Toxicity of the pyrethroid pesticide fenvalerate to freshwater catfish clarias gariepinus: Lethality, biochemical effects and role of dietary ascorbic acid

摘要

Static bioassays were made in the laboratory to determine lethal concentration of the pyrethroid pesticide fenvalerate [(RS)-alpha-cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)-3-methylbutyrate] for the freshwater catfish Clarias gariepinus and effects of sub-lethal concentrations of the pesticide on some biochemical parameters of the fish. For exposure periods of 24 to 96 h, LC_(50) values of fenvalerate ranged from 5.83-4.76 μg/L and 4.24-2.94 μg/L, respectively for water and acetone soluble fenvalerate. Two sublethal concentrations of fenvalerate were used in the bioassays for biochemical parameters: 2.1 μg/L for 24 h and 1.4 μg/L for 96 h exposure, both concentrations representing 50% of LC_(50) value of acetone soluble fenvalerate for the respective exposure period. Hepatosomatic index, liver glycogen, alkaline phosphatase of liver and ascorbic acid of blood, liver, and kidney decreased while haemoglobin (Hb) %, plasma glucose levels and acid phosphatase level of liver increased after 24 h exposure to 2.1 μg/L fenvalerate. Longer exposure (96 h) to even a lower concentration (1.4 μg/L) of fenvalerate resulted in reduction of all the parameters (except Hb %) tested as compared with control. Fish previously fed for 60 days with a diet supplemented by a high level of ascorbic acid (100 mg/100 g diet) could reverse most of the effects caused by 24 h exposure to 2.1 μg/L fenvalerate. A lower level of ascorbic acid (50 mg/ 100 g diet) supplement could not influence these effects of fenvalerate. Even the higher dose of ascorbic acid supplementation (100 mg/100 g diet) could not relieve the stress parameters, except for Hb% and HSI, when the pesticide was applied at 1.4 μg/L for a longer time period (96 h).