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 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(a)KM and DJ(b)KM); S-75, J(a75) and J(b75): 75% of FM protein replaced by SBM, DJ(a)KM and DJ(b)KM. White blood cells count, mean cell volume and mean cell hemoglobin 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 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 other groups, optimum inclusion level of J(b) is 50% replacement of FM protein. (C) 2010 Elsevier Ltd. All rights reserved.