. This study assessed the feasibility of using regenerated graft tissue for pearl production in the 'black-lip' pearl oyster, Pinctada margaritifera. Twelve days after grafting with regenerated graft tissue, there was complete encapsulation of the nucleus by the fully developed pearl-sac and the first layer of organic matrix had been secreted. Sixteen days after grafting, the pearl-sac was completely integrated with host tissue. The epithelial cells in the pearl-sac continued to secrete the organic matrix layer but there were no signs of nacre deposition at this stage. However, after three months of culture, nuclei in oysters grafted with regenerated mantle tissue were completely covered with nacre. The average nacre thickness on pearls produced from regenerated (0.547 ± 0.01 mm, n = 8) and normal (0.532 ± 0.01 mm, n = 8) mantle tissue did not differ significantly (p > 0.05). Nacre secretion rates, over the 80 day period subsequent to pearl-sac formation were 6.84 ± 0.1 μm day(-1) and 6.66 ± 0.1 μm day(-1) for oysters grafted with regenerated and normal mantle tissue, respectively. These means were not significantly different (p = 0.258). Our results clearly show that regenerated mantle tissue can function successfully as saibo for pearl production in P. margaritifera. This finding could provide significant benefits to pearl farmers and provide a basis for further development of current pearl grafting practices. Copyright © 2015. Published by Elsevier Ltd.
Article
Appropriate development of the pearl-sac in pearl oysters is an important factor influencing the quality of cultured pearls. In this study, a total of 110 black-lip pearl oysters (Pinctada margaritifera) with a mean (± SE) antero-posterior measurement of 110.82 ± 0.41 mm and dorso-ventral measurement of 112.06 ± 0.45 mm were grafted to allow histological examination and chronological description of pearl-sac development in this species. Beginning 2 days after grafting, oysters were sacrificed regularly until the 48th day and the pearl-sacs of sampled oysters were sectioned and examined. Graft tissue proliferated and developed into a complete pearl-sac within 14 days of grafting when the epithelial cells responsible for nacre secretion were fully developed. However, first nacre secretion onto the nucleus was not observed until 32 days after grafting. The presence and accumulation of haemocytes in the pearl pouch initially and in the pearl-sac thereafter is one of the primary factors potentially affecting pearl quality. Clumps of haemocytes present between the pearl-sac and nucleus caused distension of the pearl-sac from an ideally spherical shape. Furthermore, the presence of byssus in close proximity to the developing pearl-sac was demonstrated in this study. This has the potential to impact pearl-sac formation and resulting pearl quality. The findings reported in this paper provide a more detailed understanding of pearl-sac development in P. margaritifera and a basis for future research towards developing improved pearl culture practices and pearl quality.
Article
The grafting process used for pearl production in pearl oysters triggers a significant haemocyte response which has an influence on the quality of pearls formed. One hundred and ten selected healthy adult Pinctada margaritifera were grafted for pearl production. Beginning two days after grafting, oysters were sacrificed regularly until the 48th day and the pearl-sacs of sampled oysters were sectioned for histological analysis. The level of haemocytes present in the pearl-sacs decreased overtime with the samples from day 2 showing the highest levels. Haemocyte levels also varied between samples from a particular day. The exact cause(s) of varying levels of haemocyte accumulation during pearl-sac development in P. margaritifera is not known. However, it is reasonable to assume that haemocyte production is positively related to the degree of damage caused to host oyster tissues during the grafting procedure. While haemocytes have an important wound healing role in pearl oysters, excessive haemocyte presence may be detrimental to maximizing pearl quality.
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The reproductive biology of the planehead filefish, Stephanolepis hispidus, in the waters of the Canary Islands area was studied. The study was conducted with a sample of 906 specimens from 8.9 to 25.9 cm in total length (TL) that were caught in fish traps from February 1998 to August 1999. Females predominated in the catches, and the sex ratio of 1.0:1.4 significantly deviated from the theoretical 1:1 distribution. This ratio varied when calculated by the length classes and by the season. Based on the monthly evolution of the Gonadosomatic Index (GSI) and the proportion of mature individuals, the spawning season occurred between May and October, with a peak in July and August for both sexes. This species accumulates energy reserves in the liver to be spent during the maturation of the gonads and spawning. The mean size at sexual maturity (L50) was 13.9 cm TL in females and 14.9 cm TL in males. The fecundity of S. hispidus fluctuated between 14,071 and 91,323 (mean = 55,239 ± 19,079), and the relative fecundity oscillated between 460 and 1,238 oocytes/g of eviscerated weight (mean = 904 ± 206). The diameter of the oocytes was 0.47 mm (SD = 0.10). The described reproductive characteristics provide options to fishery managers including regulations for spatial and temporal fishing closures to protect the breeding fish during spawning and the selectivity of fishing gears. Thus, it is proposed that fishing be limited to water depths greater than 30 m and that the minimum legal length of fish be established at 18 cm TL.
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We investigated spawning dynamics of southern bluefin tuna, Thunnus maccoyii, using ovaries obtained from fish caught on the spawning ground in the northeast Indian Ocean and their main feeding grounds in the Southern Ocean between October 1992 and June 1995. Only sexually mature southern bluefin tuna were caught on the spawning ground. Fish were caught on the spawning ground in every month except July, although relative abundance was low from May to August. Peaks in abundance occured during October and February. Individuals do not spawn over the whole season and there is a turnover of fish on the spawning ground. The presence of oocytes in all stages of development and the absence of a hiatus in the oocyte size frequency distributions between unyolked and early yolked oocytes indicate that southern bluefin tuna have asynchronous oocyte development and indeterminate annual fecundity. The presence of either migratory nucleus or hydrated oocytes and postovulatory follicles in the ovaries of many females indicates that they are capable of multiple spawning. Based on the proportion of females with postovulatory follicles, females spawn on average every 1.1 days. The average spawning batch fecundity, estimated from counts of hydrated oocytes, was 6.0 million oocytes or 57 oocytes per gram of body weight.
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Size at age, growth rates, seasonality of spawning, and size at maturity were described for the silver sweep Scorpis lineolatus off the coast of New South Wales, Australia. Estimates of age were made by counting annual zones in sections of otoliths. The ageing technique was validated using young‐of‐the‐year fish, staining fish with tetracy‐cline, and by marginal increment analysis. Silver sweep exhibited extreme longevity with an observed maximum age of 54 years and more than 50% of the fishery being greater than 15 years old. Growth was rapid during the first few years before reaching sexual maturity at 2–3 years and at a length of c. 17 cm fork length, after which growth slowed dramatically. Silver sweep displayed a winter spawning period. The fishery is unusual in that despite heavy fishing pressure and rapidly declining catches the age structure of the catch suggests a population that has been subjected to minimal fishing mortality. It is proposed that the large declines in commercial landings may be the result of serial depletion on local reefs and that current landings are being taken from schools of fish that have" receiveddate="little fishing pressure historically.
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The demonstration by this study that the life cycle characteristics of the reef fish Nemadactylus valenciennesi differed markedly from those of other cheilodactylids led us to compare these differences and hypothesise on their evolutionary implications. The distribution, length and age compositions, growth and the length and age at maturity of N. valenciennesi in south-western Australian waters have been determined. The maximum age (21 years) of N. valenciennesi (maximum total length=984 mm) is far less than those of the much smaller Cheilodactylus fuscus, Nemadactylus macropterus (both similar to 40 years) and Cheilodactylus spectabilis (97 years). Yet N. valenciennesi, N. macropterus and C. spectabilis mature at a similar young age (3-7 years). While, on the basis of data for other species, all three species mature at lengths consistent with their asymptotic lengths, the last two species mature at a far earlier age than would be predicted from their long life spans. The early attainment of maturity by N. macropterus and C. spectabilis may reflect a response to high juvenile mortality or constrained adult growth, whereas their long life spans could reflect a response to variable recruitment in the past or compensation for limited annual reproductive output due to very constrained adult growth.
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The growth and reproductive biology of the commercially and recreationally important sparid fish, tarwhine (Rhabdosargus sarba), was examined from the coastal waters of New South Wales (NSW), south-eastern Australia. Previous research on this species in other parts of the world has yielded conflicting results concerning its growth and reproductive biology. Age estimates were made by counting opaque zones in otolith sections. The method was validated by marking the otoliths of captive fish with alizarin complexone, and also by marginal increment analyses using otoliths from wild-caught fish. Both sexes grew at a similar rate. Von Bertalanffy growth function parameters were: L ∞; ≤ 26.40 ± 0.40 cm fork length (FL), k ≤ 0.39 ± 0.02 year-1 and to ≤ -0.56 ± 0.09 years. The maximum estimated age was 16.5 years. Spawning occurred from May to August with a peak in July. Both sexes matured at a similar size (L50 ≤ 19.44 ± 0.15 cm FL), which was larger than the current minimum legal length in NSW. Ovotestes were identified in adult tarwhine and were confirmed by histological analyses. Results of this study provided evidence that tarwhine are likely to be rudimentary hermaphrodites in eastern Australia and are more similar in growth rate, maximum size/age, and reproductive biology to tarwhine from Western Australia than those from other parts of the world.
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Achoerodus viridis (Pisces : Labridae) was sampled over two years at Little Bay, NSW, Australia, and comparative material was taken from a site 4.5 km away at Cape Solander. Population structure and gonadal structure showed that A. viridis was protogynous and monandric (i.e. no primary males were found). Histological sections of male gonads showed a gonadal lumen, general ovarian lamellar form and multiple sperm ducts running longitudinally through the gonad wall. Males dominated the larger size and age classes, whereas females predominated in the smaller size and age classes. The sex ratio of mature fish and the whole population was biased in favour of females. Individuals at both sites matured as females at 1+-2+ years. Fish at Little Bay functioned as females at ages ranging from 8+ to 18+ years before changing sex at a size between 480 and 580 mm SL. Fish at Cape Solander may function as females for up to 18+' years and change sex between 500 and 520 mm SL. Spawning occurred between July and October (1991-93).
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Reproductive behavior of the threadsail filefishStephanolepis cirrhifer was studied at Kashiwajima, southern Shikoku, Japan. This species spawned in pairs on the sandy bottom, the eggs being scattered over an area of about 15 cm in diameter and attached to sand particles. After spawning, males departed immediately, while the females remained at the site to guard the eggs for a few minutes. Thereafter the eggs were left unguarded for three days until hatching. Females spawned only once daily, whereas males mated with multiple females in succession. The reproductive males established territories, in which 1–4 resident females defended smaller territories from each other. The harem size changed according to some ecological conditions, such as population density. Moreover, the males also mated with visiting non-resident females. Thus, the two alternative tactics of females resulted in two mating patterns, haremic polygyny and female visiting of male territories, in a single population ofS. cirrhifer.
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Arripis georgiana was collected from coastal waters in Western Australia and South Australia. The opaque zones on the otoliths were shown to be formed annually and thus their number could be used to age the individuals of this species. Although the catches of A. georgiana in south-western Australia, where spawning occurs, were dominated by the 0+ to 5+ age classes, they did contain females and males up to ten and nine years old, respectively. The von Bertalanffy growth parameters for the two sexes in this region differed significantly, with the asymptotic length (L∞) being significantly greater for females (262 mm) than for males (239 mm), whereas the reverse was true for the growth coefficient (k), i.e. 0.813 v. 0.992. The catches of A. georgiana eastwards of 121˚44′E on the south coast of Western Australia, where spawning does not occur, were dominated by the 0+ to 2+ age classes. The above data, when taken in conjunction with earlier tagging experiments and the marked decline that occurs in the number of 2+ fish in South Australia in summer, imply that, during this period, many two-year-old individuals of A. georgiana start migrating towards their spawning areas in south-western Australia.
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The present study investigated the reproductive biology of blue mackerel (Scomber australasicus) off southern and eastern Australia and assessed the suitability of the Daily Egg Production Method (DEPM) for future stock assessment. This analysis revealed that S. australasicus is a serial spawner with asynchronous oocyte development and indeterminate fecundity. S. australasicus spawns between November and April off southern Australia and between July and October off eastern Australia. In southern Australia, ∼50% of males and females were mature at 236.5 and 286.8 mm fork length (FL), respectively. Size at ∼50% maturity could not be estimated reliably for eastern Australia owing to the smaller proportion of mature fish in samples. Mean spawning frequencies ranged from 2 to 11 days off southern Australia. Batch fecundity was related to fish size and mean batch size was 69 894 ± 4361 oocytes per batch and 134 oocytes per g of weight. The timing and duration of the spawning season, size at maturity, spawning frequency and batch fecundity of S. australasicus off southern Australia were consistent with those of S. japonicus in the northern Pacific Ocean. The present study's estimates of adult reproductive parameters of S. australasicus off southern Australia were suitable for the application of the DEPM for estimating spawning biomass. Collecting representative samples of mature fish from waters off eastern Australia during the spawning season is a high priority for future stock assessment of this species.
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Nelusetta ayraudi (the ocean leatherjacket) is an endemic Australian monacanthid species distributed from North West Cape (Western Australia) south to southern Queensland. The commercial and recreational fisheries targeting Nelusetta ayraudi have expanded substantially along the coast of New South Wales (NSW) in recent years but there exists little biological information on which to base effective management of this growing fishery. World-wide, only a few studies have aged monacanthids. Of these, researchers have interpreted periodic increments in bony structures such as vertebrae and anterior dorsal spines in preference to those found in otoliths. In this study we estimated age of N. ayraudi by counting growth increments in sectioned otoliths. The periodicity of increment formation was validated using a vital stain, (oxy-tetracycline), injected into young-of-the-year fish. Growth was rapid especially as juveniles with N. ayraudi attaining approximately 220 mm after 1 year and 340 mm after 2 years. No differences in growth rates were detected between sexes or between fish captured at different latitudes (zones). The largest male (605 mm, Total Length—TL) and female (656 mm, TL) were both recorded from northern NSW, with both sexes attaining the maximum age of 6+ years from northern and southern NSW. The von Bertalanffy parameters describing growth for N. ayraudi were $${L_\infty }$$ = 591 mm (TL), k = 0.377 year−1 and t o = −0.247 years.
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Triggerfishes construct nests by excavating depressions in sand. Eggs are laid in an adhesive mass and anchored with rubble. A photograph of a newly-hatched embryo is included.
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Spawning behavior of the pygmy leatherjacket Brachaluteres jacksonianus was studied in southeastern Australia. Prespawning females thrust the snout repeatedly into spawning substrata, while males exhibited courtship display and nuzzled the female’s face. The females and males touched their abdomens in pairs and released gametes. No parental egg care was observed after spawning. Fertilized eggs measured 0.74 mm in diameter, and each clutch contained 50–191 eggs. The eggs were attached to filamentous red algae, which were found on the surface of the seagrass and other substrata. Reproductive ecology of B. jacksonianus is similar to that of congeneric Brachaluteres ulvarum, although selection of spawning substrata differed in two species.
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Reproductive ecology of the black reef leatherjacket, Eubalichthys bucephalus (Monacanthidae), was studied in temperate Australia. The fish lived in the same heterosexual pairs, and each pair shared a home range composed of rocky reefs and boulders where they reproduced and fed on sponges. Spawnings were conducted in pairs, and fertilized eggs were attached to the algae-like Bryozoa species. Reproductive ecology of E. bucephalus was compared to other pair swimming fishes and confamilial species, and ecological features were discussed.
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Juveniles less than 20mm total length (TL) were collected by hand beam trawl from July through October. Small-sized fish 30 to 50mm TL began to be recruited to the catch by boat seine from August through September. Although they showed annual fluctuation of pattern in the length frequency distribution, small-sized fish grew up to large-sized fish from 50 to 70mm TL in spring through summer of the next year. A negative relationship between population density and growth in weight was observed. The spawning season is estimated to extend from May through September judging from the seasonal change of a gonadsomatic index. Some small-sized fish recruitd in summer also had well developed gonads. The rate of group maturity for females at around the end of August or time of recruitment showed annual variation, and was lower in 1977 when population density was higher than in other years.
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The ocean leatherjacket (Nelusetta ayraudi) has a long history of commercial exploitation in New South Wales, Australia. Records of reported landings indicate that substantial peaks of between 600 and 900 tonnes per annum occurred during the 1920s and again during the 1950s. These peaks were followed by large declines, which suggest that this species is vulnerable to over-exploitation. In recent years from 2000/01 to 2006/07, annual commercial landings of ocean leatherjackets using oceanic demersal fish traps and demersal otter trawl have increased from 134 to 430 tonnes. Between 2003 and 2005 ocean leatherjackets in commercial landings ranged approximately between 22 and 65 cm in total length. Ocean leatherjackets were fully recruited to the fishery at two years of age, with the majority of the catch (83%) aged either two or three years. The instantaneous total mortality rate was estimated from an age-based catch curve as 1.1. Natural mortality was estimated as approximately 0.5, based on a maximum age of 6 years. Yield per recruit indicated that under current levels of exploitation the yield per recruit would be maximized at a length at first harvest of 35 cm in total length.
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Sexual dimorphism in the body form of some monaeanthid taxa is very pronounced. The female is usually deeper bodied with a more concave snout profile than the more streamlined male. In addition. the second dorsal and anal fins of the female are generally less elevated anteriorly than those of the male. These differenees are reflected in variations of the underlying bones and muscles, particularly those adjacent to the bases of the second dorsal and anal fins. These differences are described and the reasons for them discussed. Introduction Differences in morphology between males and females of many species in the family Monacanthidae, commonly known as leatherjackets and filefishes, have caused considerable confusion in the past. Some of these differences now are better known, especially those involving body colour and scale structures (e.g., Randall 1964; Hutchins 1977, 1986; Tyler 1980). However, one which has received less attention in the literature entails the overall shape of the fish. Males of numerous species are usually more elongate than females, and possess convex dorsal profiles to the head, as against a more concave profile in females (Figure I). These differences are further accentuated by the shape of the second dorsal and anal fins. The anterior portion of each fin often is prominently elevated in males, producing an elongate, swept-back lobe, whereas in females, these fins usually are much lower, the anterior fin rays someti mes bei ng only a little longer than the middle rays (Figure I). This has led some workers to recognise males and females of the same taxa as separate species (e.g., Fraser-Brunner 1941; Masuda et al. 1975; Hutchins 1977; Kotthaus 1979). This situation recently was explored in detail as part of a larger study on the morphology and phylogeny of the family (H utchins 1988); however, much of that investigation still remains unpublished. The purpose of the present paper, therefore, is to report on this sexual dimorphism, and show how it is related to hitherto unreported differences in osteology and musculature that appear to be unique to the family. Methods Specimens of 96 of the 97 species considered valid (Hutchins 1988) were examined using radiography, whole skeletons, and cleared and stained material. For the last-mentioned examination, specimens were prepared following the trypsin digestion method ofTaylor (1967). (The largest specimen cleared and stained was 105 mm SL). Where possible, the material examined for each species included adults of both sexes and unsexed juveniles.
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The small filefish, Rudarius ercodes, generally spawning from mid May to early October in the natural habitat, was exposed to various photoperiod and temperature regimes. These environmental effects on the gonad activity, regression and recrudescence were experimentally investigated based on the mechanism of reproductive cycle. Spawning season was initiated in the early spring with the gonad activated by long photoperiod(13L) and stimulated by compensatory temperature rising. Even when the gonad activated readily at the above critical daylength (12L to 13L)was kept back at the below if, it went on maturing. At the end of spawning period (mid September), since the shortening of daylength (12L) resulted in the gonad regression regardless of temperature, the short daylength might be related to the termination of spawning in situ. When the regressive gonad at the post spawning period was treated by the above 13L: condition, it could recrudesce and bring forth even spawning. From this fact, the feasible control of annual reproductive cycle of small filefish was recognized. But even in the long daylength, the temperature above was preventive of gonad maturation.
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The reproductive cycle of the small filefish, Rudarius ercodes was investigated based on the annual variations of gonadosomatic index(GSI) and hepatosomatic index(HSI) by electronic and photic microscophy. The specimens used were collected at the coastal area of Benden island, Sizuokagen, Japan, from September 1982 to August 1983. GSI began to increase from March, starting season of longer daylength and higher water temperature, and reached the maximum value between June and August. It began to decrease from September with the lowest value appearing between November and February without any evident variation. The annual variations of HSI were not distinct in male filefish and were negatively related to GSI in female : HSI decreased in the summer season when the ovary was getting mature and reached the maximum in the winter season when the ovary was getting retrogressive. The ovary consisted of a pair of saccular structure with numerous ovarian sacs branched toward the median cavity. Oogonia divided and proliferated along the germinal epithelium of the ovarian sac. Young oocytes with basophile cytoplasm showed several scattering nucleoli along the nuclear membrane. when the oocytes growing to about 300 , nuclear membrane to disappear with nucleus migrating toward the animal pole. The regions of protoplasm were extremely confined within the animal hemisphere in which most of cytoplasms were filled with yolk materials and oil drops. After ovulation, residual follicles and growing oocytes remaining in the ovarian sacs degenerated. But perinucleatic young oocytes without follicles formed were not degenerated, and growing continuously still in the next year. Mitochondria and endoplasmic reticula in the cytoplasm remarkably increased with oocytes maturing and yolk accumulating. Those were considered to be functionally related to the yolk accumulation. Five or six layers of possible vitellogenin, oval-shaped disc structures with high electron density, appeared in the apex of follicular processes stretching to the microvilli pits of mature oocytes. Testis consisting of a pair of lobular structures in the right and left were united in the posterior seminal vesicle, Cortex of testis was composed of several seminiferous tubules, and medulla consisting of many sperm ducts connected with tubules. Steroid hormone-secreting cells with numerous endoplasmic reticula and large mitochondria of well developed cristae were recognized in the interstitial cells of the growing testis. Axial filament of spermatozoon invaginated deeply in the central cavity of the nucleus and the head formed U-shape with acrosome severely lacking, mitochondria formed large globular paranuclei at the posterior head, and microtubular axoneme of the tail represented 9+9+2 type. The annual reproductive cycles could be divided into five successive stages : growth(March to July), maturation(May to September), Spawning(mid May to early October) and resting stages(October to February). The spawning peak occurred from June to August.
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1. Territorial male threespine sticklebacks, Gasterosteus aculeatus, do not always attack an intruder (a dummy) with red undersides more than one lacking this feature even when it is presented within their own territory. Males in this study showed an overall tendency to bite a dummy without red undersides more than one with this feature during both simultaneous and serial presentations. 2. Considerable variation in attack rates exists between individual males, but whether or not a given male attacks the nonred dummy more appears to be unrelated to whether he exhibits high or low attack rates. 3. Males showed an increased attack rate after they acquired eggs in their nest, but the tendency for a male to attack the nonred dummy more than the red one appears to be unchanged after he acquires eggs. 4. It is suggested that the nuptial coloration of male threespine sticklebacks be interpreted more generally as an indicator of the male's social and physiological status, emphasizing its intimidating effects as well as its aggression eliciting effects for rival males. This is consistent with the observation that nuptial coloration is capable of increasing avoidance as well as attack in rival males and increasing sexual attractiveness to females.
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Changes in gonadosomatic index (GSI), hepatosomatic index (HSI), gonad stage and plasma concentrations of sex steroids were studied over one year in black bream (Acanthopagrus butcheri). Black bream have an annual reproductive cycle with a 3-month spawning season in spring–early summer. GSI and HSI values were highest in October and May respectively. Plasma concentrations of oestradiol-17β (E2), testosterone (T) and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) were highest in females in October. Plasma concentrations of E2 and T were highest in ovulated fish. Concentrations of 17,20βP were higher in fish undergoing final oocyte maturation (FOM) than in fish with regressed gonads. In males, plasma concentrations of T and 11-ketotestosterone (11KT) increased in September and remained elevated until January, but concentrations of 17,20βP did not change with season. However, 17,20βP concentrations in spermiated fish were higher than in non-spermiated fish. Daily changes in gonad condition indicated that females undergo daily cycles of ovarian maturation with ovulation occurring after midday. Plasma T and 17,20βP concentrations of females were elevated at midday in association with FOM, but E2 showed no diel change. In males, partially spermiated fish were dominant in the early morning and fully spermiated fish at midday. Plasma T, 11KT and 17,20βP concentrations were low at midnight and reached maximum levels at 0600 hours.
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Observers onboard commercial trap vessels quantified the sizes of fish in the discarded and retained catch for the major species in the New South Wales (NSW) demersal trap fishery. Selectivity ogives were calculated for the two mesh types used in the fishery, 50mm hexagonal wire mesh and 50mm×75mm welded mesh, by comparing the sizes of fish retained in traps with these meshes with the sizes of fish retained in control traps of 37mm hexagonal wire mesh. The selectivity of 50mm hexagonal wire was inappropriate for all important species with minimum legal size limits in the fishery, with large proportions of catches being undersized fish which were subsequently discarded with unknown mortality. Traps with back panels of 50mm×75mm welded mesh significantly reduced the catch of undersized fish, but also reduced the catches of important species without minimum legal size limits. Mesh selectivity was a direct function of fish body depth and the maximum aperture of the trap mesh on the back panel of fish traps.
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The seasonal circulation associated with the East Australian Current is examined using a set of steric heights derived from the historical hydrology and expendable bathythermograph data collected in the region. The data are separated into a network of regional bins allowing for known oceanographic and topographic features and a two-harmonic best fit to the seasonal cycle is obtained in each bin. Maps of the annual- frequency component of the surface and depth-integrated steric heights ( h and P) show the development and progression of the EAC flow regime through a complete seasonal cycle. The EAC has a strong seasonal cycle from 25øS to 45øS, with strongest southward flow in austral summer. The seasonal cycle in surface flow over the continental shelf is documented by two independent methods, geostrophically, using cross shelf sea level gradients derived from coastal tide gauge data and steric heights at the continental shelf edge, and directly from merchant ship observations. The two estimates are in good agreement. The seasonal cycle in the EAC is more pronounced than in other midlatitude western boundary currents for which data are available. At 28øS, the strength of the total Tasman Sea transport (southward flow) varies between a minimum transport of 7 Sv in winter (July) to a maximum of 16 Sv in summer. The semiannual frequency components of h and P is important near 30øS near the EAC outflow, but not elsewhere. The seasonal cycle of the EAC is not due to strong seasonal variations in Tasman Sea wind stress curl east of the region of interest. Seasonally reversing zonal flows occur offshore north of 25øS, which are apparently locally forced by reversing wind stress curls; but if these flows were fed from the south by the EAC current system, the EAC would have to be weaker in summer, not stronger. The Leeuwin Current Extension along Australia's west and south coasts may pass up the east coast of Australia, providing an important contribution to the enhanced southward flow of the EAC in summer. The vigorous anticyclonic eddies of the EAC also show a marked seasonal cycle, and this is probably an important part of the mechanism for the strong seasonal cycle of the EAC south of 25øS. The location of the strongest anticyclonic eddy in the EAC moves steadily southward throughout the summer season, and the phase of the coastal EAC appears also to move southward, contrary to the expectations of linear theory and to the hypothesis that the Leeuwin Current Extension is the major cause of the seasonal cycle.
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In the tropics, the longnose filefish Oxymonacanthus longirostris spawns shortly before sunset. In subtropical Okinawa Island, Japan, however, diel spawning time changed seasonally depending on seasonal changes in water temperature. At that site, spawning occurred in the morning during the early and late breeding seasons, when water temperatures were low. In the middle breed- ing season, when water temperatures were high, spawning occurred shortly before sunset. Hatching time of embryos was fixed, however, as embryos hatched just after sunset on the second day after spawning throughout the breedmg season. Thus, the incubation period from fertdization of eggs to hatching of embryos changed seasonally and was negatively correlated with water temperature. The cumulative temperature from fertilization to hatching was almost constant throughout the breeding season, contributing to the control of larval development rather than the timing of hatching. Conse- quently, the developmental stage of newly hatched larvae was similar throughout the breedng season. In a rearing experiment that manipulated water temperatures, larvae which hatched at lower than nat- ural ranges of cumulative temperatures were at an extremely immature developmental stage com- pared to larvae in natural temperature conditions. When water temperatures are low in the breeding season, 0. longirostris parents shift their spawning time to the morning to ensure their embryos hatch as well-developed larvae. In conclusion, seasonal variation in the diel spawning time of subtropical 0. longirostris assemblages will be a local adaptation to the strong seasonal changes of water temperature in their environment.
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Paternal care is predominant among telcost fishes with external fertilization. This study describes maternal care in a haremic coral-reef fish and discusses the possible factors leading to its evolution. Both sexes of the triggerfish Rhinecanthus aculeatus (Balistidae) maintained territories; some individuals for more than 8 years. Each male's territory overlapped 2-3 female territories. Pair-spawning occurred around sunrise. Only females cared for the demersal eggs until hatching, which occurred just after sunset on the day of the spawning. No predation was observed on eggs under the maternal care, but experimental removal of parental females decreased the hatching rate to nearly zero. Egg-guarding females foraged as frequently as males, but less than half of non-spawning days. Spawning occurred only in the periods of about 1 wk around the new or full moon, and individual females spawned up to three times in each period. Thus, the maternal care did not significantly affect the duration of the females' spawning intervals, while males would suffer mate loss if they performed parental care. In this situation, maternal care should be the evolutionarily stable strategy. Evolutionary transition from no care to maternal care and then to biparental care is suggested in the Balistidae.
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Groups of the triggerfish Pseudobalistes fuscus and Odonus niger were studied from the underwater laboratory Neritica in Eilat, Gulf of Akaba, in the Red Sea. Mating and the roles of the sexes during broodcare seem to depend strongly on territory size, probably determined by shelter site and food availability, and territorial control- and defendability. The discussion considers why evolution has favoured maternal broodcare in the one case and biparental in the other.
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During the Austral summer of 2006-07 a series of extreme oceanic events occurred in the Tasman Sea. Following a series of strong wind-driven upwelling events, an intense cold-core eddy developed off Sydney, Australia. A data-assimilating, eddy-resolving ocean model is used to create a three-dimensional time-varying reanalysis of these events. The reanalysis indicates that the cold anomalies associated with the upwellings were in excess of -5 o near the coast, where sea-level decreased by as much as 0.2 m. The reanalysed three-dimensional structure of the cold-core eddy shows the eddy "leaning" to the west-north-west, in towards the continental shelf. The diameter of the eddy is about 100 km and the sea-level anomaly at the eddy centre peaks at around -1 m, with an associated sub-surface temperature anomaly in excess of -8 o C at 200 m depth, corresponding to an upward isotherm excursion of 600 m. The circulation around the cyclonic eddy is ageostrophic, with upwelling in the southern sector of the eddy (where flow is onshore and climbing the continental slope) and downwelling in the southern sector (where flow is descending off the slope). Three-dimensional trajectories of water parcels around the eddy involve 50-100 m vertical excursions. Based on the reanalysed circulation and composite satellite images of Chlorophyll-a, we hypothesise that the circulation around the eddy led to significant nutrient enrichment in the euphotic zone around the perimeter of the eddy.
Article
The Pacific coastal areas of Japanese Island are major spawning grounds of various fishes. It is considered that large amount of eggs and larvae are dragged into the Kuroshio front so that the survival of fish larvae at the front is important for their recruitment. From this viewpoint, a low-salinity water mass, which was withdrawn from the coastal area to the Kuroshio front, was investigated by drifters, in addition to fine-scale hydrographic observations and water sampling in and around the Kuroshio frontal area off Enshu-nada. The drifters were transported to the east within the low-salinity water along the Kuroshio front in the first stage, and were thereafter entrained into an eddy, which was caused by the frontal meander. They moved closely to each other along the front, but diverged in the eddy. This movement of the drifters coincided with the deformation of low-salinity water mass; the low-salinity water concentrated at the Kuroshio front surrounded by strong salinity gradients at first, while it spread out horizontally and became vague in the shallow surface layer in the frontal eddy. Comparing temperature sections across the front, the strong upwelling was detected in the eddy. Limiting factors for primary production and growth rates were calculated in six sections using the observed temperatures and concentrations of nutrients. In the frontal area of the Kuroshio, low concentration of nutrients limited the primary production shallower than 50 m. Due to the low productivity, concentration of chlorophyll a in the low-salinity water tended to decrease, although the initial concentration was high. Once the coastal water mass was entrained into the frontal eddy, on the contrary, the concentration recovered due to the enhanced primary production in the subsurface layer supported by the upwelling of nutrient-rich water. Fish larvae in the low-salinity water are assumed to use the new production in the eddy; otherwise, they would starve. The entrainment process, which was probably caused by offshoreward movement of the Kuroshio, holds the key to successive survival and recruitment of fish larvae in the Kuroshio system. D 2002 Elsevier Science B.V. All rights reserved.
Article
Reproduction and parental care in the cockscomb prickleback, a Pacific coast intertidal fish, were examined using a combination of field and laboratory observations. The sexes were dimorphic, particularly during the breeding season, and males competed with other males for access to females. Males performed lateral and spasm displays. In the wild, the breeding season extended from January to March on cobblestone beaches. Assortative mating was positive with respect to body size. Females exhibited solitary parental care of the eggs. Each female coiled around, guarded and fanned a single egg mass that likely represented her total reproductive effort for the year. The number of eggs in the mass increased linearly with female size (weight or length). Males did not remain after spawning. Aquarium observations revealed that males spawn with more than one female given the opportunity. It is not known whether this occurs in the wild. Incubation to hatching took 29 days. Upon hatching, the young swam towards the surface. Parental care did not extend beyond hatching.
Article
The reproductive biology of 315 cobia, Rachycentron canadum, from northeastern Australia was studied for an 18-month period. Cobia ranged from 181 to 1,470 mm FL (0.06–55 kg). Length–frequency distributions of males and females did not differ significantly. The sex ratio of females to males was 2.18:1. Histological data showed that cobia developed hydrated oocytes during a protracted spawning season between September and June. Gonadosomatic index peaked from October to December, coinciding with the monsoon or “wet” season. Estimated length at first maturity for female cobia was 671 mm FL. Length at 50% maturity (L 50) for females was estimated at 784 mm FL (1–2 years of age). Batch fecundity ranged from 577,468 to 7,372,283 eggs with a mean of 2,877,669 (± SD 1,603,760) eggs. Relative batch fecundity was 249 eggs per g, and no relationship between relative fecundity and fork length was found. There was a significant positive relationship between the total number of eggs produced and fork length. Spawning frequency, estimated by the post-ovulatory follicle method, was 7.6 days. Based on the detection of hydrated oocytes in fish caught at night, cobia most likely spawn at night. Cobia also feed throughout the spawning period. This is the first report on the reproductive biology of cobia in Australian waters, and provides valuable data for future population assessments of cobia throughout the Indo-Pacific.
Article
The longnose filefish (Monacanthidae, Oxymonacanthus longirostris) was studied at a patch reef on Enewetak Atoll. It swims with undulations of its median fins and feeds almost continuously on coral polyps, using its beak-like mouth. The spot in the tail resembles an eye so that the tail looks like a head when it protrudes from the coral during feeding. There is slight dichromatism in that males have brighter pelvic flaps. Most of the fish were color tagged for individual recognition. They tended to remain within a given area, although some fish roamed throughout the patch. Most of the larger adults formed monogamous pairs; the smaller fish were variously alone or in groups of 1–5 individuals who appeared to know one another. Only pairs having the largest males, on the periphery of the patch, were clearly territorial. Aggression was a common event featuring a few distinctive displays, most of which were used in courtship as well. Spawning may be a daily event, occurring around 1600 h. The female probes and selects a tuft of blue-green algae; the male nuzzles the female and they spawn in the algae. The green eggs are about 0.7 mm in diameter, demersal, adhesive, and hidden in the algae; they hatched in 53.5 h, just after sunset. The planktonic larvae fit the monacanthid type B of Leis & Rennis (1983) and were initially 2.5 mm TL; by day 5 their yolk was gone.
Article
The endemic filefish, Pervagor spilosoma, has long been known to recruit infrequently but in large numbers to shallow water habitats in Hawaii. When it does recruit, as it did in 1944, 1975 and 1982–1987, it becomes the most abundant or one of the most abundant species on Hawaiian reefs. At these times of high abundance, juvenile individuals also become abundant in the off-shore pelagic environment and in deeper benthic habitats. The results of two previously published studies and this one show that the last heavy recruitment occurred throughout the Hawaiian Island chain in the period from 1982–1988. The earliest strong recruitment in this interval occurred on the leeward, or northwest Hawaiian Islands in 1982, then on Oahu in 1983, then on the island of Hawaii, at the southeast end of the island chain in 1985. At the Kaneohe Bay, Oahu, sampling site, strong recruitment occurred in 1983–1987. Fish that had recruited in the summer of a year survived less than a year at these shallow (<15 m) sites or moved off the reefs. No other fish species among the 30 species censused in a 20 year period at Kaneohe Bay has shown the extremes of abundance displayed by this species, nor did any other species recruit so strongly in the 1983–1987 period. The latter event suggests that the pattern of recruitment in this species was not solely due to a particular pattern of ocean circulation, because if that were the case, other species would also show strong recruitment. The rarity of large recruitment events in this species, the high density of the recruits, the length of individuals at recruitment, the observation by others of juveniles and possibly young adults in the water column, and the sequential nature of the recruitment down the length of the island chain may in part be the result of metamorphosis in the pelagic environment and a pelagic juvenile stage in this species.
Article
The Japanese filefish Paramonacanthus japonicus has extreme sexual dimorphism in its overall shape, even though its mating system is monogamy with biparental care. This sexual dimorphism is mainly due to the development of secondary sexual traits in males. Males become more slender in body with elevated soft dorsal and anal fins as they mature. We examined the function of such male secondary sexual traits by field research and fluid-dynamic analysis. Underwater observations showed that movement rate and steady swimming speed of males were higher than those of females. Male and female P. japonicus showed similar feeding habits and egg-tending behavior, although males attacked potential egg predators more frequently. A wind-tunnel experiment using the air bearing and spring system showed that the drag coefficient of males was significantly lower than that of females, indicating a lower male hydrodynamic drag performance. Also, male elevated soft dorsal and anal fins are considered to give rise to higher thrust performance in monacanthids. Thus, these results suggest that male secondary sexual traits are hydrodynamic devices for enhancing swimming performance that seem to be actually functional under natural conditions. We discuss the evolution of such conspicuous male sexual traits in P. japonicus.
Article
Reproductive habits of a temperate filefish, Paramonacanthus japonicus, were studied on a rocky reef at Tsuyazaki, Fukuoka, Japan, from 1989 through 1990. Males had territories of 30–70m2 and defended them from conspecific males and potential egg predators such as another filefish, Stephanolepis cirrhifer. Egg masses were found on the sandy bottom in male territories. Individual discrimination of males and females occurring in three male territories revealed that males and females stayed in stable pairs during one month of observation in 1989. In these stable pairs, males fed only within their territories, but females occasionally foraged outside. The occurrence of egg masses within male territories and biparental egg care showed that fish were reproducing as monogamous pairs. Contrary to this, males tagged in 1990 changed their territories after the disappearance of females, and males and females mated polygamously. Spawning was observed only four times during the study period, between 1633 and 1754h. Prior to spawning, the female prepared a spawning bed on the sandy bottom. The male nuzzled the female and the pair spawned, touching their gonopores on the spawning bed. Spawning was very quick and took only 1–3 seconds. The adhesive eggs were spherical with a diameter of 0.56 mm. They were mixed with sand particles and formed a doughnut-shaped mass of about 4 cm in diameter. One egg mass contained 3300–3800 embryos of similar developmental stage, which hatched 2–3 days later. P. japonicus appears to be monogamous but may also practice polygamy when pair-bonds are unstable.
Article
The reproductive behaviour ofRudarius ercodes is described from undersea observations in Aburatsubo Bay, Japan. Reproductive behaviour can be separated into four parts: (1) Prespawning Search = searching for spawning sites by females and searching for gravid females by males, (2) Spawning Parade = males follow a gravid female in a line, competing with each other to reach the head of the queue, (3) Spawning = the female takes the spawning position, males rush to the side of the female, and mating occurs between one female and several anterior males of the spawning parade, (4) Parental Care = females attach adhesive eggs to seaweed with the mouth and guard them until embryos hatch. There is no male parental care. The reproductive season ranges from May to October and spawning occurs early in the morning every day. Females begin feeding early in the morning, but males feed little at this time.R. ercodes shows neither territorial behaviour nor fixed-pair spawning. One male might spawn several times in one morning. One female spawns at most once every 5 days. The mating system of this species is promiscuous. The probable function of the spawning parade as a style allowing female choice is discussed.
Article
The triggerfishPseudobalistes flavimarginatus has a lek-like spawning system at Yonge Reef, Great Barrier Reef. Males migrate to a traditional mating ground where they establish territories enclosing nest sites and egg chambers. Females arrive several days later and choose a male for mating. There is biparental care of the fertilized eggs and a strict division of labour. Females appeared to be confined to the nest site by the male. Mating was semi-lunar: eggs were observed in nests several days before the new and full moons on days when high tide occurred near sunset. Differences were observed in the spawning system of another triggerfish (P. fuscus) between the Great Barrier Reef and the Red Sea. Observations of another triggerfish (Balistoides viridescens) are also reported.
Article
Reproductive behavior of the Japanese filefish, Rudarius ercodes, was studied at the rocky reef off Koinoura, northern Kyushu, Japan, between June and October 1989. Aggressive display was observed between males, but they were not territorial. Males had four types of courtship behavior: vibrating, tail bending, leaning and nuzzle. Spawning occurred early in the morning. A female and 1–3 male(s) mated together on brown algae. Each female spawned repeatedly with an interval of 6–12 days. Females cared for eggs and embryos from just after spawning until hatching, 2–4 days. Female egg care consisted of tending and guarding. Females tended eggs by blowing water on them and by fanning them with their pectoral fins. Females guarded eggs by driving away fish passing nearby. In some cases, males also guarded eggs by staying near the eggs and driving away conspecific males. Whether a male cares for eggs with a female seems to be affected by the form of mating (pair mating or single female-multiple male mating), and the probability of further reproduction after spawning. Dominant males showed a tendency to pair with a specific female intermittently over a two-month period. Mating, however, did not always occur between members of such pairs, and mates appeared to be inter-changeable with a promiscuous mating system.
Article
The endemic filefish Pervagor spilosoma appeared in exceptionally large numbers throughout the major Hawaiian Islands during the spring of 1985 and remained abundant through 1988. We examined this occurrence with a perspective gained from studies of reef communities at the Island of Hawaii by one or both of us during most years from 1969 to 1994. P. spilosoma is known to vary in numbers, but such great abundances are rare. Although the species is considered a reef fish, individuals constituting the abundance were mostly in the water column, and spread from coastal reefs to the pelagic zone offshore. One might assume they represented an extraordinary recruitment of pelagic juveniles in the process of shifting to benthic habits, but our data indicate a more complex situation. Individuals in the water column tended to be larger than individuals near the reef, and although the former were feeding on plankton when collected, many had shifted to planktivory from earlier feeding on the benthos. Also, many in the water column were ailing, with moribund and dead individuals common, and these tended to carry parasites of types known to induce their hosts to rise toward the surface. We suggest that the great number of filefish we observed above near-shore reefs represented the shoreward fringe of a vast pool of individuals, varied in age, that had accumulated during the exceptionally long pelagic-juvenile period that is characteristic of tetraodontiforms.
Article
We examined early life history traits and patterns of settlement of the slender filefish, Monacanthus tuckeri, at Calabash Caye, Turneffe Atoll, Belize. A settlement peak was evident at the new moon, and no settlement occurred at the full moon. However, settlement rates at the quarter moons could not be estimated due to sampling gaps. Many reef fishes show new moon settlement peaks, so M. tuckeri shares some characteristics with the primarily perciform species on coral reefs. Pelagic larval duration was long (mean = 42days) and variable, suggesting that dispersal patterns might be diverse. Size at settlement was large (mean = 32mm total length) and also variable. Larval duration and size at settlement were outside of the average values exhibited by reef fishes, but are not beyond the extreme end of the range, and might be explained by association with pelagic debris prior to settlement. There were no differences in overall settlement rates on reef and seagrass habitats, and fish settling to either habitat did not differ in larval duration, size at settlement, or larval growth rate. This suggests that settlement to alternative habitats may be random, or driven by availability of suitable microhabitat, rather than habitat quality or individual traits.
Article
The longnose filefish,Oxymonacanthus longirostris, usually lives in heterosexual pairs, the male and female swimming together and sharing the same territory. Pair territoriality in the species was examined in detail in relation to sexual differences in territorial defense activities. Rigorous pair territoriality was maintained only during the breeding season, although pairs used their home ranges exclusively to a certain extent, during the non-breeding season. The frequency of aggression against other conspecific pairs in the breeding season was higher than in the non-breeding season. Agonistic interactions appear to be over both mates and food resources, the strict pair territoriality in the breeding season possibly being due to mutual mate guarding. In intraspecific aggressive interactions, males usually led their partner females when attacking intruders. The feeding frequency of males was much lower than that of females in the breeding season. Mate removal experiments indicated that females could not defend their original territories solitarily and their feeding frequency decreased. Conversely, males could defend territories solitarily without a decrease in feeding frequency. These results suggest that males contribute most to the defense of the pair territory, with females benefiting from territorial pair-swimming with their partner males.
Article
The mating system of the longnose filefish,Oxymonacanthus longirostris, was examined on coral reefs of Okinawa, Japan. This species has been shown previously to be monogamous. Fish were usually found swimming together in heterosexual pairs with the male and female sharing the same feeding territory. However, both monogamous and polygynous (bigamous) males were found in the present study. Polygynous males, which were larger than monogamous males, visited and stayed several minutes in turn with each female within the territories. Although most males were monogamous in the early breeding season, over 20% of males mated polygynously in the late breeding season. The adult sex ratio in the former was unbiased, but became slightly female-biased toward the end of the breeding season because of the higher disappearance rate of males. The higher disappearance rate may be due mainly to a higher mortality rate of males resulting from a greater deterioration of physical condition during the breeding season. Thus, the mating system varied with the change of the adult sex ratio. Plasticity in the mating system of this species may be the outcome of male mating tactic depending on local mate availability.
Article
Reproductive ecology of the crosshatch triggerfish, Xanthichthys mento (Balistidae) was studied at Hachijojima, Izu Islands, Japan. Males established territories and repeatedly chased females passing nearby. There were 1–3 females in each male's territory before spawning and during egg care. This species spawned in pairs on the sandy bottom. Eggs were scattered and attached to sand particles. Females care for the eggs by blowing water on them and guarding them against intruders, while males helped in guarding. Thus, biparental egg care was observed for 2 days until hatching. Both the males and females disappeared from the territories after the egg care. The reproductive ecology of this species is compared with that of other balistids and the unique features of X. mento are described.
Article
Fishes associated with drifting seaweed were sampled in the Tohoku area, northwest Pacific, in late spring 1988, to analyse the community structure and ecological relationships of the dominant species.Seriola quinqueradiata Temminck et Schlegel was the dominant species and its escort was composed ofThamnaconus (Navodon)modestus, Sebastes inermis, Hyperoglyphe japonica andEnedrias nebulosus. E. nebulosus, which fed essentially on Gammarid crustaceans, was collected mainly in Sendai Bay; the other species, found in offshore water, were plankton feeders and did not exhibit any strong competition, indicating close cohabitation. The abundance of drifting seaweed in the Tohoku area peaked in May–June and decreased in July; they seemed to come from the nearest coast. JuvenileS. quinqueradiata (> 15 cm long) were collected with set nets in Sendai Bay during summer. They seemed to use drifting seaweed (along with the warm Kuroshio current) as a means of transportation during their migration from the southern spawning ground to northern Tohoku area. Drifting seaweed could be considered as a nursery, and the association of fishes with floating algae might have an influence on species recruitment.