[show abstract][hide abstract] ABSTRACT: Flatfish reared for stock enhancement often exhibit irregular behavioral patterns compared with wild conspecifics. These “deficits”, mostly attributed to the unnatural characteristics of the hatchery environment, are assumed to translate to increased predation risk. Initially releasing fish in predator-free conditioning cages may help flatfish adjust to the wild environment, establish burial skills, begin pigment change, recover from transport stress, and experience natural (live) food sources before full release into the wild. However, the impact of cage conditioning on the performance and behavior of flatfish has yet to be fully assessed. We conducted video trials with 10-cm, hatchery-reared Japanese flounder, Paralichthys olivaceus, in sand-bottomed aquaria to assess four treatments of flounder: (1) reared fish cage conditioned for 7 d in the shallow coast, (2) reared fish directly from hatchery tanks, (3) wild fish, and (4) reared fish released directly from hatchery tanks into the wild and then recaptured after 6 d at large. Burying ability, predation, and threat response to a model predator were examined. Wild fish buried most, followed by cage conditioned, and released-then-recaptured and non-conditioned (directly from tank) fish. Wild and conditioned fish revealed much lower variation in total movement duration, which corresponded with lower levels and variation in prey vertical movement. Fish of all condition types exhibited a lower number of attacks and off-bottom swimming events, and a lower movement duration when the model predator was in motion versus when it was still. This study is the first to evaluate the behavioral mechanisms of hatchery-reared flatfish that have been cage-conditioned or released-then-recaptured. In addition, we provide evidence that cage conditioning can enhance the performance of released flatfish.
Journal of Sea Research 01/2014; 85:447–455. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: We assessed whether the development of observational learning in jack mackerel Trachurus japonicus juveniles corresponds with that of their schooling behaviour. Schooling behaviour was quantitatively analysed by nearest neighbour distance and separation angle in two size classes of fish, 20-mm and 40-mm in body length. Observer and non-observer fish with matching sizes were conditioned to pellets by temporarily stopping aeration. Observer fish were provided with five observation trials of other individuals feeding near an air stone when aeration was stopped. After the observation trial, fish were conditioned to pellets with the stop of aeration, and then the learning process was evaluated by the increase in the association with the feeding area when aeration was stopped. In 20-mm fish, which were at an immature stage of schooling behaviour, there was no difference in the learning process between observer and non-observer fish. In contrast, 40-mm fish were confirmed to have a well-developed schooling behaviour, and the observer learnt the feeding area more efficiently than the non-observer. This study provides evidence that observational learning develops along with the development of the social interaction.
[show abstract][hide abstract] ABSTRACT: Animals in social environments can enhance their learning efficiency by observing the behaviour of others. Our previous study showed that learning efficiency of schooling fish increased through the observation of the behaviour of trained demonstrator conspecifics. The present study aimed to verify the key factor of observational learning by investigating what information is important for social transmission of feeding information. A striped jack (Pseudocaranx dentex) observer was provided with one of the five observation treatments: (a) pellets observation, where pellets were dropped near the aeration in an adjacent tank; (b) responding conspecific observation, where a trained conspecific demonstrator responded to the aeration without food in the adjacent tank; (c) foraging conspecific observation, where a conspecific demonstrator foraged near the aeration in the adjacent tank; (d) nearby pellets observation, where pellets were dropped in a transparent column near the aeration in the observer tank; and (e) foraging heterospecific observation, where a filefish (Stephanolepis cirrhifer) demonstrator foraged near the aeration in the adjacent tank. The response to the aeration in these observers was compared with that of controls who did not observe any behaviour. Only individuals who observed foraging conspecifics showed a response to the aeration after observing. These results suggest that observer fish acquire feeding information not through recognition of prey items or through imitation of the demonstrator, but through the vicarious reinforcement of a conspecific for foraging.
[show abstract][hide abstract] ABSTRACT: The amount of ultraviolet (UV)-B radiation reaching the sea surface has increased due to ozone depletion. Several laboratory studies have highlighted the negative impacts of UV radiation on fish using hatchery-reared specimens. However, potential differences in UV tolerance between wild and hatchery-reared fish have been given little consideration. Wild and reared juveniles of red sea bream and black sea bream were exposed to one of four different UV-B radiation levels (1.8; 1.1; 0.4; 0 W/m 2 ) for 4 h. Survival rate was measured every 2 h for a period of 24 h (red sea bream) or 48 h (black sea bream) following exposure. Wild and reared juvenile red sea bream were characterized by similar survival rate, with survival declining to almost 0 % 24 h after exposure at the 1.1 and 1.8 W/m 2 levels. In black sea bream, wild individuals showed significantly higher survival than reared fish in levels 1.1 and 1.8 W/m 2 . Melanophore density was also measured since melanin absorbs UV radiation. Wild black sea bream showed higher melanophore density compared to reared individuals, while no such difference was observed in red sea bream. We conclude that wild black sea bream juveniles acquire higher UV tolerance partly by increasing melanophore density through exposure to UV radiation. Our results indicate that the predicted impacts of UV radiation on fish populations solely based on experimentation with hatchery-reared specimens may be overestimated for some species.
Environmental Biology of Fishes 01/2013; 96:13-20. · 1.31 Impact Factor
[show abstract][hide abstract] ABSTRACT: Laboratory experiments revealed distinct effects of turbidity on the survival of Japanese anchovy Engraulis japonicus larvae when exposed to either visual (jack mackerel Trachurus japonicus) or tactile (moon jellyfish Aurelia aurita) predators. The experiments were conducted in 30 l tanks with three levels of turbidity obtained by dissolving 0, 50 or 300 mg l(-1) of kaolin. Predators were introduced to experimental tanks followed by larvae of E. japonicus ranging from 5 to 25 mm standard lengths (L(s) ). When exposed to T. japonicus, the mean survival rate of larvae was significantly higher in 300 mg l(-1) treatments compared to the other turbidity levels. When exposed to A. aurita, however, there was no difference in the survival rates among different turbidity treatments. The survival rates when exposed to either predator improved with larval growth. The logistic survivorship models for E. japonicus larvae when exposed to A. aurita had an inflection point at c. 12 mm L(s) , suggesting that their size refuge from A. aurita is close to this value. Comparison to a previous study suggests a high vulnerability of shirasu (long and transparent) fish larvae to jellyfish predation under turbidity. This study indicates that anthropogenic increases of turbidity in coastal waters may increase the relative effect of jellyfish predation on fish larvae.
Journal of Fish Biology 12/2011; 79(7):2007-18. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: The ontogeny of swimming speed, schooling behaviour and jellyfish avoidance was studied in hatchery-reared Japanese anchovy Engraulis japonicus to compare its life-history strategy with two other common pelagic fishes, jack mackerel Trachurus japonicus and chub mackerel Scomber japonicus. Cruise swimming speed of E. japonicus increased allometrically from 1·4 to 3·9 standard length (L(S) ) per s (L(S) s(-1) ) from early larval to metamorphosing stage. Burst swimming speed also increased from 6·1 to 28 L(S) s(-1) in these stages. Cruise speed was inferior to that of S. japonicus, as was burst speed to that of T. japonicus. Engraulis japonicus larvae were highly vulnerable to predation by moon jellyfish Aurelia aurita and were readily eaten until they reached 23 mm L(S) , but not at 26 mm L(S) . Schooling behaviour (indicated by parallel swimming) started at c. 17 mm L(S) . Average distance to the nearest neighbour was shorter than values reported in other pelagic fishes. The relatively low predator avoidance capability of E. japonicus may be compensated for by their transparent and thus less conspicuous body, in addition to their early maturation and high fecundity.
Journal of Fish Biology 05/2011; 78(5):1323-35. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: We conducted feeding experiments on threadsail filefish Stephanolepis cirrhifer juveniles for 16days to evaluate the efficacy of moon jellyfish Aurelia aurita as a prey item. Four treatments, each with 40 individuals, were prepared to compare fish growth performance. The treatments
consisted of filefish that were starved (control) (S), fed only jellyfish (J), fed only krill (K), and fed both jellyfish
and krill (JK). Fish in the S treatment exhibited a 50% mortality rate and reduced body weight, whereas the J treatment exhibited
a zero mortality rate and increased body weight. Fish in the JK treatments showed a significantly faster growth than those
in the K treatment. Filefish consumed as much as 24 and 13 times their own body weight in jellyfish per day in the J and JK
treatments, respectively. This is the first report showing that growth can be sustained by feeding a marine fish only jellyfish,
and indicates the potential of jellyfish as a fish prey in both nature and captivity.
[show abstract][hide abstract] ABSTRACT: The swimming angle of larval Japanese anchovy (Engraulis japonicus) was measured in a tank, and target strength (TS) was calculated using a theoretical scattering model. The mean swimming angle was 12.8° (s.d. = ± 22.1). Increased speeds of flow led to increased mean swimming angles. The mean swimming angle at flow of 5 cm s^[-1] was higher than those at other speeds. TS values were estimated using a distorted-wave Born approximation model for two cases. Average values were 1-3 cm s^[-1] (Case 1: 11.5° ± 22.1) and 5 cm s^[-1] (Case 2: 16.6° ± 21.7) for cases 1 and 2, respectively. For case 1, TS ranged from -92.0 to -74.7 dB with a mean of -79.4 dB at 120 kHz. For case 2, TS ranged from -92.2 to -75.2 dB with a mean of -79.9 dB. The mean TS in case 2 was lower than that in case 1, with the maximum difference being 1.0 dB at 120 kHz [standard length 22.0 mm]. However, there were no significant differences between the regression lines of cases 1 and 2. Thus, changes in flow speed altered the swimming angle of larval Japanese anchovy, but had little influence on TS. カタクチイワシシラスのような無鰾魚を対象に音響計測を実施する場合, わずかな姿勢角変化がターゲットストレングスに大きく影響する. 本研究では, 頭部を上向きにした状態で遊泳する傾向が強いこと（平均12.8°, 標準偏差±22.1）, 流速が上昇するとこの傾向が強くなることを明らかにした. また, 分散分析により姿勢角結果を2ケースに分けTSを平均化したが, 両者にほとんど差はみられなかった. したがって, 物理環境により遊泳姿勢にわずかな違いが生じても, 標準偏差が高い場合は平均化TSへの影響は小さいと考えられた.
[show abstract][hide abstract] ABSTRACT: The anti-predatory performance of hatchery-reared red tilefish (Branchiostegus japonicus) using tube-shaped burrows was studied together with the behavioral characteristics of potential predators, the white spotted conger (Conger myriaster) and the marbled rockfish (Sebastiscus marmoratus). White spotted conger were released in Maizuru Bay (Kyoto, Japan) and tracked using acoustic telemetry; they were also observed in a tank using video recording. White spotted conger tended to remain inside shelters, but occasionally swam outside briefly at night. Attacking behavior of predators and predation avoidance behavior of red tilefish were also recorded in a tank. Red tilefish construct tube-shaped burrows into which they retreat to avoid attack. White spotted conger wandered around the tank, often invading the burrows to prey on red tilefish. Predation by white spotted conger occurred at night. Inside the burrows, red tilefish were not easily caught and were able to escape through the other entrance of the tube-shaped burrow. Marbled rockfish, on the other hand, pounced on red tilefish immediately after prey recognition, ambushing their prey near the burrow entrance. Predation by marbled rockfish was frequently observed around dusk and dawn, but some red tilefish that remained inside burrows survived. White spotted conger is nocturnal and probably an olfactory predator, whilst marbled rockfish is crepuscular and an ambush predator. For stock enhancement of red tilefish, the construction of tube-shaped burrows and their diurnal behavior around the burrows are desirable characteristics in reducing predation by both white spotted conger and marbled rockfish.
[show abstract][hide abstract] ABSTRACT: Ontogenetic changes in learning capability were studied in jack mackerel Trachurus japonicus juveniles ranging from 20 to 95 mm standard length (L(S)) collected from either pelagic or coastal habitats. Simple spatial and reversal learning tasks were used to estimate learning capability. There was no size dependence in the scores of simple reward conditioning using a Y-maze, whereas the scores of reversal learning tasks showed a clear sigmoidal curve of increase with an inflexion point at 51·7 mm L(S). The increase in this learning capability coincided with the size at which juveniles recruit from offshore pelagic to coastal rocky habitats.
Journal of Fish Biology 12/2010; 77(10):2315-25. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: Hatching success was examined under exposure to solar ultraviolet radiation (UVR) using filters to give three different light conditions [C1: UV-B, UV-A and photosynthetically active radiation (PAR), C2: UV-A and PAR, C3: PAR] in red Pagrus major and black Acanthopagrus schlegeli sea bream. Hatching rate of both species was reduced by an exposure over a 2 day period to UVR and was not significantly different between two species under the three light conditions.
Journal of Fish Biology 02/2010; 76(3):734-41. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: Flatfishes display a left–right asymmetry that is unique in the animal kingdom. In order to clarify the mechanisms of the
asymmetrical development of pigment cells, changes in pigment cell densities were examined in Japanese flounder Paralichthys olivaceus. During development from symmetrical larvae to asymmetrical juveniles, pigment cell densities were monitored on the skin
on both the left side (ocular side in juvenile; eventually has two eyes) and the right side (blind side in juvenile; eventually
has no eyes). A symmetrical and constant decrease was observed in leucophores and larval type melanophores. A mostly symmetrical
(slightly delayed on the blind side) and constant increase in iridophores from metamorphosis was observed. Adult-type melanophores
appeared and then increased only after metamorphosis on the ocular side. However, the pattern of xanthophores was complicated:
they first existed symmetrically and decreased symmetrically until metamorphosis, and they later increased only on the ocular
side. The dual appearance of the xanthophores, as well as the differences between their depths and sizes on the ocular and
blind sides, may suggest the presence of two types of xanthophores—just as melanophores are well known to exhibit two types.
The ontogenetic study of pigment cells described here is likely to help to elucidate the process of abnormal pigmentation
KeywordsJapanese flounder-Pigment cell-Metamorphosis-Asymmetrical development-Xanthophore-Larval and adult type-Ontogeny-Flatfish
[show abstract][hide abstract] ABSTRACT: Three-day rearing experiments were conducted to study the effect of turbulence on the feeding intensity and survival of pelagic larvae of Japanese flounder Paralichthys olivaceus. Four levels of turbulence as control (10(-7.2) m2 s(-3)), low (10(-6.2) m2 s(-3)), mid (10(-5.6) m2 s(-3)) and high (10(-5.0) m2 s(-3)) were set by changing the flow rate of water pumped through pipes set on the bottom of the tanks. In B-stage larvae, defined as having buds of elongated dorsal fin rays, the feeding intensity and growth were higher in the low and mid turbulence levels, while survival was highest in the control level. Most of the larvae surviving in the control level, however, were judged to be in a seriously starved condition leading to subsequent high mortality. Because the three-day span of the rearing experiments was thought to be a little shorter than the periods before starvation-induced, high mortality occurs. In contrast, for D-stage larvae, their feeding and growth were optimal in the control and low levels. Feeding was more adversely affected in the high level for D-stage larvae compared with B-stage larvae. This is probably due to the compressed body shape and elongated dorsal fin rays of D-stage larvae, which may be more strongly affected by turbulence and, as a consequence, the larval feeding behaviour such as pursuit and capture of prey organisms becomes less efficient than in lower turbulence. Considering the vertical distribution of B and D-stage larvae in the oceanic water column, the optimum turbulence level range found in the present study corresponded to a wind speed of 7-10 m s(-1). Therefore, moderate weather conditions of this wind speed range are considered to potentially enhance survival of early larval stages of P. olivaceus.
Journal of Fish Biology 11/2009; 75(7):1639-47. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: Research related to fish early life history has been one of the major subjects in marine science for various reasons. The practical driving force of studying fish early life history is the concern about the management of fisheries resources (Fuiman and Werner 2002). Although a single parental fish provides a large number of offspring, fish eggs and larvae generally suffer a high mortality rate. As a result, modest differences in daily mortality results in orders of magni-tude difference of recruitment in the long run (Houde 2002). In this monograph, I review research on the ontogeny of anti-predator behavior and con-current developmental changes in pelagic fishes with emphasis on my own work. In Chapter 2, morphological development of a carangid fish, striped jack, Pseudocaranx dentex, was described, Abstract Behavioral ontogeny of marine pelagic fishes is reviewed in the context of sus-tainable fisheries resource management. In carangid fishes, development of sen-sory organs corresponds with their basic behavior such as phototaxis and optoki-netic response, whereas the onset of schooling requires the development of the central nervous systems (CNS). Because docosahexaenoic acid (DHA) is indis-pensable for the development of CNS, quality as well as quantity of prey is impor-tant for the development of behavior and thus survival. Among common pelagic fishes, chub mackerel, Scomber japonicus, had the best growth performance and their cruise swimming speed was remarkably fast. Japanese anchovy, Engraulis japonicus, were slow both at cruise and burst swimming speeds, and were ex-tremely vulnerable to predation by jellyfish. Jack mackerel were slow at cruise swimming speed, but they can make use of jellyfish as a refuge and as a prey collector. Each biotic and abiotic environmental factor, such as water tempera-ture, the amount of phytoplankton, copepods and jellyfish, may work in a positive or negative way for each species, and this can be a driving force for the replace-ment of predominant fish species. Considering that there are always competition and predator–prey relations among different pelagic fish species, ecosystem based management is indispensable for the sustainable utilization of pelagic fishes.
[show abstract][hide abstract] ABSTRACT: Commensal behavior of jack mackerel Trachurus japonicus (Temminck & Schlegel) with jellyfishes has been widely observed but its ecological function is still unclear. The goal of
the present research is to examine the function of association behavior with jellyfish in the laboratory and in field observations
with an emphasis on ontogenetic changes. In the laboratory, jack mackerel juveniles (mean standard length (SL) =11, 19, 38,
and 55 mm) were placed in 500-l polycarbonate tanks with two live moon jellyfish, Aurelia aurita (Linné), and one artificial jellyfish made of silicon. Association behavior with either live or artificial jellyfish was
visually observed under the following conditions: control, presence of a predator model, before and after feeding live Artemia, 1 h and 3 h after feeding, and at night. Jack mackerel at 11 mm SL associated with both the moon jellyfish and artificial
jellyfish, unrelated to the presence of a predator model or feeding. Juveniles at 19 mm associated with moon jellyfish only
in the presence of a predator model. Larger juveniles associated with moon jellyfish at 1 h and 3 h after feeding. Thus the
ecological function of association was proposed to develop first from school formation, next as a hiding place from predators,
and then as a food source. Underwater observations of jack mackerel associating with giant jellyfish Nemopilema nomurai (Kishinouye) in two different areas in the Sea of Japan supported this hypothesis. High predation pressure from benthic piscivorous
fishes in the southern area (Tsushima) may encourage association with jellyfish, whereas pressure from pelagic predators in
the northern area (Maizuru) may encourage settlement to rocky reef habitats in temperate waters. Thus the jellyfish may also
function as a vehicle for the northward migration of this species.
[show abstract][hide abstract] ABSTRACT: Juveniles of carangid fishes including jack mackerel Trachurus japonicus are known to associate with jellyfishes. The function of this association behavior was studied through rearing experiments
and underwater visual observations. Association behavior of jack mackerel with moon jellyfish in experimental tanks was more
frequent in the presence compared to the absence of predators (chub mackerel Scomber japonicus). In the experimental tanks, the presence of jellyfish, however, did not mitigate predation by these predators. Although
jack mackerel did not feed on the jellyfish itself, they frequently fed on the captured prey (Artemia nauplii) whilst in the gut cavity of the jellyfish. Underwater observations of giant jellyfish Nemopilema nomurai off Kyoto and Fukui prefectures revealed that approximately 30% of these jellyfish were accompanied by jack mackerel juveniles
with body sizes ranging 10–45 mm standard length (SL). Considering that jack mackerel juveniles found in subtidal rocky reefs
ranged 40–120 mm SL, we considered that jack mackerel from 10 to 45 mm SL associate with jellyfish as a hiding place as well
as a food collector, until they find a suitable reef habitat when they attain approximately 40 mm SL.
[show abstract][hide abstract] ABSTRACT: Aerial dispersal may be important for redistribution of spider mites into new habitats. Evidence for behavioral control of aerial take-off has been well documented for Tetranychus urticae Koch. Before aerial dispersal they exhibit the aerial take-off posture that involves lifting the forelegs upright and raising the forebody. However, whether the aerial take-off posture functions to increase drag has remained unclear. The objectives of this study were to clarify: (i) aerodynamic effects of the aerial take-off posture; and (ii) actual aerial take-off behavior in T. urticae. To evaluate the aerodynamic forces experienced by grounded spider mites in different postures, we constructed three-dimensional models of T. urticae, exhibiting the aerial take-off posture and the normal posture, using computer graphics. We found that the aerial take-off posture was effective in receiving greater rearward forces from wind rather than upward forces. As a result, aerial take-off from a horizontal platform is unlikely. Instead, inverted departure surfaces, e.g., lower leaf surfaces, with inclines are likely to be effective sites for take-off. Laboratory experiments and field observations indicated that the mites preferentially adopted such a position for orientation and take-off. Our findings provided a rationale for the take-off behavior of Tetranychus spider mites.
Enperimental and Applied Acarology 04/2008; 44(3):165-83. · 1.85 Impact Factor