Development of the neotropical catfish Rhamdia quelen (Siluriformes, Heptapteridae) incubated in different temperature regimes

Different response of females and males Neotropical catfish (Rhamdia quelen) upon short-term temperature increase

Climate change has been one of the most discussed topics in the world. Global warming is characterized by an increase in global temperature, also in aquatic environments. The increased temperature can affect aquatic organisms with lethal and sublethal effects. Thus, it is necessary to understand how different species respond to temperature. This study aimed to evaluate how the Neotropical catfish species Rhamdia quelen responds to temperature increases. The fish were exposed to temperatures of 25 °C (control) and 30 °C after gradual temperature increase for 7 days. After 96 h in each temperature, the fish were anesthetized, blood was collected, and after euthanasia, brain, liver, posterior kidney, gills, muscle, and gonads were collected. The gonads were used for sexing, while other tissues were used for the hematological, biochemical, genotoxic, and histopathological biomarkers analysis. Hepatic proteomic analysis with a focus on energy production was also carried out. Blood parameter changes in both sexes, including an increase in glucose in males, leukopenia in females, and genotoxicity in both sexes. Hepatic proteins related to energy production were altered in both sexes, but mainly in males. Others biomarker alterations, such as histopathological, were not observed in other tissues; however, the antioxidant system was affected differently between sexes. These showed that R. quelen juveniles, at temperatures higher than its optimum temperature such as 30 °C, has several sublethal changes, such as hematological alterations, antioxidant system activation, and energetic metabolism alteration, especially in males. Thus, short-term temperature rise can affect females and males of R. quelen differently.

Sublethal effects of the herbicides atrazine and glyphosate at environmentally relevant concentrations on South American catfish (Rhamdia quelen) embryos

The objective of this work was to evaluate the effects following exposure (96 h) of South American catfish (R. quelen) embryos to active ingredients and commercial formulations from atrazine and glyphosate, isolated and in mixtures, at environmentally relevant concentrations. While the survival rates were not affected, sublethal effects were evidenced after exposure. The most frequent deformities were fin damage and axial and thoracic damage. The mixture of active ingredients caused an increase in SOD and GST, differing from the treatment with the mixture of commercial formulations. The activity of AChE was significantly reduced following the treatment with the active ingredient atrazine and in the mixture of active ingredients. In general, herbicide mixtures were responsible for causing more toxic effects to R. quelen embryos. Therefore, these responses showed to be suitable biomarkers of herbicides' exposure, in addition to generating more environmentally relevant baseline data for re-stablishing safety levels of these substances in aquatic bodies.

From molecular endpoints to modeling longer-term effects in fish embryos exposed to the elutriate from Doce River

Sediments represent a major sink and also a main source of contaminants to aquatic environments. An environmental disaster from a mining dam breakage in 2015 in South-East Brazil re-suspended complex mixtures of chemicals deposited in the sediment, spreading contaminants along the Doce River Basin (DRB) major river course. While high levels of contaminants in sediment were well described, toxicological effects in aquatic organisms were poorly investigated. Thus, the effects of these potentially toxic chemicals were assessed in the present study through different endpoints (biochemical to populational levels) in fish embryos of the South-American silver catfish exposed to elutriates from different sites of the DRB. Despite no significant mortality observed, our results showed that exposure to the elutriates, especially those from the closest site to the dam collapse, caused higher deformities rates and DNA damage in the fish embryos than in the control group. Multivariate analysis showed that these sublethal effects may be related to the high levels of metals introduced by mining activities, compromising long-term survival and reproduction success. In addition, it was possible to observe the influence of other sources of pollutants along the river. According to our data, the mathematical model simulated a significant impact on the population density at longer-term exposure, for the sites that showed the most prominent toxicity responses. The fish embryo toxicity test proved to be an effective assay to assess the ecotoxicological effects of the pollutants from a major river contaminated by a mining dam collapse and showed that the survival rate per se was not a suitable endpoint to assess the toxicity of the pollutants. As a consequence, we contributed to shed a light on a potential underestimated impact of pollutants in sediments of the DRB on the native organisms at distinct biological levels of organizations.

Organic and inorganic pollutants in Jordão and Iguaçu rivers southern Brazil impact early phases of Rhamdia quelen and represent a risk for population

The Iguaçu River basin presents high ecological importance due to its expressive endemic ichthyofauna rate, but chemical pollution may threat this biodiversity. Jordão River is one of the main tributaries of Iguaçu River and contribute to this pollution status, since it drains large agricultural areas receiving domestic and industrial effluents before flowing into the Iguaçu River. The objective of the current study was to evaluate the toxic effects of the Iguaçu, Jordão, and the combination of their waters to the embryo-larval phase of R. quelen, investigating the consequences to the population by means of mathematical modelling. R. quelen fertilized eggs were exposed for 96 h to water samples from Iguaçu River upstream (IR), Jordão River (JR), and downstream of both rivers (MR). The analysis of micropollutants in the water showed that JR presented the most complex mixture of substances and elements, followed by IR, while MR showed the lower number of micropollutants detected. Survival rate was not a sensitive endpoint, while the deformity indices were higher in individuals exposed to water from the three studied sites. Superoxide dismutase activity was increased in MR, while non-protein thiol levels were reduced in MR and JR showing the antioxidant mechanism activation. The mathematical modelling revealed that fish exposed to JR would lead to the greater population reduction (46.19%), followed by IR (40.48%) and MR (33.33%). Although the results showed toxicity in all studied sites, the JR site is the most impacted by micropollutants but decrease its toxicity after dilution with Iguaçu River.

Post hatching stages of tropical catfish Rhamdia quelen (Quoy and Gaimard, 1824) are affected by combined toxic metals exposure with risk to population

Toxic metals and silver nanoparticles (AgNPs) are of great importance as pollutants and their frequent use increases the risk of exposure to biota, but few studies have described co-toxic effects in aquatic organisms. In fish, the method using early stages of development are interesting parameters to validate ecotoxicological studies, and more recently, the use of mathematical models has substantially increased the efficiency of the method. Post hatching stages of native catfish Rhamdia quelen were exposed to single or combined mixtures of toxic metals (Mn, Pb, Hg or AgNPs) in order to study its effects. Fertilized eggs were exposed for 24, 48, 72, and 96 h, where hatching and survival rates, malformation frequency, and neuromast structure damages were evaluated. The results showed alterations in hatching rate after single and combined exposure to metals, but mixtures showed effects more severe comparatively with the single exposures. A similar result including a time-dependent effect was observed in survival rates and incidence of deformities. Overall, embryos and larvae were sensitive to toxic metals exposure while the mathematical modeling suggested a population reduction size including risk of local extinction.

Influence of temperature on larval ontogenesis of Geophagus brasiliensis (Quoy & Gaimard, 1824) (Pisces: Cichlidae)

Studies on the larval development of fish are essential for conservation and improvements in cultivation techniques. Geophagus brasiliensis popularly known as Cará has potential as a fish of interest in ornamental aquaculture. Wild adults of G. brasiliensis were kept in an aquarium for spontaneous reproduction. Newly hatched larvae were transferred to 5-litre aquaria at 22, 26 and 30°C until total yolk sac resorption. Histological slides were used for biometric analysis and monitoring of larval ontogenesis at different temperatures. Histologically, from the first to the fourth days it was possible to identify myomeres, optic vesicle, yolk syncytial layer, brain, heart and differentiation of the eye layers. From the fourth to the seventh days, it was possible to identify mandibular and gill cartilages, swim bladder, liver, prismatic epithelium with striated border in intestine and renal epithelium. All biometric measurements increased over the days, except height and length of the yolk sac, which gradually decreased until the complete resorption of the yolk sac that occurred on the fifth day at a temperature of 30°C, the sixth day at 26°C and the seventh day at 22°C. Morphological events at 30°C such as the reabsorption of the yolk sac, the appearance of cartilage in the branchial arches and differentiation of the layers of the eyes occurred faster compared with the other temperatures tested. Opening of the mouth and digestive tract occurred at a similar time on the fourth day in all temperatures.

Embryonic development of the fire-eye-tetra Moenkhausia oligolepis (Characiformes: Characidae)

This study describes the embryonic development of Moenkhausia oligolepis in laboratory conditions. After fertilization, the embryos were collected every 10 min up to 2 h, then every 20 min up to 4 h, and afterwards every 30 min until hatching. The fertilized eggs of M. oligolepis measured approximately 0.85 ± 0.5 mm and had an adhesive surface. Embryonic development lasted 14 h at 25ºC through the zygote, cleavage, blastula, gastrula, neurula, and segmentation phases. Hatching occurred in embryos around the 30-somites stage. The present results contribute only the second description of embryonic development to a species from the Moenkhausia genus, being also the first for this species. Such data are of paramount importance considering the current conflicting state of this genus phylogenetic classification and may help taxonomic studies. Understanding the biology of a species that is easily managed in laboratory conditions and has an ornamental appeal may assist studies in its reproduction to both supply the aquarium market and help the species conservation in nature. Moreover, these data enable the use of M. oligolepis as a model species in biotechnological applications, such as the germ cell transplantation approach.

Sublethal effects of triclosan and triclocarban at environmental concentrations in silver catfish (Rhamdia quelen) embryos

Although banished in some countries, triclosan (TCS) and triclocarban (TCC) have been detected in surface waters in concentrations ranging from ng L^-1 to μg L^-1 and have shown to affect non-target organisms posing risk to aquatic ecosystems. However, the majority of the studies consider higher levels of these chemicals and single exposure effects to investigate their potential risks, rather than using environmentally relevant concentrations and their binary mixture. In this study, the toxicity of TCS and TCC, and their binary mixture was assessed in catfish embryos (Rhamdia quelen, a south American native species) exposed to environmental concentrations during 96 h. Organisms were evaluated through the endpoints of developmental abnormalities (spine, fin, facial/cranial and thorax), biochemical biomarkers related to oxidative stress responses: catalase (CAT), superoxide dismutase (SOD), glutathione-S-transferase (GST) activities, protein carbonylation (PCO) and neurotoxicity by acetylcholinesterase activity (AChE). The data showed that TCS caused fin abnormalities, decrease of SOD activity and increase of AChE activity in the catfish embryos of 96hpf. On the other hand, TCC and the binary mixture showed a higher abnormality index for the 96hpf embryos, and an induction of CAT and GST activities for the mixture treatment. The results obtained were able to show potential, but not severe, toxicity of TCS and TCC even in low concentrations and a short period of exposure. The relevance of studies approaching real scenarios of exposure should be reinforced, considering environmental concentrations of chemicals, interactions of contaminants in complex mixtures and the use of a native species such as R. quelen exposed during initial stages of development.

Urban effluents affect the early development stages of Brazilian fish species with implications for their population dynamics

The pollution from urban effluents discharged into natural waters is a major cause of aquatic biodiversity loss. Ecotoxicological testing contributes significantly to understand the risk of exposure to the biota and to establish conservation policies. The objective of the current study was to assess the toxicity of a river highly influenced by urban effluents (Atuba River, Curitiba city, Southern Brazil) to the early stages of development in four South American native fish species, investigating the consequences at the population level through mathematical modelling. The species chosen were Salminus brasiliensis, Prochilodus lineatus, Rhamdia quelen, and Pseudoplatystoma corruscans, ecologically important species encompassing different conservation statuses and vulnerability. The embryos were exposed from 8 to 96 h post fertilization to the Atuba River water, collected downstream of the largest wastewater treatment plant in the Metropolitan Region of Curitiba, and their survival rates and deformities were registered. The species S. brasiliensis and P. lineatus presented the highest mortality rates, showing high sensitivity to the pollutants present in the water. According to the individual-based mathematical model, these species showed high vulnerability and risk of extinction under the tested experimental conditions, even when different sensitivity scenarios of juveniles and adults were considered. The other two species, R. quelen and P. corruscans, showed a more resistant condition to mortality, but also presented high frequency and severity of deformities. These results emphasize the importance of testing the sensitivity of different Brazilian native species for the conservation of biodiversity and the application of models to predict the effects of pollutants at the population level.

Low concentration of 2,4,6-tribromophenol (TBP) represents a risk to South American silver catfish Ramdia quelen (Quoy and Gaimard, 1824) population

The 2,4,6-tribromophenol (TBP) is an environmental persistent pollutant widely used as flame retardant, antimicrobial and insecticide agent in wood preservation and plastic production. Currently, TBP is found in environmental compartments such as soil, freshwater, groundwater, sewage sludge and domestic dust, but the effects to biota and the risk of exposure to aquatic vertebrates are still scarce. In the present study, Rhamdia quelen fish embryos (8 h post-fertilization - hpf) were exposed to 0.3 and 3.0 μg L^-1 of TBP until 96 hpf. Biochemical biomarkers, hatching, survival and larvae/embryo malformations were evaluated after exposure. Additionally, a mathematical model was proposed to evaluate the effects along further generations. The results showed that TBP decreased the survival level but did not cause significant difference in the hatching rates. After 72 and 96 hpf, individuals from the highest tested concentration group showed more severe malformations than individuals from control and the lower concentrations groups. The deformities were concentrated on the embryos facial region where the sensorial structures related to fish behavior are present. The biochemical biomarkers revealed both oxidative stress and neurotoxicity signs after exposure to the contaminant, while the application of the mathematical model showed a decrease of population in both tested TBP concentrations. In conclusion, the current results demonstrated that TBP is toxic to R. quelen embryos and represents a risk to population after early life stage exposure.

Microcystin and pyriproxyfen are toxic to early stages of development in Rhamdia quelen: An experimental and modelling study

The recent increase of freshwater eutrophication has favored cyanobacteria blooms and consequently the increase of toxins such as microcystin-LR in aquatic environments, but few is know about the associated effect of toxin and other compounds. Pyriproxyfen is an insecticide indicated by WHO (World Health Organization) to control Aedes aegypti mosquito (vector of Dengue, Chikungunya and Zika diseases), however, the effects are not well described to non-target species, such as fish. The early life stages (ELS) of fish are more sensitive to chemical stress due to higher metabolic rate, immature immune system and high superficial area/volume ratio. In the current study, ELS of R. quelen a Neotropical fish were exposed to environmentally realistic concentrations of microcystin (1, 10 and 100 µg L^-1_; M1, M2 and M3 groups, respectively) from an algal extract, pyriproxyfen (1 and 10 µg L^-1, P1 and P2) and their association (co-exposure). The hatching, survival and larvae deformities were analyzed, and applied a mathematical model to evaluate the effects on the population size along further generations. Both compounds were toxic to embryos/larvae of fish, but the effects were more pronounced in M2, P1M2 and P2M1 for hatching and M2, P1M2, P2M1 and P1 for survival. Deformities prevailed in groups exposed to the chemicals at 48 hpf (hours post-fertilization) were suggestions of toxicological interaction in P1M2, P2M1 and P2M2 at 48 and 72 hpf. In 96 hpf, the levels of deformities were lower than in previous times. Model predicted population density over 100 years decreased to lower than 0.5 (50%) in all groups, except for P1M1, indicating risk of extinction. P1M2 had the worse results, followed by M2, P1M3 and P2M1. Cyanobacterial blooms can lead to microcystin-LR levels higher than M2 (10 µg L^-1), and the suggestion of toxicological interaction with pyriproxyfen is relevant because both compounds may potentially coexist in aquatic environments. Finally, mathematical models may provide an ecological interpretation of the risk of exposure of fish.

Accidentally catching of the catfish Lophiosilurus alexandri (Steindachner, 1876) larvae in aquariums with different colors

The aim of this study was to evaluate the effect of different colors in development and survival of catfish Lophiosilurus alexandri larvae, as well as over the visual ability of the handler. Larvae were placed in 5 L-aquariums at a density of 7 larvae L-1 , and aquariums had different colors, and were: green and blue (light colors); brown and black (dark colors). The final development; survival, total and standard length, weight and biomass of the larvae were similar in all colored aquaria. The highest mortality occurred during the first days after hatching, declining over the period, when it is observed the larval development, indicating that care should be necessary in the first few days. During cleaning handling, the accidental catch of larvae was higher in black aquariums. In the first days of life, due to the fragility of the larvae, it is possible to verify that between the second and third day occur the greatest mortalities. The number of accidentally captured larvae was lower than the mortality, suggesting that the high mortality in early larval life is not influenced by the handler management. The catfish L. alexandri larvae should be cultivated in aquariums that allow a good contrast between the larvae and the background, to avoid accidental capture of larvae by the handler. It is suggested to avoid the use of dark and black aquariums.

An embryonic staging series up to hatching for Cyprinodon variegatus: An emerging fish model for developmental, evolutionary, and ecological research

Using multiple taxa to research development is necessary for making general conclusions about developmental patterns and mechanisms. We present a staging series for Cyprinodon variegatus as a basis for further study of the developmental biology of fishes in the genus Cyprinodon and for comparative work on teleost fishes beyond the standard models. Cyprinodon are small, euryhaline fishes, widely distributed in fresh, brackish, and hypersaline waters of southern and eastern North America. Cyprinodontids are closely related to fundulids, providing a comparative reference point to the embryological model, Fundulus heteroclitus. Ecologists and evolutionary biologists commonly study Cyprinodon, and we have been using Cyprinodon to study skull variation and its genetic basis among closely related species. We divided embryonic development of C. variegatus into 34 morphologically identifiable stages. We reference our staging series to that already defined for a related model species, Oryzias latipes (medaka) that is studied by a large community of researchers. We provide a description of the early chondrogenesis and ossification of skull and caudal fin bones during the latter stages of embryonic development. We show that Cyprinodon are tractable for studying development. Eggs can be obtained easily from breeding pairs and our study provides a staging system to facilitate future developmental studies.

Embryo toxicity assay in the fish species Rhamdia quelen (Teleostei, Heptaridae) to assess water quality in the Upper Iguaçu basin (Parana, Brazil)

The Iguaçu River is one of the largest and most important rivers in the Southern of Brazil. The Upper Iguaçu Basin is responsible for water supply (80%) of the Metropolitan Region of Curitiba (MRC). After crossing a large urban region, the river is polluted by domestic and industrial sewage, but despite of that few ecotoxicological studies have been performed in order to evaluate the water quality from Iguaçu River. The aim of the present study was to investigate the risk of exposure of Iguaçu water to biota and also human population. In this terms, was utilized the survival effect and the morphological deformities in larval embryos of Rhamdia quelen, a native South America species. The results showed a high level of pollution in all studied sites along the Upper Iguaçu River including PAHs and toxic metals such as lead. The lethal and non-lethal effects described in earlier stages of development suggest an elevated risk to biota. This data was corroborated by the theoretical model, showing that the pollutants present in water from Iguaçu River may further reduce the fish population density including risk of local extinction. The present study reflect the needs to conduct in-depth research to evaluate the real impact of human activities on the endemic fish biota of Iguaçu River including the risk for human populations.

Synchronizing developmental stages in Neotropical catfishes for application in germ cell transplantation

The aim of this study was to describe the effect of temperature on the fertilization, early developmental stages, and survival rate of two Neotropical catfishes Pimelodus maculatus and Pseudopimelodus mangurus. After fertilization, the eggs were incubated at 22°C, 26°C, and 30°C, which resulted in fertilization rates of 96.95 ± 1.79%, 98.74 ± 0.76%, and 98.44 ± 0.19% for P. maculatus and 96.10 ± 1.58%, 98.00 ± 0.63%, and 94.60 ± 2.09% for P. mangurus, respectively. For P. maculatus, hatching occurred after 22 h 30 min post-fertilization at 22°C, 16 h 30 min at 26°C, and 11 h 20 min at 30°C, and the hatching rates were 43.87 ± 7,46%, 57.57 ± 17.49%, and 53.63 ± 16.27%, respectively. For P. mangurus, hatching occurred after 28 h 30 min post-fertilization at 22°C and 17 h 30 min at 26°C with respective hatching rates of 45.4 ± 21.02% and 68.1 ± 12.67%. For this species, all embryos incubated at 30°C died before hatching. Additionally, for P. maculatus, the larvae from the lower (22°C) and higher temperatures (30°C) presented increased abnormality rates, as observed in the head, tail and yolk regions. The lowest abnormality rate was detected at 26°C, which was considered the optimal incubation temperature for both species. The developed protocol enables the manipulation of embryonic development, which is important for the application of reproductive biotechniques, including chimerism and chromosome-set manipulation. The data obtained here are also important for the surrogate propagation of this species as P. mangurus was recently categorized as an endangered fish species.

The effect of temperature on the initial development of Brycon amazonicus Spix & Agassiz, 1829 as tool for micromanipulation of embryos

Primordial germ cell (PGC) transplant is a promising tool in aquaculture; however, successful use of this technique requires in depth knowledge of the early stages of embryo and larval development. The aim of this study was to analyse the effect of different temperatures (22, 26, and 30°C) on the early development of B. amazonicus. The newly fertilized eggs were distributed into tanks with controlled temperature and oxygenation. Samples were collected at pre-established times and analysed under light and fluorescence microscopy. Temperature influenced the speed and duration of each stage of early development, including hatching time. The highest pronuclei fusion rate was observed 8 min post-fertilization (mpf) at 22 and 26°C, and 6 mpf at 30°C. The duration of the 512–1000 blastomeres phase during in the blastocyst stage was 1 h 30 min at 22°C, and 25 min at 26 and 30°C. Hatching occurred at 24 h 30 mpf at 22°C, 16 h post-fertilization (hpf) at 26°C, and 11 h 30 mpf at 30°C. The rate of morphologically normal larvae was 88.34% at 22°C, 90.49% at 26°C, and 73% at 30°C. Malformations of the head, yolk sac, heart, and tail were observed in all temperatures. Nevertheless, B. amazonicus embryos were able to develop satisfactory in all three temperatures tested. These results enable embryo manipulation at different temperatures to optimize the micromanipulation time of embryos and larvae for biotechnological studies.

Assessment of the oxidative and neurotoxic effects of glyphosate pesticide on the larvae of Rhamdia quelen fish

The aim of this work was to investigate the effects of glyphosate on the antioxidant system, as well as the neurotoxic effects on the larvae of Rhamdia quelen. A completely randomized design was implemented with the eggs of silver catfish distributed in 48 containers with 300 mL of water, which were subdivided randomly into two groups: control and treated with 6.5 mg L of glyphosate. These groups were evaluated at four time points (12 h, 24 h, 48 h, and 72 h), each with six replications. The survival rate of eggs/larvae (%) was evaluated, and samples were collected for antioxidant system analysis (catalase - CAT, glutathione transferase - GST, glutathione reductase - GR, and lipoperoxidation - LPO), and neurotoxic evaluation (cholinesterase - ChE). Throughout the 72 h of experimentation, there was a higher survival rate among the animals treated with glyphosate. The highest value of integrated biomarkers response (IBR = 1.26) was at 12 h, presenting induction of the cholinesterase (ChE) enzyme and GR. At 24 h, the value of IBR was -2.56, with inhibition of ChE and induction of GR. At 48 h, the value was -0.76, with induction of LPO. The lowest value of IBR was at 72 h (-4.65), with induction of GST and inhibition of all other biomarkers. Finally, it was possible to detect an acute effect of glyphosate throughout the early development of R. quelen, with a decrease in the antioxidant system control and neurotoxic effects.

Morphology of gametes, post-fertilization events and the effect of temperature on the embryonic development of Astyanax altiparanae (Teleostei, Characidae)

The aim of this study was to describe the morphology of gametes, post-fertilization events and subsequent temperature effects on the early developmental stages of the neotropical species Astyanax altiparanae. The sperm of this species presents a typical morphology of teleost sperm with a spherical head (diameter = 1.88 µm), midpiece (diameter = 0.75 µm) and a single flagellum (length = 18.67 µm). The extrusion of the second polar body and fusion of male and female pronucleus were reported for the first time in this species. Additionally, we observed the formation of the fertilization cone, which prevents polyspermic fertilization. Developmental stages at 22°C, 26°C and 30°C gave rise to fertilization rates at 91.12, 91.42 and 93.04% respectively. Hatching occurred at 25 hpf at 22°C, 16 hpf at 26°C and 11 hpf at 30°C and the hatching rates were 61.78%, 62.90% and 59.45%, respectively. At 22°C, the second polar body was extruded at ≈6 mpf and the male and female pronucleus fused at ≈10 mpf. This fundamental information is important for the field and opens up new possibilities in fish biotechnology, including micromanipulation and chromosome-set manipulation.

R. Neto R, Andrade ES, Andrade EA. Toxicity of cryoprotectants on Prochilodus lineatus (Valenciennes, 1837) (curimba) embryos in an experimental incubator (Characiformes: Prochilodontidae)

This paper investigated the effect of cryoprotectant substances on Prochilodus lineatus embryos in an experimental incubator. The prospective study applied combinations of polyvinyl alcohol, hydroxyethyl cellulose, gelatin and fetal bovine serum with dimethyl sulfoxide and ethylene glycol in a new experimental incubator. The morphology of embryos, larval viability and the efficiency of experimental incubators in maintaining the quality of embryos were evaluated. This study demonstrates the efficient association between hydroxyethylcellulose and dimethyl sulfoxide as greater viability (p<0.05) was found for embryos (72.9 ± 23.9%). It should also be noted the permeation of cryoprotectants in embryos through the changes found in chorion diameter, embryo diameter and embryo volume comparing the treatments versus control group (water) (p<0.05), this results can help in future cryopreservation protocols. Although the temperature and oxygenation differed between the usual and experimental incubators (p<0.05), the results showed a high fertilization rate (79.6 ± 13.2%) for experimental incubators (p<0.05) which is sufficient for the maintenance of embryos in a cryoprotective environment and effectively allows experimentation for long periods with cryoprotectant substances. Cryopreservation of fish embryos has not been accomplished yet and new approaches are required for understanding the permeability of teleost embryos, especially in Brazilian native species.

Structural analysis of embryogenesis of Leiarius marmoratus (Siluriformes: Pimelodidae)

Embryological studies in fish species are useful to the understanding of their biology and systematics. The available biological data in Leiarius marmoratus are scarce and additional information about its reproductive biology is needed, mainly because this species has been commercially exploited and used in production of hybrid lineages. In order to evaluate the temporal–morphological embryonic modifications in L. marmoratus, samples of nearly 200 embryos were collected at random at different stages of development, starting from fecundation (time zero). Embryos were fixed in modified Karnovsk's solution and 2.5% glutaraldehyde, processed and analysed under optic and electron microscopy. The incubation period of L. marmoratus was equal to 14.42 h at a mean temperature of 28.3 ± 0.07°C. The following stages of embryonic development were established: zygote, cleavage, gastrula, organogenesis and hatching. These stages were divided into phases, as follows: cleavage – phases of 2, 4, 8, 16, 32 and 64 cells and morula; gastrula – phases of 25, 50, 75 and 90% of epiboly and blastopore closure; and organogenesis – neurula, segmentation and pre-larval phases. The embryogenesis of L. marmoratus was typical of neotropical teleosteans, with peculiarities in species development.

Ontogenetic development of Heterocharax macrolepisEigenmann (Ostariophysi: Characiformes: Characidae) with comments on the form of the yolk sac in the Heterocharacinae

Fishes in early developmental stages frequently have morphological features that differ from those of adult stages, and many characters found later in ontogeny are not available in initial stages. Hence, morphological descriptions of early stages are useful to provide information for the identification of eggs and larvae, a knowledge still restricted among Neotropical fishes. We studied the development of Heterocharax macrolepis, a heterocharacine whose adult specimens from the aquarium trade were kept and spawned at around 23-24ºC. A developmental series of 51 specimens was preserved, ranging from 3.2 mm notochord length to 18.6 mm standard length, covering approximately the first 73 days post-hatching. We described the development of main morphological features emphasizing those useful in the identification of H. macrolepislarvae (i.e., appearance of preopercle spine and development of the pseudotympanum). We also compared H. macrolepis with photographs taken of live larval specimens of Gnathocharax steindachneri, recently included in the Heterocharacinae. Both species have a yolk sac with a small rounded projection directed posteroventrally. Although this information is not yet available for all pertinent taxa, the different yolk sac shape in other representatives of the Characiformes may indicate that this peculiar yolk sac represents an additional synapomorphy of the Heterocharacini.

Induced spawning and early ontogeny in hatchery-reared catfish Zungaro jahu (Siluriformes: Pimelodidae)

Hatchery-kept catfish jahus Zungaro jahu (Ihering, 1898) were induced to spawn with carp pituitary extract. The telolecithal eggs were round (1.6 ± 0.1 mm in diameter), demersal, free, and covered with a 0.4 mm-thick jelly coat. The gonadosomatic index of 2.8 was comparable to that of other Pimelodidae. The number of eggs x g of ova-1 was 804 ± 144. Hatching occurred 14.5 h after fertilization, at a temperature of 27.3 ± 0.4º C. The newly-hatched embryos measured 3.9-4.3 mm of total length (TL). At 18 h post-hatching (HPH; 5.3 ± 0.1 mm TL), the retina was pigmented, the mouth opened and dorsoflexion of the notochord had initiated. At 36 HPH (6.4 ± 0.2 mm TL), fusiform chromatophores were vertically arranged in the primordial fin fold and the notochord was dorsoflexed. The yolk sac was almost exhausted by 48 HPH (7.3 ± 0.2 mm TL). At 128 HPH (8.6 ± 0.6 mm TL) the pectoral, dorsal, adipose, caudal, anal, and pelvic fins were readily observable whereas the primordial fin fold was no longer visible. At 224 HPH (16.6 ± 2.5 mm TL), the metamorphosis was completed and the larvae had acquired the juvenile appearance.

Early development of Brycon orthotaenia (Pisces: Characidae)

Brycon orthotaenia is an important fish for commercial and sport fishing and may reach 7 kg in body weight; it is endangered in some regions of Brazil's São Francisco River Basin. Breeders were subjected to spawning induction to analyse the early development; oocytes and semen were obtained by manual extrusion and fertilization was carried out using the dry method. After fertilization, eggs were kept in incubators at 24°C. Egg samples were collected every 10 min until hatching in order to monitor embryonic development and were analysed and photographed. Larvae samples were collected daily until the seventh day to analyse the larvae development; larvae were fixed in Bouin's fluid and subjected to routine histological and histochemical techniques for glycoprotein and glyco-conjugated detection. Oocyte extrusion occurred 6 h after the second hormone dose at 26°C. The recently extruded oocytes were spherical, dark green and non-adhesive, with a diameter of 1479.67 ± 53.18 and 3094.60 ± 80.34 μm after hydration. The blastopore closure occurred within 7 h 30 min of fertilization and the fertilization rate was 50.0 ± 5.5 % at 24°C. Embryonic development was completed within 21 h 30 min of fertilization. Complete yolk sac resorption and mouth opening occurred on the third day after hatching, at which time an adhesive organ with mucosubstances was observed. On the third day, an olfactory chamber with cilia and intense cannibalism amongst the larvae was observed. The complete differentiation of the digestive system occurred on the fifth day and the nervous and sensorial systems differentiation occurred on the sixth to seventh days.