Sex reversal in Nile tilapia (Oreochromis niloticus Linnaeus) by androgen immersion

摘要

Two experiments were conducted to investigate the efficacy of three androgens applied through immersion treatments on the sex ratio of Nile tilapia (Oreochromis niloticus L.) fry. In experiment 1, 14 days post-hatching (DPH) larvae were exposed to a single immersion treatment in 17alpha-methyltestosterone (MT), 17alpha-methyldihydrotestosterone (MDHT) or 17alpha-ethynyltestosterone (ET) at 200, 600 and 1800 mug L-1 over 4 h (130 larvae per treatment). In experiment 2, Nile tilapia larvae were exposed to the higher androgen concentration (1800 mug L-1) applied as either a single immersion (14 DPH) or double immersion (10 and 14 DPH) over 4 h (125 larvae per treatment). Change in sex proportion within each experiment as well as between experiments was analysed by the chi-square test. In experiment 1, MT, MDHT and ET were equally effective in significantly increasing the proportion of males when applied at 1800 mug L-1 (86.0%, 90.0% and 86.7% respectively). At 200 mug L-1 none of the androgens altered sex ratio. At 600 mug L-1, only MDHT slightly, but significantly skewed the sex ratio towards males (73.0%). In experiment 2, a single immersion treatment at 14 DPH (1800 mug L-1) significantly increased the proportion of males, but at this time the response was significantly hormone dependent (MDHT, 100.0%; MT, 91.6%; ET, 76.9%). When compared with a single immersion, two-immersion treatments significantly increased the proportion of males in the MT-treated group (from 91.6% to 98.3%), decreased the proportion of males in the MDHT group (from 100.0% to 93.4%) and had no significant effect the ET-treated group (change from 76.9% to 82.5%). The overall comparison of the sex ratio among same treatments from different experiments (a single immersion in 1800 mug L-1) was not significantly different.