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Una alternativa para reducir el uso de hormonas con aplicación inmediata en el cultivo comercial de la tilapia del Nilo, es la evaluación precisa de los tiempos de masculinización en variedades domesticadas. El objetivo del trabajo fue evaluar el porcentaje de masculinización y el crecimiento obtenido en la tilapia del Nilo alimentada con alimento comercial adicionado con 17α- metiltestosterona a diferentes tiempos. Para ello se evaluaron cinco tiempos (0, 10, 15, 20 y 25 días) de administración de hormona a una población mixta de tilapia del Nilo variedad Spring. Para cada tratamiento se utilizaron tres réplicas. Los alevines fueron sembrados a densidad de 0.5 alevines L−1 en un sistema de recirculación cerrado. El cultivo consistió de 30 días en acuarios de acrílico de 85 L y 20 días en tanques exteriores de 1000 L. La determinación del sexo se realizó con la técnica de squash. El crecimiento se determinó por medio del peso húmedo y la longitud total obtenida de las biometrías. Los resultados indican una masculinización del 100% desde los 10 días de aplicación del esteroide, pero los mayores valores de crecimiento se observaron en los grupos que recibieron el esteroide por mayor tiempo. Los resultados muestran que no es necesario administrar el esteroide durante 30 días para lograr una masculinización del 100% en variedades domesticadas y que el esteroide tiene efecto positivo en la tasa de crecimiento de los alevínes, persistiendo por algunas semanas después de terminado el tratamiento.

Sex-reversal by exogenous hormones is the most common technique used to generate monosex populations of Nile tilapia (Oreochromis niloticus). However, this technique has provoked a negative perception in recent years. Because of this, alternative techniques have been developed, including the production of YY males. Although the nal product (for sale) is not administered hormones, the rst part of this technique still requires the feminization of XY fry by use of estrogens, including some of a synthetic nature, such as diethylstilbestrol (DES), an estrogen that has shown particularly excellent results in related species. The aim of this study was to evaluate the eect of increasing concentrations of DES (100, 200, 300, and 400 mg kg−1 ) during the fry stage on the sex proportion, growth and gonadosomatic index (GSI) of Nile tilapia. The 400 mg kg−1 concentration was the one that produced the highest proportion of females (91 %). However, increasing the concentration of DES provided through diet does not guarantee a 100 % feminization rate. Additionally, the growth, survival and GSI, showed a signicant decrease (p < 0.05) in all groups fed with DES compared to the control group. It is possible that the anabolic eect of DES observed in other species is not present in Nile tilapia

Background. Nile tilapia (Oreochromis niloticus) is one of the most important species worldwide for aquaculture; however, the use of steroids to masculinize large volumes of fry is seen negatively by the market and environmental groups. The use of the progeny of YY males is a recent alternative that, in theory, allows to maintain the same yields, with the advantage of marketing a product free of hormones. Objective. To evaluate the performance during growth, the gonadosomatic index, the biochemical composition, as well as the percentage of males obtained in the progeny of YY males and compare them against those obtained in a commercially masculinized progeny using flouxymesterone. Methodology. Juveniles produced from a YY male and masculinized juveniles were stocked in external tanks of 3 m2 (in triplicate) and were cultivated for 105 days following a commercial type feeding protocol. Results. No significant differences were detected between both progenies with respect to productive performance during growth, including fillet yield. However, the progeny of YY males showed significantly higher values (P < 0.05) of moisture, ashes and lipids in muscle, as well as in the gonadosomatic index, probably due to the presence of a small percentage of females (8%). Implications. The study contributes to the insertion of YY technology into the commercial culture of Nile tilapia. Conclusion. The performance shown by the progeny of YY males compared to that of a masculinized line is similar in terms of growth, yield and survival; therefore, its implementation in the region could reduce production costs and environmental contamination, thanks to the reduction in the use of hormones.

Sex-reversal by exogenous hormones is the most common technique used to generate monosex popu- lations of Nile tilapia (Oreochromis niloticus). However, this technique has provoked a negative perception in recent years. Because of this, alternative techniques have been developed, including the production of YY males. Although the final product (for sale) is not administered hormones, the first part of this technique still requires the feminization of XY fry by use of estrogens, including some of a synthetic nature, such as diethylstilbestrol (DES), an estrogen that has shown particularly excellent results in related species. The aim of this study was to evaluate the effect of increasing concentrations of DES (100, 200, 300, and 400 mg kg−1 during the fry stage on the sex proportion, growth and gonadosomatic index (GSI) of Nile tilapia. The 400 mg kg−1 concentration was the one that produced the highest proportion of females (91 %). However, increasing the concentration of DES provided through diet does not guarantee a 100 % feminization rate. Additionally, the growth, survival and GSI, showed a significant decrease (p < 0.05) in all groups fed with DES compared to the control group. It is possible that the anabolic effect of DES observed in other species is not present in Nile tilapia.