حمیدرضا نوریزدان

The present research was conducted in 2015, aiming at investigating the effect of ammonia on the growth and molting of western white leg shrimps (Litopenaeus vannamei) at two salinity levels of 35 ppt. and 45 ppt. with mean weight 0.3 ± 0.05 g, mean length 3 ± 0.21cm at 30? C and pH=7.88 for 45 days. Results of this study indicated that increase of ammonia concentration to 6 mg/l did not have any significant effect on weight gain (WG), body weight gain (% BWG), special growth rate (SGR), daily growth rate (DGR), condition factor (CF), feed conversion rate (FCR) and survival rate (SR) (p> 0.05). But ammonia concentrations higher than 6 mg/l (13 and 19 mg/l) had a negative effect on the growth of post larvae, and their growth significantly reduced at these concentrations. The lowest value for the mentioned parameters was observed at 19 mg/l ammonia concentration and 35 ppt salinity and those post larvae grown at these concentrations displayed a slower growth and a relatively lower food absorption. The highest mortality rate was also observed at 19 mg/l ammonia concentration and at 35 ppt salinity which was calculated as 80.55 ± 4.80%. According to the Tukey test with confidence level of 95%, it was found that there were significant differences among the different treatments in terms of increase, weight gain rate, special growth rate, daily growth rate, condition factor, feed conversion rate, and survival rate (p< 0.05) and the best values for these factors were observed in the control group at 35 ppt. Also, the results demonstrated that ammonia increases the molting frequency in the experimental post larvae. The general inter-molt period for post larvae in 45 days at concentrations of 0, 6, 13, and 19 were calculated as 11.55 ±0.69,10.77 ±1.26, 9.44 ±1.01, and 8.66 ±0.57 days under 35 ppt, and 11.10 ± 0.50, 10.66 ± 0.57, 10.10 ±0.50, and 9.55 ± 0.19 days for PLs reared under 45 ppt salinity. According to the results obtained in this research, it can be argued that as