An investigation on possibility of Nile Tilapia (Oreochromis niloticus) feminization under the condition of brackish water in Bafgh

Abstract

This study was aimed to investigate the effect of different doses of oral diethylstilbestrol (DES) on feminization of Nile tilapia (Oreochromis niloticus) larvae under the condition of brackish water in Bafgh fisheries research center. This Experiment was comprised of two control groups in two replicates and two experimental ones in three replicates. At the beginning of the trial, a number of 2150 larvae were randomly distributed among 10 replicates that were under treatment for 45 days. The diets in two control groups, i.e. non-treated, C1, and ethanol treated feed, C2, and the ones in two experimental groups, i.e. 200 and 400 mg DES/k of feed, E1 and E2, were administrated to 7 day post fertilization (dpf) larvae for a period of 35 days and then until day 45, the larvae were fed with ordinary feed. At the end of the trial, the gender ratio of larvae in different groups was determined by squash test in 50 randomly selected individuals from each replicate. The results showed no significant differences for gender ratios within control groups (respective male to female ratio in C1 and C2 was 47:53 and 57:43). However, the corresponding ratios within experimental ones, fed with 200 and 400 mg DES/k of feed respectively, was significantly different (P<0.05). Noteworthy that the percent of females between two experimental groups (E1 and E2) was not significantly different (70.0 and 64.7 respectively) but it was significantly different with ratios in experimental groups (P<0.05). The total body length and live body weight were determined at the begging and then at day 30 and 45, it was randomly measured in 20 larvae from each replicate. At the beginning of the experiment, the mean body weight and total length of larvae was 0.012 gram and 1.03 centimeter respectively. The respective averages at day 30 and 45 were significantly different among groups (P<0.05). Survival rate was significantly different among groups (P<0.05), being highest in E1 and E2 respectively whereas lowest in control ones (56.51 and 58.84 in C1 and C2 respectively).