Effect of chemical herbicides and insecticides on mortality and feeding of silver carp (Hypophthalmichthys molitrix)

Fingerlings of Silver Carp (Hypophthalmichthys molitrix) were used in an ecotoxicological investigation. The fish were exposed to (۰.۳-۱۰ mg/l) Machete, (۳-۵ mg/l) Saturn, (۱.۵-۱۳ mg/l) Diazinon and (۱-۱۰ mg/l) Malathion to measure the toxicity effect of these chemicals on mortality, feeding and ingestion rate. Methods for investigation on mortality were according to TRC (۱۹۸۴) and feeding behavior, according to Gould Equation (۱۹۵۱). Porbit analysis was used for evaluation of obtained data. LC۱۰ of these toxic compounds were ۰.۱۷-۰.۲۳, ۲.۸۵-۳.۷۳, ۰.۶-۰.۹۵, ۰.۸۷-۱.۳۴ mg/l for Machete, Saurn, Diazinon and Malathion respectively. Experiments showed that Machete and Diazinon in comparison with Saturn and Malathion were highly toxic for fingerlings of silver carp. At first fish showed to be disturbed, then moved rapidly and exhausted. A secretion of excess mucus was also noticed and eye-ball became expanded. There was also blanching of the skin. The fish surfaced sometimes on their side and became unbalanced which resulted in death. Abnormal behavior of fish became greater with the increase of pesticides concentration. In these exposures pH was decreased, in contrast with the amount of water hardness. LC۱۰, LC۵۰ and LC۹۰ form ۲۴ to ۹۶ hours were mostly decreased. Feeding experiments showed that ۸ hours exposure below the LC۵۰ values reduced ۵۰ percent of feeding and ingestion rates.