Protein rich Jatropha curcas kernel meal is toxic. It was detoxified using heat treatment and solvent extraction. Two duration of detoxification process were investigated: shorter (30 min) and longer (60 min) and the detoxified meals so obtained were designated as J a and J b respectively. Common carp fingerlings (252 fish; 3.2 ± 0.07 g) were fed with the following diets: Control containing fishmeal (FM); S 50, J a50 and J b50: 50% of FM protein replaced by soybean meal (SBM), detoxified Jatropha kernel meal (DJ aKM and DJ bKM); S 75, J a75 and J b75: 75% of FM protein replaced by SBM, DJ aKM and DJ bKM. White blood cells count, mean cell volume and mean cell haemoglobin concentration, calcium and sodium ions and total bilirubin in blood did not differ significantly among the groups. Higher ( P > 0.05) RBC count was observed in plant protein fed groups compared to control group. Highest alkaline phosphatase and alanine transaminase activities in blood were observed in J a75, which were not different ( P > 0.05) from those in J a50 group, but were higher than in the other groups. No adverse histopathological changes in liver and muscle of any group were observed, but intestinal mucosa of J a75 groups showed severe pathological lesions. The results demonstrate that Jb was completely detoxified. Since the performance of J b50 group was similar to control group and better than the other groups, optimum inclusion level of J b is 50% replacement of FM protein.