Abstract: Muscle content in 1 ～ 2 year-old Catla cat la w as determined .Biochemical composi tio ns of muscle were analysed for the fish of same seasons but dif ferent ages .The water content of muscle decreased g radually , but the contents of protein and fat increased w ith the increase of age .The content s of ash and non-nit rogen ex tract had a lit tle change , while the total content of amino acid had some change with the increase of age .How ever , there w as no regularity among these three co ntents .For the same age f ish , the w ater content of muscle in summer was lower than that of muscle in winter , w hile the contents of pro tein , fat , ash and non-nitrogen ex tract of muscle in summer w ere higher than those of muscle in w inter .The biochemical composi tio n of muscle of 1 year-old Catla cat la and Aristichthys nobi lis w as relatively indentical . For 2 year-old f ish , biochemical composition of muscle of Cat la catla w as hig her than that of A . nobi lis ex cept for the content s of water and ash .The changes in w ater and protein contents and also in w ater and fat content in Cat la catla muscle were of a negative correlat ion .