ArticlePDF Available

Abstract and Figures

A preview of the PDF is not available
... Both are omnivorous and can thrive on a wide range of food types and food sizes. C. aenus is a bottom feeder and phytophilic spawner with near-internal fertilization (Kohda et al., 1995;Huysentruyt and Adriaens, 2005). Because of its tolerances and traits, it is widely distributed throughout South America east of the Andes (Burgess, 1989) and is a commonly used aquarium species (Huysentruyt and Adriaens, 2005;Axelrod, 2006). ...
... C. aenus is a bottom feeder and phytophilic spawner with near-internal fertilization (Kohda et al., 1995;Huysentruyt and Adriaens, 2005). Because of its tolerances and traits, it is widely distributed throughout South America east of the Andes (Burgess, 1989) and is a commonly used aquarium species (Huysentruyt and Adriaens, 2005;Axelrod, 2006). A. lacustris is one of the most widely distributed South Amercan fish species, with multiple local morphological adaptations that were recently synonymized into a single species (Lucena and Soares, 2016). ...
Article
Full-text available
Biomonitoring is critical for characterizing and monitoring status, spatial patterns, and long-term trends in the ecological condition of freshwater ecosystems. The selection of cost-effective bioindicators is a critical step in establishing such monitoring programs. Key indicator considerations are a reliable response to anthropogenic disturbances, a high benefit-cost-ratio and sensitivity at multiple spatial extents. We evaluated non-linear responses of Ephemeroptera, Plecoptera and Trichoptera (EPT) and fish to the effects of native vegetation loss within buffers of 100 m and 1000 m and assessed the sampling and processing costs involved for each assemblage. We sampled 37 neotropical stream sites in the Formoso River network, a karstic region of the Bodoquena Plateau, midwest Brazil, lying in the ecotone between the Cerrado and Atlantic Forest biological hotspots. We used TITAN (threshold indicator taxa analysis) to identify six indicator taxa, four EPT genera and two fish species. The four EPT genera had low negative thresholds to native vegetation loss, whereas the two fish species had positive thresholds. Thresholds were lower for the 100 m buffers than the 1000 m buffers for EPT. The most sensitive taxon (Macronema, Trichoptera) had a threshold of 0% native vegetation loss in the 100 m buffers and nearly 40% in the 1000 m buffers. For taxa richness, we found no non-linear response to the effects of native vegetation loss for buffer extent nor assemblage. The total cost for EPT biomonitoring was US$ 3,616; whereas for fish, the total was US$ 1,901. Although fish were less expensive than EPT, they did not respond negatively to native vegetation loss and their positive threshold started at 48%, a level of vegetation loss that was highly disruptive of EPT. Therefore, we do not recommend using fish to monitor the effects of native vegetation loss on headwater streams in the Bodoquena Plateau. Although EPT monitoring costs 52% more than fish assemblage monitoring, it detected earlier impacts of the effects of native vegetation loss on stream biota, especially in the 100 m buffer. Therefore, EPT are more cost-effective early warning indicators for monitoring the effects of native vegetation loss in Bodoquena Plateau headwaters.
... They are found in South America. Almost all the main and tributary water systems of the Amazon River contain pikes, but the composition of species in the watersheds where various species are distributed is different (Huysentruyt and Adriaens 2005;Liu et al. 2019;Lv et al. 2020;Tencatt et al. 2021;Sun et al. 2022). For instance, most mouse fish gather in the middle and lower reaches, where the water flow is relatively gentle, and a few strong swift warriors live in the upper reaches of the river. ...
Article
Full-text available
The Pygmy corydoras Corydoras pygmaeus Knaack, 1966, is the smallest member of the genus Corydoras, belonging to the family Callichthyidae and order Siluriformes. The complete mitochondrial genome of C. pygmaeus was sequenced and assembled using next-generation sequencing technology, and phylogenetically compared with those of other species of this genus. The mitochondrial genome of C. pygmaeus is a circular DNA molecule with a size of 16,840 bp (GenBank no. ON729306). A phylogenetic tree was constructed based on 13 protein-coding genes of C. pygmaeus and 13 species of the family Callichthyidae, which showed that C. pygmaeus clustered with other species of this genus, but was the first branch to differentiate. These results could provide basic data for phylogenetic analysis and population genetic diversity protection of Corydoras and Callichthyidae fish in the future.
... Professional scientists, however, seemed and seem to take "sperm drinking" for granted in both original articles (e.g. HUYSENTRUYT & ADRIAENS 2005;MAZZOLDI et al. 2007; FRANCE- SCHINI-VICENTINI et al. 2007) as well as in text books of ichthyology and reviews (e.g. HELFMAN et al. 2007;NELSON & DEHN 2011;ARMBRUSTER 2011;MOL 2012;PANDIAN 2012;WOTTON & SMITH 2014). ...
Article
Full-text available
In 1995 KHODA et al. published a study, in which they described a "unique reproductive behaviour and a new mode of egg insemination" (p. 1) of the armoured catfi sh Corydoras aeneus. From their observations and experiments the authors claimed to have demonstrated that the females swallow the sperm of males during spawning ("sperm drinking") and that after the passage through the gut these sperm inseminate and fertilize the eggs in the fi n pocket formed by the female pelvic fi ns. Since then sperm drinking seems to be a commonly accepted fact in the primary and secondary scientifi c literature and was never seriously questioned herein. However, the way ejaculated sperm take to inseminate and fertilize egg was vigourously discussed already at the beginning and middle of the 20 th century in the so-called "gray" literature by German and later North American aquarists on the basis of numerous observations, hypotheses and even experiments. For example, SCHUBERT (1907) suggested the oral uptake of sperm by the female and LIEBIG (1912) considered the possibility of "sperm drinking" and the intestinal passage of sperm, but also other fertilization scenarios were taken into consideration. Especially the aquaristic literature from USA favoured the view that eggs are inseminated and fertilized during egg deposition. Later KNAACK (1955 ff.), who intensively studied the reproductive behaviour of several Corydoras spp., confi rmed not only the earliest, but largely forgotten observations made by CARBONNIER (1881), but also plausibly rejected the intestinal passage of sperm performing similar experiments as KHODA et al. We give a brief overview of the lively debate on this subject in the fi rst half of the last century, acknowledge the experiments performed by KNAACK as well as by KHODA et al., and discuss some problems that arise from these studies. Generally, our essay tells about an interesting episode of aquaristics and illustrates how much useful information and ideas are hidden in the so-called "gray" literature. Zusammenfassung: KHODA et al. veröffentlichten im Jahr 1995 eine Studie, in der sie ein "unique reproductive behaviour and a new mode of egg insemination" (p. 1) bei dem Panzerwels Corydoras aeneus beschreiben. Die Autoren glaubten aufgrund von Beobachtungen und einer Reihe von Experimenten nachgewiesen zu haben, dass die Weibchen während des Laichaktes die Spermien der Männchen verschlucken ("sperm drinking") und die Spermien die Eier in einer Flossentasche, die von den Bauchfl ossen des Weibchens gebildet wird, erst nach einer Passage durch den Darm besamen und befruchten. Dieses "Spermatrinken" wird seitdem bis heute in der wissenschaftlichen Primär-und Sekundärliteratur als Fakt angesehen und ist dort unseres Wissens auch niemals ernsthaft in Frage gestellt worden. Demgegenüber stehen zahlreiche Veröffentlichungen in der sogenannten "grauen" Literatur, vor allem Anfang bis Mitte des 20. Jahrhunderts, in denen aufgrund von Beobachtungen, Hypothesen und sogar Versuchen zunächst deutscher, dann aber 10 auch nordamerikanischer Aquarianer heftig diskutiert wurde, wie die Spermien zu den Eiern gelangen und diese befruchten. So vermutete beispielsweise SCHUBERT (1907) bereits ein Aufsaugen der Spermien durch das Weibchen und LIEBIG (1912) erwog die Möglichkeit des "Spermatrinkens" und der Darmpassage der Spermien, doch wurden darüber hinaus noch andere Befruchtungsszenarien vermutet, unter anderem, vor allem in der insgesamt relativ spärlichen nordamerikanischen aquaristischen Literatur, dass die Eier während der Eiablage befruchtet würden. KNAACK (1955 ff.) hat dann nach intensivem Studium des Ablaichverhaltens mehrerer Corydoras-Arten nicht nur die ersten diesbezüglichen, aber zum Teil in Vergessenheit geratenen Beobachtungen von CARBONNIER (1881) bestätigt, sondern bereits 1955 mit Versuchen, die im Wesentlichen denen von KHODA et al. entsprachen, eine Darmpassage der Spermien plausibel zurückgewiesen. Wir geben einen kurzen Überblick über die lebhaften Diskussionen zu diesem Thema aus der ersten Hälfte des vori-gen Jahrhunderts, würdigen die Experimente von KNAACK und von KHODA et al. und erörtern einige sich daraus ergebende Probleme. Generell behandelt unser Essay eine interessante Episode der Aquaristik und zeigt auf, wie viele Anregungen und Informationen in der so genannten grauen Literatur verborgen sind.
... It also indicates a behavioural strategy in its natural habitat whereby the eggs are confined to a single location until hatched. This observation corroborates with Husysentuyt and Adriaens [15] who mentioned that the eggs of armoured catfish Corydoras aeneus (Gill, 1858; Callichthyidae) were found to be very adhesive and opined that it could be because the species is known to inhabit turbid and turbulent waters. Unlike the eggs of H. menoda, non adhesive eggs were reported for Rita rita [16] and Trichogaster fasciata [17] . ...
Article
Knowledge of the early life stages of fishes portrays the morphological changes they undergo during embryogenesis and early ontogenesis which aids in their culture and preservation. This study investigated the embryonic and larval development of the menoda catfish, Hemibagrus menoda from fertilization to post - hatching. The ovulated eggs were placed in convex slides and the embryonic and larval developmental stages studied under the microscope. Unfertilized eggs were sticky, mean egg diameter increased from 0.8 ± 0.00 mm to 1.10 ± 0.01 mm after fertilization. Cleavage stage occurred within 2. 50 hr and hatching occurred at 19.30 hr after fertilization at 24.1 0 C water temperature. Newly hatched larvae were curved, laterally compressed with the body gradually tapering towards the tail and measured 3.0 ± 0.02 mm. The egg yolk became completely absorbed within 68 hours at mean length of 6.5 ± 0.05 mm. Findings from this study might aid in the development of appropriate culture program for this species hence preventing its extinction.
... Existe uma série de estudos quanto a aspectos reprodutivos de espécies de Corydoras (Loir et al., 1989;Aranha et al., 1993;Bervian & Fontoura, 1994;Kohda et al., 1995;Paxton, 1997;Pruzsinszky & Ladich, 1998;Kaatz & Lobel, 1999;Alkins-Koo, 2000;Huysentruyt & Adriaens (2005); Mazzoldi et al., 2007;Rondineli & Braga, 2009;Mahapatra & Dutta, 2014). No entanto, informações sobre C. aeneus na região estudada ainda são escassas. ...
Article
Full-text available
RESUMO Apesar do crescente número de estudos sobre biologia de espécies de peixes de pequeno porte, o conhecimento dos aspectos básicos da biologia da maioria das espécies ainda é incipiente. Com isso, o objetivo desse estudo foi descrever alguns aspectos populacionais e reprodutivos de Corydoras aeneus (Gill, 1858) em riachos da bacia do rio Ivinhema, Alto rio Paraná. As amostragens foram realizadas entre 2008 e 2011 em 57 riachos distribuídos na bacia. Foram analisados 684 indivíduos, sendo 213 fêmeas e 190 machos, além de 281 exemplares analisados apenas quanto aos dados de comprimento padrão. O comprimento padrão máximo da população analisada foi de 50,19 mm para as fêmeas e de 45,24 mm para machos; Desta forma, as fêmeas foram maiores que os machos. A proporção sexual foi de 52,7% para fêmeas e de 47,1% para os machos, sem variação significativa entre os sexos (Χ2= 1,313; p = 0,252). Quanto à relação peso/comprimento ambos os sexos apresentaram a crescimento isométrico. As maiores frequências de fêmeas maduras foram observadas nos meses de outubro a dezembro, embora tenham sido observadas fêmeas maduras em outros meses do ano. Estimou-se que 50% das fêmeas estão sexualmente maduras com 33,54 mm de comprimento padrão. A fecundidade média foi estimada em 359,47 oócitos, sendo que a população apresenta desova total. O padrão de recrutamento não apresentou um padrão unimodal, embora a maior intensidade tenha sido observada nos meses de outubro a dezembro. O comprimento assintótico foi estimado em 54,59 mm e a taxa de crescimento de 1,1 ano-1. O índice de performance de crescimento foi estimado em 3,51; a longevidade de 2,72 anos e a mortalidade de 1,48 ano-1.
Article
Artificial reefs are frequently employed in fisheries management to improve the local ecological environment and to contribute to the enhancement of fishery resources. The placement of artificial reefs can attract adult fish, but they also serve as a good environment for sticky fish eggs to hatch and grow. Fish-egg dynamics are highly dependent on the surrounding environment, which is greatly influenced by the configuration of reefs. The scientific design of the reef block number is significant from both an ecological view and economic view. This study sets up a numerical model to simulate the flow field and viscous fish eggs in a reef area, based on the mesoscopic lattice Boltzmann framework coupled with Eulerian and Lagrangian perspectives. This model is verified by particle image velocimetry (PIV), which is a measurement technique for visualizing fluids by displaying velocity vectors in a two-dimensional manner, and obtains the spatial distribution characteristics of fish eggs with various configurations of artificial reefs. To achieve the best configuration of fish reefs in the applied waters, the economic cost and ecological function of fish reefs are balanced using objective analysis. This is a reliable and practical way to take into account capital efficiency and the impact of restoration when designing reef zones.
Article
Full-text available
The sex ratio in spawning can affect the efficiency and success of hatchery activities because sex ratio in spawning affects the number of eggs, the degree of fertilization, and the degree of hatching of eggs. Until now, there is limited research conducted in Corydoras paleatus fish spawning thus this study aims to determine differences in the reproductive performance of C. paleatus with different male sex ratios. This study uses three treatments, which are the ratio of fish male and female (1:1), (2:1), and (3:1). Each treatment uses one female fish. The vessel used in fish spawning is an aquarium with a size of 50 × 25 × 30 cm3. Spawning lasts for seven days and eggs are collected every day at 08.00. The number of eggs and larvae produced was not significantly different between treatments. Larvae produced by C. paleatus were 2,154 fish or 538 fish per female per week. The ratio (1:1) was considered an appropriate ratio in spawning C. paleatus fish because it has a high efficiency value.
Article
Full-text available
Comparative analysis of the mitogenomes of two Corydoras (Siluriformes, Loricarioidei) with nine known Corydoras, and a phylogenetic analysis of Loricarioidei. ZooKeys Abstract Corydoras is a speciose catfish genus from South America with widely investigated phylogenetic and evolutionary relationships. The complete mitogenomes of C. aeneus and C. paleatus were sequenced, assembled , and annotated using next-generation sequencing. The genome arrangements, gene contents, genome structures, base compositions, evolutionary features, codon usage, and tRNA structures of the two mi-togenomes were compared and analyzed with nine published mitogenomes of Corydoras. Phylogenetic analysis was performed using concatenated nucleotide sequences with 13 protein-coding genes and two rRNAs with 44 mitogenomes of Siluriformes. These results provide information on the mitogenomes of eleven Corydoras species and evolutionary relationships within the suborder Loricarioidei, which may be applicable for further phylogenetic and taxonomic studies on Siluriformes and Loricarioidei.
Article
The greenfin horse-faced filefish Thamnaconus septentrionalis is a new marine culture species in East Asia in recent years. It has demersal and adhesive eggs. The artificial fertilization technique of T. septentrionalis has not been established, and commercial hatcheries currently rely on the collection of naturally fertilized eggs. It is impracticable to separate dead eggs from the egg mass, and a large number of waste and faecal matter adhere to the surface of fertilized eggs, causing excess bacterial and fungal loading in eggs incubation tanks. This study aimed to develop an effective method to remove the adhesiveness of fertilized eggs of T. septentrionalis. The effectiveness of tannic acid (0.5%, 0.2% and 0.1%), sodium hypochlorite (0.05%, 0.025% and 0.01%) and alcalase enzyme (4%, 2%, 1% and 0.5%) to eliminate the adhesiveness of T. septentrionalis eggs was evaluated. Eggs were exposed to different deadhesion solutions for up to 20 min, and the number of deadhesive eggs was counted. The results showed that only the alcalase enzyme could effectively remove the adhesiveness of eggs, and the deadhesion efficiency was positively associated with enzyme concentration. The deadhesion rate of the 0.5% alcalase enzyme treatment was more than 70%, while that of the 4%, 2% and 1% alcalase enzyme treatments were more than 90%. The hatching rates were not affected by alcalase enzyme treatment. The hatching rates of the 2% and 1% treatments were higher than those of the control groups. Ultrastructural analysis showed that the surface of eggs had a pore-canal structure, and the zona radiata externa was gradually degraded and finally peeled off during the deadhesion process. Similar to freshwater fishes with adhesive eggs, biochemical analysis showed that the adhesiveness of T. septentrionalis eggs was related to the presence of glycoproteins and mucopolysaccharides in the zona radiata externa. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of zona radiata externa proteins showed that the nonwater-activated eggs, water-activated eggs and adhesive fertilized eggs had same protein pattern, and only small peptide fragments were detected in the deadhesive fertilized eggs. This study provides valuble theoretical and technical support for improvement of hatching technology of filefish.
Article
In teleost, the structural characteristics of fertilized egg and egg envelope are very important for classification of genus or species. The structures of fertilized egg and egg envelope from Corydoras adolfoi and Corydoras sterbai, Callichthyidae, Siluriformes in teleost were examined by scanning and transmission electron microscopes to confirm whether these morphological structures have specificities of species and family or not. The fertilized eggs of C. adolfoi and C. sterbai were non‐transparent, spherical, demersal, and strong adhesive. There were no structural differences between two species through the light microscope. The size of the fertilized eggs of C. adolfoi was 1.95 ± 0.03 mm (n = 20), and that of C. sterbai was 1.92 ± 0.03 mm (n = 20). The perivitelline space was almost not developed in both species. In both species, the adhesive protuberances structures were on the outer surface of egg envelope. And fibrous structures were specially located at attachment part of spawning bed. And the egg envelope consisted of two layers, an inner lamellae layer and an outer strong adhesive layer with high electron dense protuberances structures in cross section. Consequentially, the fertilized eggs, outer surface on the egg envelope and cross section of egg envelope have identical structure. So, these structural characteristics of fertilized eggs and egg envelope show genus Corydoras specificity.
Article
Full-text available
Corydoras difluviatilis, new species, is described from the upper rio Paranaand the upper rio Sao Francisco, Brazil. The new taxon differs from its congeners by three exclusive features: the posterior pectoral-spine serrations restricted to its prox- imal half, and the parapophyses of the fourth free vertebra reduced and separated from each other, not fused into a haemal arch. The new species has several ple- siomorphic character states relative to the assemblage composed of Brochis and most Corydoras species, such as absence of contact between the supraoccipital and nuchal plate, reduction of the ossified portion of hypobranchial 2, and well-developed me- sial expansions of the first and second infraorbitals, indicating its basalmost position within the genus. Corydoras difluviatilis, especie nova, edescrita para o alto rio Paranae alto rio Sao Francisco. O novo taxon difere de suas congeneres por tres caracteres exclu- sivos: o serrilhado posterior do espinho peitoral restrito asua metade proximal, e as parapofises da quarta vertebra livre reduzidas e disjuntas, nao fundidas em um arco hemal. A nova especie apresenta varios estados plesiomorficos em relacao ao grupo formado por Brochis e maioria das especies de Corydoras, tais como ausencia de contato entre o supra-occipital e a placa nucal, reducao da porcao ossificada do hipobranquial 2, e expansoes mesiais do primeiro e segundo infraorbitais bem de- senvolvidas, indicando sua posicao basal dentro do genero.
Article
The surface of eggs of native fishes was studied by scanning electron microscopy and histochemistry. Eggs of representatives of the families Cyprinidae, Salmonidae, Esocidae, Gadidae and Percidae were investigated. The structure of the surface varies in the different species. One can find villi of different length, honeycomb-like structures or surfaces without appendages. Most of the eggs have a sticky outer envelope due to mucopolysaccharides.
Article
Oocytes and eggs from teleost fishes are always surrounded by an egg envelope of variable dimensions. This envelope (zona radiata) of the teleosts normally consists of two layers, a zona radiata interna and a zona radiata externa. The chemical composition of the interna is known to be largely proteinaceous. Neutral and acid mucopolysaccharides are the main components of the externa. The zona radiata is multifunctional even though its primary objective is the protection of the developing embryo. The zona radiata interna is largely responsible for this protective function. This layer hardens after the eggs have been laid and it is known to increase its tensile strength up to a thousandfold. The thickness of the egg envelope is directly related to the mechanical demands which have to be met by eggs and embryos in their particular environment. Normally the zona radiata has a thickness of 5 to 15 μm but it may be as thick as 60 μm in species (i.e. salmonids) which deposit their eggs in pebble beds. Eggs which are deposited in the tidal wave zones may reach as much as 100 μm (i.e. hook-nose Agonus cataphractus). Eggs of teleosts which are protected from mechanical forces are normally much thinner. Species which mouthbreed or have living offspring have a very thin zona radiata. In goodeids and poeciliids the zona is only about 0.5 to 2 μm thick. The zona radiata supplies the eggs with oxygen. In some fish species it has bactericidal properties because it produces hydrogen peroxide and in others it is used to attach the eggs to the substrate where they are deposited. For the latter it is equipped with variable mechanisms as it can form special sticky layers, protuberances, attaching-filaments or a muco-follicle epithelium. This enables not only an attachment to the substrate but the eggs can be placed in assemblages of various kinds and may be protected by the fish species which guard their egg deposits. In bodies of water which have little or very much reduced available oxygen the eggs may be attached to the tips of plants and thus help to ensure adequate supplies of oxygen. The micropylar opening in the egg envelope fascilitates the penetration of the spermatozoa into the eggs and guarantees fertilization. There are various mechanisms which exclude the penetration of more than one sperm cell (= polyspermy). A micropylar lid is particularly important in teleosts as the entry of more than one sperm will result in malformed or even dead embryos.
Article
Both the number of oil droplets within the egg and the external morphology of the chorion of Fundulus heteroclitus were found to vary extensively among populations along the US east coast. The number of oil droplets per egg varied clinally from a mean of 12.7 at Mount Desert Island, ME to 172.3 at Jacksonville, FL for individuals maintained in the laboratory under identical conditions. The pattern of variation in the external morphology of the chorion, as established by scanning electron microscopy, was that of a step cline. The chorion of eggs from Mount Desert Island, ME to Newark Bay, NJ was characterized by a surface sculptured with chorionic papillae approximately 0.5 μ in diameter. The chorionic filaments were smooth and conically modified at the base. Over the same area, the filament diameters ranged from 0.8-2.2 μ and the filament density ranged from 0-5 per 10,000 μ 2 of chorion surface area. In striking contrast, the chorion surface of eggs from Sandy Hook, NJ to Jacksonville, FL lacked papillae, but had granular, pebble-surfaced filaments attached directly to the chorion with no conical modifications at the base. Filament diameters ranged from 0.7-0.8 μ and filament densities ranged from 150-220 per 10,000 μ 2 among these southern populations. Samples from a location intermediate between Newark Bay and Sandy Hook, NJ had an intermediate filament density of 82 per 10,000 μ 2. This pattern of geographic variation in oil droplet number and chorion morphology was repeated within Chesapeake Bay and Delaware Bay. Within Chesapeake Bay, oil droplets varied clinally from 31.5 per egg at an upper bay locality to 102.0 per egg at a lower bay locality. Within Delaware Bay, oil droplets varied from 46.9 per egg at an upper bay locality to 102.7 per egg at a lower bay locality. The chorionic filament diameter and density at the most southern Chesapeake Bay locality was 0.6 μ and 200-210 per 10,000 μ 2 while the filament diameter and density from the most northern locality was 1.9-2.4 μ and 0-2 per 10,000 μ 2. Within Delaware Bay, the filament diameter and density ranged from 0.7 μ and 190 per 10,000 μ 2 at the lower bay locality to 1.9 μ and 0-2 per 10,000 μ 2 at the upper bay locality. On the basis of these characters, upper bay eggs were indistinguishable from eggs of coastal populations north of Newark Bay, NJ while lower bay eggs were indistinguishable from eggs of coastal populations south of Sandy Hook, NJ. We suggest that the present distribution of F. heteroclitus populations of different egg types may reflect the consequences of secondary intergradation, with zones of intergradation at northern New Jersey and within Chesapeake and Delaware bays.
Article
The perivitelline space enveloping the eggs of bony fishes prior to hatching is formed as a result of activation and fertilization and involves an egg shrinkage attributable to a fertilization induced cortical discharge of colloidal material as well as an osmotic distension of the egg envelopes. The perivitelline fluid and its containing multilamellar envelopes with their varied specialized patterns and filamentous elaborations provide a number of protective, nutritive, flotative, polyspermy preventive and regulative functions. Fish eggs and embryos, by monitoring the immediate environment, possibly may modify the colloidal composition of the perivitelline fluid and the substructural organization of the egg envelopes in some instances, thus providing an adaptive mechanism for survival in a polluted environment. The review includes a discussion of the problematic issues surrounding membrane origin, structure and nomenclature, suggestions for further research and an extensive bibliography.
Article
Eggs of 23 Characiformes and eight Siluriformes, belonging to nine families with diverse reproductive behaviour, were ultrastructurally analysed. The migratory species exhibited non-adhesive eggs, whereas, most of the sedentary species presented some degree of egg adhesiveness. Among the Characiformes, non-adhesive eggs showed zona radiata with pore-canals or a fibrillar net at the surface; weakly adhesive eggs presented only zona radiata with pore-canals while adhesive eggs exhibited zona radiata with apparatus like globules, filaments, villi or honeycomb-like pores depending on the systematic group. The ' jelly ' coat is strongly related to the Siluriformes eggs apparently without relationship with adhesiveness. A micropylar disc was present in adhesive eggs of a few species of both Characiformes and Siluriformes. Some patterns were characteristic of the animal pole, others of the vegetal pole, and others were common to both poles. The radial ridges converging to the micropyle in Astyanax bimaculatus lacustris appear to be related to fertilization. In general, egg surface structures in the Characiformes varied according to the genus, whereas all Siluriformes showed a similar egg surface pattern, regardless of the group analysed. Multivariate analysis allowed the identification of eight clusters among the Characiformes and three among the Siluriformes showing relationships between reproductive style and egg characteristics. It is suggested that egg surface and adhesiveness may be related to reproductive patterns and to phylogenesis.
Article
The surface of the whitish translucent egg of Romanichthys valsanicola is sculptured in an irregular honeycomb–like pattern. The micropyle consists only of a type I micropylar channel.
Article
To examine the hypothesis that breathing patterns in fish capable of bimodal respiration can be modified by ecological factors that alter the relative costs of air and water breathing, we determined the air-breathing frequency and activity of a group of Corydoras aeneus before and after presentation of small amounts of food. In nature a reduction in air breathing while feeding on small, patchy resources should reduce loss of food to competitors and lower the risk of failing to relocalize the food source. Activity always increased after food presentation, but the change in air breathing depended on dissolved oxygen tension. Air breathing decreased after food presentation at 116 and 72 torr (1 torr = 133.322 Pa), stayed the same at 44 torr, and increased at 24 torr. This suggests that although oxygen demand increases during feeding, air breathing is decreased when the ambient conditions permit a compensatory increase in the uptake of dissolved oxygen.