Comparative study of female Chinese mitten crabs based on their sizes and weights.

The Chinese mitten crab (Eriocheir sinensis) is an important aquaculture species in China. While the price of a large crab will generally be 2-5 times higher than that of smaller crabs, it remains unknown whether nutritional quality is affected by market price. To investigate the effect of size on nutritional composition, adult female crabs were collected and assigned to grades I-IV according to decreasing size. The results showed that meat yield and conditional factors were significantly (P < 0.05) reduced with the decreasing size. The different sizes did not significantly (P > 0.05) affect levels of moisture, crude protein (except for hepatopancreatic crude protein), and total lipid. Grade III crabs had the largest hepatopancreatic crude protein level, which was significantly (P < 0.05) increased compared with grade I crabs. A balanced amino acid composition was found in grade IV crabs, while crabs from grades II and IV had the highest essential amino acids score. Levels of highly unsaturated fatty acids, including C22:6n3, and the ratios of n-3 polyunsaturated fatty acids (PUFA)/n-6 PUFA and C22:6n3 (DHA)/C20:5n3 (EPA) in the hepatopancreas were significantly (P < 0.05) increased in grade III crabs compared with the other grades. In conclusion, among the four grades smaller female crabs (average weight: 93-112 g, grades III-IV) displayed an optimal nutritional quality.