South American Catfish Research Articles

Descriptive analysis of the sperm of three South American catfish species maintained ex situ and the influence of morphology on sperm movement

Descriptive analysis of the sperm of three South American catfish species maintained ex situ and the influence of morphology on sperm movement

Protocols for the seminal cryopreservation of South American catfishes – current status

Protocols for the seminal cryopreservation of South American catfishes – current status

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.

Polygynandry and high genetic diversity supported by kinship and population genetics from neotropical catfish ichthyoplankton

AbstractKnowledge about reproductive biology is critical for understanding species ecology and evolution, hence their conservation. However, such information remains elusive for many species due to the difficulty of observing mating in nature. Herein, we coupled population and sociogenetic analysis to assess the reproductive biology of an important South American catfish, the “painted catfish” Pimelodus maculatus. We analysed the genetic diversity and kinship patterns of three wild ichthyoplankton samples identified by DNA barcoding and screened with microsatellite loci. We found the same trend in the three samples analysed: a high number unrelated larvae (r < 0.25) and potential parents involved (Ca1, 24♀:24♂; Ca2, 21♀:23♂; Cin, 24♀:25♂), as well as a high number of familial clusters (ML: 19‐21; MCMC: 23‐26). The data indicate a parental sexual proportion close to 1:1 and a polygynandrous mating system. We found high levels of genetic diversity, low GST values (GST < 0.014), but moderate DEST values between the tributary and reservoir samples (DEST > 0.25; Cin x Ca1 or Cin x Ca2), a similar pattern to the observed in adult populations. These results indicate that the mating system of P. maculatus has played an important role in minimising the loss of genetic diversity, a condition that may have favoured the species in a highly fragmented landscape.

Fermentation of Soybean Meal with Lactobacillus acidophilus Allows Greater Inclusion of Vegetable Protein in the Diet and Can Reduce Vibrionacea in the Intestine of the South American Catfish (Rhamdia quelen).

Simple SummaryThere is a demand to replace fishmeal with protein sources of plant origin in fish feeds. Biotechnology strategies, such as fermentation, can improve the bioavailability of plant proteins and decrease the presence of antinutrients, optimizing the results obtained. Fermented soybean meal has already been evaluated for different fish species as a replacement for fishmeal, and there is evidence that it can improve the intestinal health of animals. Lactobacillus acidophilus is a strain used as a probiotic in fish feeding but it remains to be evaluated as a potential fermentation bacterium for feed ingredients. This study aimed to evaluate the effect of diets containing different inclusion levels (0%, 7%, 14%, 21% and 28%) of soybean meal fermented by L. acidophilus (SMFL) on the zootechnical performance and intestinal health of South American catfish juveniles (Rhamdia quelen). The inclusion of SMFL up to 21% in replacement of fish meal did not affect the zootechnical performance of fish and also decreased the concentration of Vibrionaceae bacteria present in the intestine compared to the control group. The results demonstrate that fermentation with L. acidophilus enables greater inclusion of soybean protein in South American catfish diets and promotes the control of intestinal pathogenic bacteria.The objective of this study was to evaluate the effect of diets containing different inclusion levels (0%, 7%, 14%, 21% and 28%) of soybean meal fermented by Lactobacillus acidophilus (SMFL) on the zootechnical performance and intestinal health of South American catfish juveniles (Rhamdia quelen). The experimental design was completely randomized with five treatments and four replications and lasted 56 days. Five isoproteic (39% crude protein) and isoenergetic (4300 kcal of gross energy kg−1) diets were formulated where SMFL was included in replacement of fish meal. Two hundred forty South American catfish juveniles (3.0 ± 0.5 g) were distributed in 20 tanks (70 L) connected in a recirculation aquaculture system. At the end of the experiment, the inclusion of SMFL up to 21% in replacement of fish meal did not affect the zootechnical performance and also decreased the concentration of Vibrionaceae bacteria present in the intestine compared to the control group. The amount of total lactic and heterotrophic bacteria, the enzymatic activity and the intestinal morphometry did not differ between dietary treatments. The results demonstrate that fermentation with Lactobacillus acidophilus enables greater inclusion of soybean protein in South American catfish diets and promotes the control of intestinal pathogenic bacteria.

The use of differential separation and density gradient with AllGrad 90% after thawing improves the sperm quality of South American catfish (Rhamdia quelen)

The use of technologies in assisted reproduction, such as the use of centrifugation, has been reported as a tool that allows separating the best portion of sperm from cryopreserved milt. The main of this work was to compare two separation techniques, differential and density gradient, on thawed Rhamdia quelen milt, based on sperm functionality and fertilization capacity. Three treatments were compared: control, differential centrifugation or pelletization (T1), and density gradient centrifugation (T2). Motility percentage was better for differential (42.58 ± 6.50%) than for the control treatment (32.44 ± 6.03%). Membrane integrity and kinetic parameters was not different between treatments. The presence of normal sperm was higher in T2 treatment (13.55 ± 5.82%) when compared to the control (10.72 ± 3.53%) and T1 (3.97 ± 1.95%). There was a lower rate of morphological tail damage in the T1 (26.91 ± 7.13%) treatment compared to the T2 (37.48 ± 10.81%) and control (45.88 ± 4.84%). For the head morphologies, the lowest percentages were for the control (35.72 ± 5.89%) and T2 (4.89 ± 14.94%) treatments compared to the T1 treatment (62.59 ± 9.67%). In the MTT (3- (4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide) test (AU/100 million sptz), the centrifuged treatments resulted in values of 1.58 ± 0.79 (T1) and 2.02 ± 1.88 (T2), better than the treatment control (0.20 ± 0.08). Likewise, the fertilization and hatching rates, respectly, were better for the T1 (76.68 ± 15.22% and 54.62 ± 17.39%) and T2 (69.85 ± 17.85% and 50.87 ± 20.59%) treatments, than the control treatment (40.03 ± 11.67% and 24.14 ± 13.97%). The comparison of differential centrifugation with density gradient centrifugation was carried out for the first time with cryopreserved milt of R. quelen. In summary, both centrifugation techniques proved to be efficient in obtaining a better portion of functional sperm from thawed milt. This is based on the high rates of embryonic survival and hatching obtained after both differential and density gradient separation.

Revision of the South American catfish genus Hypophthalmus (Siluriformes, Pimelodidae) with descriptions of two new species from the Amazon and Orinoco Basins

The pimelodid genus Hypophthalmus is a small group of pelagic and planktivorous catfishes that are abundant and variously distributed in the lowland river basins of the Amazon, Parnaíba, Orinoco, Guianas and Paraná. Since their earliest published descriptions, commencing over 190 years ago with H. edentatus Spix and Agassiz 1829, the taxonomy and nomenclature of Hypophthalmus species have been confused and unresolved. In this study, four of the six available species names are validated and two new species are described. Newly discovered characters of the vertebral column, circumoral barbels, pelvic fins, and lateralis sensory canals provide strong support and diagnostics for species and species-groups. A key to species, anatomical descriptions, notes on identification of small juveniles and phylogenetic interrelationships are included. A lectotype is designated for Hypophthalmus marginatus and nominal Hypophthalmus longifilis, respectively.

Electrical stunning in South American catfish (Rhamdia quelen) using direct current waveform: welfare and meat quality

ABSTRACT: In Brazil, humane slaughter regulation is in use since 2000; however it is not applied to fish. This paper studied parameters for electrical stunning using direct current waveform in South American catfish (Rhamdia quelen) and its subsequent effects on muscular pH and rigor mortis. Seventy fish were allocated into two groups. In group 125, fish were stunned using 125 Volts (V), 30 Hz, duty cycle of 90% and 1.3 Amp (A) applied for 30 s; in group 400, fish were stunned with 400 V, 30 Hz, duty cycle of 27%, 0.9 A, for 30 s. Unconsciousness time was determined through behavioural assessment. After slaughter, ten fish from each group were refrigerated for both measurements muscular pH and rigor mortis index (RMI) at 0, 3, 6, 24, 72 and 120 h. In 125, 14.4% (5/35) of fish were not effectively stunned, in contrast with 400 in which 100% of fish (35/35) were effectively stunned. The unconsciousness duration was higher in 400 group (87.7±16.1 s) in contrast with group 125 (66.6 ± 16.1 s). Until 6 h post mortem ninety percent of fish reached maximum rigor mortis (RMI=100%).

Protein to energy ratios and cost, performance, and ammonia excretion in juvenile jundiá (Rhamdia quelen), South American catfish

ABSTRACT: The determination of nutritional requirements, based on diets administered in practice, considers physiological specificities and sustainability are essential to the development of suitable aquaculture technologies for novel fish species. The growth of jundia (Rhamdia quelen Quoy and Gaimard) juveniles (31.54 ± 4.92 g) fed five diets comprising increasing levels of digestible protein (DP: 24, 29, 34, 39, and 44 %) and digestible energy (DE: 12.13, 13.39, 13.81, 14.64, and 15.06 MJ kg−1) with DP:DE ratios: 20, 22, 25, 27, and 29 g MJ−1, respectively, was evaluated. Each diet was fed to three groups of 25 fish for 75 days. Regression analysis showed that the different DP:DE ratios affected both growth and economic performance as well as excretion of total ammonia nitrogen. Fish fed diets with DP:DE ratios between 22 and 27 g MJ−1 achieved a higher daily weight gain, superior apparent net protein utilization, feed conversion rates, and lower feed costs. For the economically viable and environmentally friendly farming of jundia juveniles in the initial grow–out stage (30 to 80 g average weight), the best DP:DE ratio was 25 g MJ−1 DP:DE (34.05 % DP and 13.81 MJ kg−1 DE).

A reappraisal of phylogenetic relationships among auchenipterid catfishes of the subfamily Centromochlinae and diagnosis of its genera (Teleostei: Siluriformes)

A hypothesis of phylogenetic relationships is presented for species of the South American catfish subfamily Centromochlinae (Auchenipteridae) based on parsimony analysis of 133 morphological characters in 47 potential ingroup taxa and one outgroup taxon. Of the 48 species previously considered valid in the subfamily, only one, Centromochlus steindachneri, was not evaluated in the present study. The phylogenetic analysis generated two most parsimonious trees, each with 202 steps, that support the monophyly of Centromochlinae composed of five valid genera: Glanidium, Gephyromochlus, Gelanoglanis, Centromochlus and Tatia. Although those five genera form a clade sister to the monotypic Pseudotatia, we exclude Pseudotatia from Centromochlinae. The parsimony analysis placed Glanidium (six species) as the sister group to all other species of Centromochlinae. Gephyromochlus contained a single species, Gephyromochlus leopardus, that is sister to the clade Gelanoglanis (five species) + Centromochlus (eight species). Based on the new taxonomic arrangement herein, BalroglanisGrant 2015 and SauronglanisGrant 2015 are placed in the synonymy of Centromochlus. Tatia is the most diverse genus within Centromochlinae, with twenty-six species in three monophyletic clades. The species composition of Tatia differs from that of Calegari et al. (2019). DuringlanisGrant 2015 and FerrarissoaresiaGrant 2015 are considered synonyms of Tatia. All generic taxa within Centromochlinae are diagnosed based on synapomorphic morphological characters. An identification key for Centromochlinae is provided.

Essential oils of Ocimum gratissimum and Zingiber officinale as anesthetics for the South American catfish Pseudoplatystoma reticulatum

This study evaluated the essential oils of clove-basil (Ocimum gratissimum) and ginger (Zingiber officinale) as anesthetics for the South American catfish Pseudoplatystoma reticulatum and their effects on fish hematology and plasma glucose. For each essential oil, three concentrations were tested (100 mg L−1, 150 mg L−1 and 200 mg L−1) and a control lacking the essential oils was also present. Fish with a mean weight of 40.0 ± 9.9 g were used to provide for 6 replicates per treatment, each fish being a replicate. The times for induction and recovery, as well as the following hematological variables were assessed: Hemoglobin, hematocrit, total number of red blood cells (RBC), total number of white blood cells (WBC), total count of thrombocytes, mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), mean corpuscular hemoglobin (MCH) in addition to plasma glucose. Significant negative relationships (p < .05) were observed between essential oil concentration and induction time, with the O. gratissimum essential oil resulting in lower times. A significant positive relationship (p < .05) between recovery time and essential oil concentration was observed only for the O. gratissimum essential oil. Anesthesia with the O. gratissimum essential oil did not affect the fish hematology and plasma glucose. In contrast, significant relationships were found between the Z. officinale essential oil concentration and hemoglobin, hematocrit and MCHC (p < .05), possibly indicating hemoconcentration. This study demonstrated that both O. gratissimum and Z. officinale essential oils are capable of inducing anesthesia in P. reticulatum, although the former presented better results, considering the lower induction time and the fact that fish hematology was not affected.

Digestible energy, protein, and energy–protein ratio requirements of Pseudoplatystoma reticulatum

AbstractThe use of novel aquaculture species depends on the determination of their nutritional requirements. This study aims at determining dietary protein, energy, and protein–energy ratio requirements of juvenile striped surubim, Pseudoplatystoma reticulatum, an economically important carnivorous South American catfish for capture fisheries and highly regarded for fish farming purposes. Juvenile striped surubim (53.6 ± 1.30 g, n = 525) were randomly stocked (n = 7) in 75 test cages (210 L) and hand fed for 60 days, two daily meals, with 25 diets formulated to contain five levels of digestible protein (DP) (320, 360, 400, 440, and 480 g/kg) and five levels of digestible energy (DE) (15.1, 15.6, 16.1, 16.6, and 17.2 MJ/kg) in a completely randomized design, 5 × 5 factorial scheme (n = 3). Dietary energy and protein level affected performance, feed efficiency, and metabolism while the whole‐body composition was not affected by diets. Estimated dietary requirements for the best performance and best nutrient retention were 15.1 MJ/kg DE and 390 g/kg DP, therefore a 25.9 g/MJ of DP:DE ratio.

Effect Of Glutamine Supplementation On The Cryopreserved Sperm Of South American Catfish

Effect Of Glutamine Supplementation On The Cryopreserved Sperm Of South American Catfish

Gyrodactylus lilianae n. sp. (Polyonchoinea: Gyrodactylidae) from Rhamdia quelen (Quoy & Gaimard) (Siluriformes: Heptapteridae) from southern Brazil: a potential nuisance for aquaculture.

Species of Monogenoidea (Platyhelminthes) are in its majority ectoparasites of marine and freshwater fishes. Many species of the group can promote great economic losses to fish production systems worldwide. The present study describes a new species, Gyrodactylus lilianae n. sp., from the body surface, fins and barbels of a captive South American catfish, Rhamdia quelen (Quoy & Gaimard) (Siluriformes: Heptapteridae) from southern Brazil. The new species is morphologically similar to Neotropical species of Gyrodactylus von Nordmann, 1832 from Siluriformes from which it differs most conspicuously by the morphology of the hook with a pronounced convex heel, somewhat depressed, slightly pointed toe, and a small distal bulb. The identity of the new species is also strongly supported by phylogenetic analysis based on cytochrome c oxidase subunit 2 mitochondrial gene (cox2) sequences and the rDNA fragment ITS1-5.8-ITS2. Infections with the new species in captive R. quelen juveniles were considered the main causative agent of observed mortalities. Tissue damage caused by G. lilianae n. sp. apparently facilitated the occurrence of secondary infections by protists (Ichthyophthirius multifiliis) and bacteria (Aeromonas hydrophila).

Innate response based on visual cues of sympatric and allopatric predators in Nile tilapia

Predators are an important selective pressure for prey, and responses to visual exposure to non-predators and to allopatric and sympatric predators may assist the understanding of how prey animals recognize and distinguish potential threats. Here, we visually exposed predator-naïve Nile tilapia (Oreochromis niloticus) to aquaria with only water (handling-negative control), a non-predator fish (Cyprinus carpio), a South American catfish (Pseudoplatystoma coruscans, allopatric predator), and an African catfish (Clarias gariepinus; sympatric predator). We found that Nile tilapia displayed antipredator responses to both predator catfish but not to non-predator fish or negative control conditions. These antipredator responses, however, were stronger to the sympatric catfish in comparison to the allopatric animal. We concluded that Nile tilapia is able to innately distinguish between a sympatric and an allopatric predator based on visual cues. We assume that the innate recognition of the allopatric predator could be attributed to similarities in the body morphology and movement (key stimuli) of the South American and African catfish. Although this is plausible, the mechanism of the innate allopatric recognition remains unknown and deserves future investigation.

Testicular differentiation and development in South American catfish, surubim, Pseudoplatystoma fasciatum

In the species Pseudoplatystoma fasciatum the males are smaller than females. Thus, the objective of this study was to describe the process of testicular differentiation and provide tools for sex manipulation techniques aimed at improving the productivity of farming of sexually-reversed females. Correlation between the length, age, sex rate and the stage of gonadal development were analyzed in this species from samples collected between 0 and 240 days post-hatching. Testicular differentiation was divided into eight stages, based on the cellular and morphological characteristics of the gonad. The results showed that sexual differentiation has a greater correlation to the size than the age in this species. This study provides knowledge on the proliferation and distinctive arrangement of somatic cells, which enabled the early identification of the testis due to the presence of future fringes in the specimens. Testicular differentiation in P. fasciatum was histologically different from other species due to the proliferation and distribution of somatic cells in the regions that would originate the testicular tubules and sperm ducts. Meiosis began at a later stage in comparison with other species, therefore, it was not considered a criterion for early sexual characterization. It can be concluded that testicular differentiation in P. fasciatum occurs relatively early and this data can be used to improve sex inversion protocols and increase productivity in this species.

Cysteine supplementation on the quality of cryopreserved sperm of south american catfish

Cysteine supplementation on the quality of cryopreserved sperm of south american catfish

Effects of different doses of eugenol on plasma cortisol levels and the quality of fresh and frozen-thawed sperm in South American catfish (Rhamdia quelen)

The production of captive fish is only possible through artificial reproduction, but manipulation is a known stressor stimulus. Thus, the objective of the present study was to evaluate the effects of different eugenol concentrations (0, 30, 40, 50 and 60 mg/L) during reproductive management of Rhamdia quelen. Seventy-five mature male R. quelen were randomly distributed among the five treatments, and blood samples were collected at the time of semen collection to measure plasma cortisol. The following parameters were evaluated in the fresh semen samples: motility, motility duration, concentration and fertilization rate. The following parameters were evaluated in the frozen semen samples: motility, motility duration, morphology, membrane integrity, DNA integrity and mitochondrial functionality. The animals anesthetized with eugenol at concentrations of 40 and 50 mg/L had lower levels of plasma cortisol (88.4 and 83.3 ng/mL, respectively) than the control (147.1 ng/mL). For fresh semen, the control treatment presented the highest rate and time of motility but differed (P < 0.05) only from the animals treated with 60 mg/L eugenol. For the cryopreserved semen the highest rates and motility time were observed in the control treatment and in the animals anesthetized with 40 mg/L eugenol, differing (P < 0.05) from anesthetized animals with 50 and 60 mg/L. Mitochondrial functionality was higher in fish anesthetized with 30 mg/L eugenol differing only for animals anesthetized with 60 mg/L. There was no difference between treatments for sperm concentration and fertilization rate of fresh semen. There were no differences (P > 0.05) between treatments in the parameters of membrane integrity, DNA integrity and% of normal spermatozoa after thawing of the cryopreserved semen samples. The use of 30, 40 and 50 mg/L eugenol maintained the seminal quality of the fresh semen, and the quality of the thawed semen was maintained with 30 and 40 mg/L eugenol. These results show that stress reduction can be reconciled with reproductive management without compromising reproductive performance.

Sardine (Sardinella spp.) protein hydrolysate as growth promoter in South American catfish (Rhamdia quelen) feeding: Productive performance, digestive enzymes activity, morphometry and intestinal microbiology

This study evaluated the effects of dietary inclusion of sardine (Sardinella spp.) protein hydrolysate (SPH) on productive performance, digestive enzymatic activity, morphology and intestinal microbiology of South American catfish (Rhamdia quelen) juveniles. SPH was produced from sardine processing wastes using Protamex® protease complex from Novozymes A/S. Four levels of inclusion were evaluated (0, 2, 5 and 10%). A total of 480 South American catfish juveniles (average weight 11.3 ± 2.46 g) were distributed in 24 polyethylene containers, in a completely randomized design with four treatments and six replications. The fish were fed twice daily until apparent satiation with isoproteic (39%) and isoenergetic (4376 kcal.kg−1) diets for 56 days. Regardless of the SPH inclusion levels in the diets, average weight gains (36.28 g), specific growth rate (2.56% day−1), apparent feed intake (40.51 g) and apparent feed conversion rate (1.12) were improved when compared to the control treatment (average of 24.95 g; 2.11% day−1; 31.00 g and 1.28, respectively). Total alkaline protease activity of the gastrointestinal tract of the South American catfish juveniles was higher in the treatment that received 5% SPH (0.61 ± 0.23 U. mg−1 of protein) than in the control (0.26 ± 0.08 U.mg−1 of protein). The amylase activity was higher in the treatments with 2% SPH (1.58 ± 0.19 U. mg−1 of protein) and 5% SPH (1.43 ± 0.44 U. mg−1 of protein) when compared to the control (0.40 ± 0.18 U. mg−1 of protein). In the 5% SPH treatment, higher amounts of lactic acid bacteria and Vibrionaceae were detected than in the other treatments. No difference was found for total heterotrophic bacteria. There was no difference in the intestinal morphometry of the South American catfish for any one of the analyzed parameters. Inclusion levels of up to 10% SPH in the diets of South American catfish showed improvement in the productive performance and nutritional efficiency, acting as a growth promoter. The inclusion level of 5% SPH caused an increase in the digestive enzymatic activity and populations of intestinal lactic acid bacteria. Thus, a prebiotic effect on the fishes was observed and the inclusion level may determine the effects of SPH.

Masculinization of South American catfish (Rhamdia quelen) through dietary administration of 17α-methyltestosterone

Background: Production of monosex cultures of females is desirable in commercial aquaculture of certain species due to their higher growth rate. Ideally, females should be free of exogenous hormones. The initial step to produce hormone-free all-female offspring is masculinization of normal females to create sex reversed animals, called neomales, which are then be bred with normal females obtaining all-female offspring. Objective: To masculinize Rhamdia quelen fry by adding 17α-methyltestosterone (MT) hormone to the feed. Methods: Larvae of R. quelen were fed diets supplemented with 60, 80, or 100 mg MT/kg feed for 21 days. A control group was fed the same diet free of MT. At 150 days post-hatching, 30 fish of each treatment group were euthanized to evaluate gonadal changes using histological techniques. Results: MT significantly affected the differentiation of female gonads in the 60 and 80 mg MT/kg feed groups. Sex reversal was observed in all MT treatment groups, with 50, 40, and 20% neomales produced with 60, 80, and 100 mg MT/kg feed, respectively. Intersex gonads were observed only in the masculinization treatment groups. Inhibitory effects on gonadal development of females and males were observed at the highest MT doses. Conclusion: Dietary administration of MT effectively masculinizes R. quelen fry; however, the lowest dose of 60 mg/kg feed is recommended, since higher doses have inhibitory effects on gonadal development in both sexes. Keywords: histology, fish gonads, monosex culture, neomales, sex reversal. Resumen Antecedentes: Debido a su mayor tasa de crecimiento, la produccion de peces femeninos monosexo es deseable en acuicultura comercial de determinadas especies. Idealmente, las hembras deben estar libres de hormonas exogenas. El paso inicial para generar descendencia femenina libre de hormonas es la masculinizacion de hembras geneticas para producir animales sexualmente revertidos, llamados neomachos, los cuales se aparean luego con hembras geneticas para producir descendencia femenina. Objetivo: Masculinizar larvas de Rhamdia quelen con 17α-metiltestosterona (MT) incorporada en el alimento. Metodos: Larvas de R. quelen fueron alimentadas con dietas suplementadas con 60, 80 y 100 mg de MT/kg de alimento durante 21 dias. Un grupo control recibio la misma dieta, sin MT. A los 150 dias pos-eclosion, 30 peces de cada tratamiento fueron eutanasiados para evaluacion gonadal mediante tecnicas histologicas. Resultados: La MT afecto significativamente la diferenciacion de las gonadas femeninas en las dosis de 60 y 80 mg MT/kg de alimento. El cambio de sexo se observo en los tratamientos con las dosis de 60, 80 y 100 mg MT/kg alimento, con 50, 40 y 20% de neomachos, respectivamente. En los tratamientos de masculinizacion se observaron gonadas intersexuales. En las dosis mas altas de MT se observo inhibicion del desarrollo gonadal de hembras y machos. Conclusiones: El suministro dietario de MT masculinizo las larvas de R. quelen . Se recomienda usar 60 mg/kg, ya que dosis mayores tienen efectos inhibidores en el desarrollo gonadal para ambos sexos. Palabras clave: cultivo monosexo, gonadas de peces, histologia, neomachos, reversion sexual. Resumo Antecedentes: O cultivo monossexo feminino e desejavel na aquicultura comercial de determinadas especies devido a maior taxa de crescimento. Idealmente, as femeas devem ser livres de hormonios exogenos. O passo inicial para gerar descendencias femininas livres destes hormonios e a masculinizacao de femeas normais para produzir animais revertidos sexualmente, os chamados neomachos. Os neomachos podem entao ser cruzados com femeas normais para a producao de descendencias femininas. Objetivo: Masculinizar larvas de R. quelen utilizando o hormonio 17α-metiltestosterona (MT) incorporado no alimento. Metodos: Larvas de R. quelen foram alimentadas com dietas suplementadas com MT nas doses de 60, 80 ou 100 mg/kg de alimento durante 21 dias. Um grupo controle foi alimentado com dieta similar livre de MT. Aos 150 dias pos-eclosao, 30 peixes de cada grupo de tratamento foram eutanasiados para avaliacao gonadal atraves de tecnicas histologicas. Resultados: O uso de MT afetou significativamente a diferenciacao das gonadas femininas nas doses 60 e 80 mg/kg de alimento. A reversao sexual foi observada em todos os grupos tratados com MT, gerando 50, 40 e 20% de neomachos nas doses 60, 80 e 100 mg MT/kg de alimento, respectivamente. Gonadas intersexuais foram observadas somente nos tratamentos masculinizantes. Nas maiores doses de MT, efeitos inibitorios de desenvolvimento gonadal foram observados em femeas e machos. Conclusao: A administracao dietetica de MT efetivamente masculinizou larvas de R. quelen . No entanto, a dose mais baixa de 60 mg/kg de alimento e recomendada devido aos efeitos inibitorios das doses mais elevadas de MT no desenvolvimento gonadal de ambos os sexos. Palavras-chave: cultivo monossexo, gonadas de peixe, histologia, neomachos, reversao sexual.