Comparison of the body proximate compositions of juvenile bronze gudgeon (Coreius heterodon) and largemouth bronze gudgeon (C. guichenoti) in the upstream region of the Yangtze River

The body proximate compositions were assessed in juvenile Coreius heterodon and C. guichenoti from the upstream of the Yangtze River. The migratory C. guichenoti has a higher lipid content (FAT) than the residential C. heterodon. FAT of C. guichenoti showed an interesting pattern of increase, where FAT increased up rapidly and then leveled off as body mass (M) increased above 6.5 g, suggesting that the lipid concentration reaches an upper limit of deposition. In both species, FAT of the smaller individuals was lower than protein content (PRO), but FAT increased more rapidly than PRO as the fish grew. This indicates that more energy was allocated to protein synthesis than lipid in the smaller fish, with an energy allocation shift from protein synthesis to lipid storage as the fish grew. Strong relationships between both FAT and energy content (E) and water content (WAT) were found in both species, suggesting strong predictive power for future application. However, different models for the two species should be used to predict FAT or E by WAT.