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Ninety-six hours static bioassays were made in the laboratory to determine acute toxicity of cypermethrin to five non-target freshwater organisms belonging to different taxa and niche. Susceptibility of the organisms to cypermethrin was in the order: the crustacean Diaptomus forbesi > the aquatic insect Ranatra filiformis > the freshwater carp Cyprinus carpio > the tadpole larva of the toad Bufo melanostictus > the oligochaet worm Branchiura sowerbyi. Ninety-six hours LC50 values of aqueous cypermethrin ranged from 0.03 microg/L for the crustacean to 9.0 microg/L for the tadpole larva. The value was very high (71.12 microg/L) for the oligochaet worm. LC50 values changed with hours of exposure till 72 h after which cypermethrin became inactive in both aqueous and acetone solution. Acetone solution of cypermethrin was more toxic to B. sowerbyi, C. carpio and the tadpole larva. There was no significant difference in susceptibility of any other test organism between aqueous and acetone solution of cypermethrin.

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A 60-day feeding trial was conducted to test the e¡ect of partial replacement of ¢shmeal by ¢sh-o¡al (FO) in the diet for the freshwater cat¢sh Heteropneustes fossilis. Three isonitrogenous (31.4% CP) diets were formulated to include a reference diet (T1) with 40% ¢shmeal (FM) and 0% FO and two supplementary diets: one (T2) containing 25% FM and 25% FO and another (T3) containing 20% FM and 30% FO. The FO was fermented along with mustard oil cake and rice bran before using it as an ingredient in the preparation of feed. Two separate trials were conducted with these three diets: a growth trial and a digestibility trial. H. fossilis fed the diets containing FO showed better growth and proximate composition of carcass than those fed the reference diet. Fish fed T3 diet showed maximum feed conversion, protein utilization and growth. Apparent protein digestibility (APD) was also signi¢cantly higher in the T3 diet as compared with the T1 diet. The results of the trial indicated that using microbial fermentation, FO could be included up to a 30% level as a partial (50%) replacement of ¢shmeal in the formulation of diet for H. fossilis.

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Lethal concentrations of cypermethrin, dissolved either in water or acetone, were determined for freshwater catfish Heteropneustes fossilis at different hours of exposure by static bioassays. Up to 48 hours, there was no difference between LC(50) values of aqueous and acetone solublized cypermethrin. Seventy-two-hour LC(50) values of aqueous cypermethrin and acetone solublized cypermethrin to H. fossilis were 0.67 and 1.27 microg/L, respectively. Lethal values remained unchanged beyond 72 hours. The fish exposed to even lower concentration of cypermethrin (0.5 microg/L) showed hyperactivity.