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The study was designed to arrive at an experimentally-determined application factor for fixing tentative water quality criteria for phenol in tropical freshwaters. Larval rohu Labeo rohita (14-18 mm total length, 118-139 mg wet weight) were subjected to static lethal bioassay. The 24-h LC50 value was found to be 32 mg·L· 1 at 29±1 °C. Juvenile rohu (26-33 mm total length, 226-273 mg wet weight) were exposed to sublethal phenol concentrations (0.1, 0.5, 2, 5 and 10 mg•L·1) for 28 d at 29±1°C without aeration. Treatment media were replaced every 48 h. Fish were fed a pelleted diet at 6% wet body weight per day. Rohu exposed to 5 and 10 mg•l·1 phenol showed significantly lower mean wet weight gain, specific growth rate, food conversion efficiency, and dry matter and protein digestibility. These fish also had higher moisture content, and lower protein, lipid and ash contents, as body nutrients were depleted. Juveniles exposed to the lower phenol concentrations of 0.1, 0.5 and 2 mg·l·1 were not significantly different from the control. The maximum allowable toxicant concentration for juvenile rohu was 3.16 mg·I-1, indicating an application factor of 0.10.

The survival and .growth of Chanda (= Ambassisy gynmocephalus (Lac.] fry (8·g ± 0'2mm) collected from Murukumpuzha Lake (9·34%0) for a ninety day period in different salinity grades were studied. A faster rate of growth is exhibited by the fish in the highest salinity grades(22'41 and 28· 51%0)' even though during the first month, growth and health was apparently better in the lower salinity grades (4'11, 10·21 and 16'31%0)' Assimilation efficiency also showed a similar gross picture. Thus in C. gymnocephalusvtu: euryhaline species, the fry show preferred salinity gradients for optimum growth within the fluctuating salinity regime at a stable temperature (26 ± 2°C) and hence may make salinity bound emigrations with growth.