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

Abstract 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.Resumo Antecedentes: O cultivo monossexo feminino é desejável na aquicultura comercial de determinadas espécies devido à maior taxa de crescimento. Idealmente, as fêmeas devem ser livres de hormônios exógenos. O passo inicial para gerar descendências femininas livres destes hormônios é a masculinização de fêmeas normais para produzir animais revertidos sexualmente, os chamados neomachos. Os neomachos podem então ser cruzados com fêmeas normais para a produção de descendências femininas. Objetivo: Masculinizar larvas de R. quelen utilizando o hormônio 17α-metiltestosterona (MT) incorporado no alimento. Métodos: 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 pós-eclosão, 30 peixes de cada grupo de tratamento foram eutanasiados para avaliação gonadal através de técnicas histológicas. Resultados: O uso de MT afetou significativamente a diferenciação das gônadas femininas nas doses 60 e 80 mg/kg de alimento. A reversão 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. Gônadas intersexuais foram observadas somente nos tratamentos masculinizantes. Nas maiores doses de MT, efeitos inibitórios de desenvolvimento gonadal foram observados em fêmeas e machos. Conclusão: A administração dietética de MT efetivamente masculinizou larvas de R. quelen. No entanto, a dose mais baixa de 60 mg/kg de alimento é recomendada devido aos efeitos inibitórios das doses mais elevadas de MT no desenvolvimento gonadal de ambos os sexos.Resumen Antecedentes: Debido a su mayor tasa de crecimiento, la producción de peces femeninos monosexo es deseable en acuicultura comercial de determinadas especies. Idealmente, las hembras deben estar libres de hormonas exógenas. El paso inicial para generar descendencia femenina libre de hormonas es la masculinización de hembras genéticas para producir animales sexualmente revertidos, llamados neomachos, los cuales se aparean luego con hembras genéticas para producir descendencia femenina. Objetivo: Masculinizar larvas de Rhamdia quelen con 17α-metiltestosterona (MT) incorporada en el alimento. Métodos: Larvas de R. quelen fueron alimentadas con dietas suplementadas con 60, 80 y 100 mg de MT/kg de alimento durante 21 días. Un grupo control recibió la misma dieta, sin MT. A los 150 días pos-eclosión, 30 peces de cada tratamiento fueron eutanasiados para evaluación gonadal mediante técnicas histológicas. Resultados: La MT afectó significativamente la diferenciación de las gónadas femeninas en las dosis de 60 y 80 mg MT/kg de alimento. El cambio de sexo se observó 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 masculinización se observaron gónadas intersexuales. En las dosis más altas de MT se observó inhibición del desarrollo gonadal de hembras y machos. Conclusiones: El suministro dietario de MT masculinizó 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

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

Abstract 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

Spatiotemporal variations of the ichthyofaunal structure accompanying the seabob shrimp, Xiphopenaeus kroyeri (Crustacea: Penaeidae), fishery in important fishery areas of the Santa Catarina shore, Brazil

The present study analyzed qualitatively and quantitatively the temporal and spatial changes in the fish assemblages present in seabob shrimp distribution sites in two important fishing areas of the Santa Catarina coast. Monthly bottom trawls, conducted between March 2007 and February 2008 in Balneário Barra do Sul and Penha, yielded a total of 38,608 specimens belonging to 54 species, of which 35 occurred in both regions. The Sciaenidae was the most represented family in both number of species and abundance of individuals. The dominant species were Stellifer rastrifer (Jordan, 1889), S. brasiliensis (Schultz, 1945), Paralonchurus brasiliensis (Steindachner, 1875), Isopisthus parvipinnis (Cuvier, 1830), Trichiurus lepturus (Linnaeus, 1758), and Pellona harroweri (Fowler, 1917). The ichthyofaunal structure showed a spatiotemporal dependence with significant differences in March 2007 and January and February 2008 between Balneário Barra do Sul and Penha. The main differences were attributed to dominant species, which were responsible for significantly altering the abundance of the assemblages. The species richness was similar in both sites, whereas the diversity and equitability indices showed monthly fluctuation patterns that differed between Balneário Barra do Sul and Penha. The Shannon index differed in August, September and November 2007 and January and February 2008, with an H' ranging from 0.74 to 1.98 influenced by dominant species, whereas significant variations were observed for the Pielou index in November 2007 and February 2008. The Berger-Parker index demonstrated a clear dominance pattern where the monthly numeric contribution of a single species ranged from approximately 30 to 80%. Although the results showed differences between fishing grounds 25% of the time, we conclude that fish assemblies captured as accompanying fauna in artisanal seabob shrimp fisheries showed statistically similar characteristics for most of the year, although Balneário Barra do Sul and Penha are 35 km away from each other