Lethal and sublethal toxicity of monocrotophos, an organophosphate pesticide on the juveniles of rohu--Labeo rohita (ham.) under tropical conditions

摘要

The study was designed to arrive at an experimentally-determined application factor for fixing tentative water quality criteria for monocrotophos, an organophosphate pesticide under tropical conditions. Juvenile rohu--Labeo rohita (46.82 +- 0.52 mmtotal length, 1012.29 + 43.12 mg wet weight) were subjected to static lethal and sublethal bioassay, with periodic replenishment of treatment media. The 48 hr LC_(50) value was found to be 104.02 mg/l at 28 +- 2 deg C. Juvenile rohu were exposed to concentrations (2, 5, 10, 15, 20, and 30 mg/l) for 32 days at 28 +- 2 deg C without aeration. Treatment media were replaced every 24 hr. Fish were fed a pelleted diet at 6 percent wet body weight per day. Rohu exposed to 5, 10, 15, 20, and 30 mg/l monocrotophos showed significantly lower mean wet weight gain, specific growth rate (SGR) and food conversion efficiency (FCE). But fishes of the lowest monocrotophos concentration of 2.0 mg/l were not significantly different from the control. The MATC (maximum acceptable toxicant concentration) for juvenile rohu was 3.16 mg/l (2 to 5 mg/l) for SGR and FCE as end points (the most sensitive) and 24.5 mg/l (20 to 30 mg/l) for percentage survival as an end point (the least sensitive) indicating application factors of0.03 and 0.24 (MATC/48 hr LC_(50)) and 0.07 and 0.53 (MATC/96 hr LC_(50)) respectively.