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Abstract
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Nitrogen compounds are considered as one of the most important environmental pollutants among which ammonia is the most dangerous and significant one. In the present research, the effect of different ammonia concentrations on Vannamei post larvae with the mean weight 0.3 ± 0.05g and mean length 0.67 ± 3 cm was investigated in 2015. The post-larvae were exposed to ammonia concentrations of 0, 6, 13, and 19 mg/l in 6 treatment groups and 2 control groups with three replicates and they were tested using semi-static method at two salinities of 10 ppt. (control 1, treatments 1, 2, and 3) and 20 ppt. (control 2, treatments 4, 5, and 6), pH=8.2, temperature of 30.66?C during a 45-day period. Initially, the LC50 value of ammonia in a period of 48 hours at two salinities of 20 ppt and 10 ppt (63/13 ppm) were calculated. Then, the effect of different ammonia concentrations on some growth and molting parameters of post-larvae were studied. The results were statistically analyzed using SPSS software. The lowest degrees of growth factors were observed at 19 mg/l ammonia concentration at 10 ppt. salinity. Post-larvae grown at these concentrations showed lower growth rate and a relatively lower food absorption. The highest increase in weight and length, and the maximum weight gain were observed in the treatments of control groups which were significantly different from other treatments. The highest mortality rate was also reported for 19 mg/L ammonia concentration at 10 ppt salinity that was calculated as 69.44 ± 31.54%. According to the results of this study and the Tuky test with confidence level of 95%, it was found that, in general, the values of growth factors in the shrimps exposed to 19 mg/l ammonia concentration were lower than those of the control group and the ammonia concentration of 6 mg/l (p? 0.05). Also, the results indicated that ammonia increases molting frequencies in the experimental post-larvae. The general inter-molt period for post larvae in a 45-day period ex
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