Quality grading and nutrition value determination of fish are. nowadays necessary for aquatic processing. The present study was conducted to investigate a new, applied and cheap method of fillet quality grading for common carp (Cyprinus carpio) using fish size, based on mathematical equations. For this reason, 61 specimens of cultured market size carp were used and after filleting, their moisture, lipid, protein, energy and ash content were measured. Then, the relationships between proximate composition components of fillet and fillet length were studied. Results showed that there is an inverse linear regression relationship between logarithm of moisture content and logarithm of fish length (P<0.05). The results also showed that there is a positive linear regression relationship between logarithm of lipid and energy content and logarithm of fish length (P<0.05). No significant relationship was found between logarithm of fillet protein and ash content and logarithm of fish length (P>0.05). Regarding

the relationship between proximate composition of cultured carp fillets and fillet length machine fish sorting based on fish length and grading of moisture, lipid and energy content is feasible. We also found it feasible to determine type of processing and proximate composition of the prepared common carp.