Levels of 17-methyltestosterone in different temperatures on sex inversion of Nile tilapias Oreochromis niloticus. / NÃveis de 17-α metiltestosterona em diferentes temperaturas na inversÃo sexual de tilÃpias- Oreochronis niloticus

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Due to sexual precocity and higher growth rate of Nile tilapia males in relation to females, several techniques on sex inversion, more specifically the masculinization or production of mono-sex populations, have been praised. Among the techniques used for sex inversion in tilapias, the most disseminated around the world and Brazil is the hormone usage incorporated to ration, mainly 17-methyltestosterone. In despite of it has been demonstrated that hormone usage does not result in residues accumulation in treated fish tissues, there still are concerns about its release in environment and consumers response. Therefore, the objective of this work is to evaluate the sex inversion technique using 17-methyltestosterone (MT) hormone, combined with temperature modification of tilapia larvae storage, aiming at the decrease of hormonal dosage normally employed, reducing an environmental impact which the hormone usage could cause. The experiment was performed at UFLA Fish Culture Station, using tilapia after-larvae obeying a totally randomized experimental delineation in a factorial scheme 4x4, in 4 temperatures (26Â, 28Â, 30Â, 32ÂC) and 4 hormonal doses (0, 20, 40, 60mg of MT/kg of ration) during 28 days, with 5 repetitions. In order to determine tilapias sex inversion, gonads histological analysis was performed, beyond manual sexing. As temperature raised, weight gain rate, size and survival increased (p<0,01); however, this temperature raise was not effective in modifing males ratio (p>0,01), which occurred only due to the used hormone treatment. The dose of 40mg of MT/kg of ration provided similar results to those of 60mg of MT/kg of ration. Hence, the temperature band from 26Â to 32ÂC does not affect sex inversion rate, but temperature around 30ÂC improves the performance of tilapias related to the growth and survival. The dose of 40 mg of MT/kg of ration is enough to achieve mono-sex populations.

ASSUNTO(S)

temperatura. inversÃo sexual zootecnia tilÃpia tilapia, sex inversion, temperature

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