This research deals with the study of histo-pathological changes induced in the gallbladder of the fish Catla catla, due to lindane, a persistent environmental contaminant intoxication. For present work healthy specimens of the fish Catla catla were collected from the nearby river Narmada and acclimatized at laboratory conditions for 10 days and then treated with 1.2% of lindane for 30 days. Histological preparations were made by sacrificing controlled fish and 30 days treated fishes. Fishes were dissected and organs were removed and fixed in alcoholic bouins solution for 24 hours and proper microtomy technique was employed. Eosine and hematoxylene were used for cellular differentiation. These studies show many histopathological changes in gallbladder of the fish. Crystallization of bile and deformities in the normal structures of epithelial lining and muscular layer are the main toxic effects significantly noticed in this organ.

The effects of feeding Nile tilapia with Azolla, an atmospheric nitrogen fixing fern, on water quality and sediments characteristics was evaluated in 90 days pond experiment. Fish were fed with six diets differing by their level in the Azolla meal (AM), as partial fishmeal (FM) substitutes: 0%, 10%, 20%, 30%, 40% and 50%. The Azolla-free diet (0%) served as a control. Growth performances were higher in fish fed the control diet and a significant decreasing trend was obtained in fish fed diets containing more than 20% of AM (P<0.05). Significant higher concentration in soluble reactive phosphate (SRP)( 0.14-0.38mg l-1) and total phosphorus (TP) (0.63-1.22mg l-1) were found in water of ponds with 0 and 10% AM (P<0.05). P content of soil matter (0.01-0.02%) was identical in all ponds (P>0.05). Values of nitrogen compounds in water were similar in all experimental ponds. The sediment C/N atomic ratios ranged from 6.7 to 19.6, indicating an influence of allochthonous material in ponds. This C/N ratio which decreased significantly in high AM-ponds (P<0.05) was directly influenced by the AM-nitrogen provided: C/N at.= -0.0057N2+0.0303N+18.238 (R²= 0.79; P<0.001). The present study proved that the fern Azolla could sustain Nile tilapia growth by serving not only as feed ingredient but as a nitrogen providing source in rearing ponds, thus improving water natural productivity, beneficially to phytoplanktonophagous fish in pond aquaculture.