[Sexual size dimorphism and female individual fecundity of Saurogobio dabryi in the lower reaches of the Jialing River, Southwest China.]

To investigate the sexual morphological differences and female individual fecundity of Saurogobio dabryi, the sexual size dimorphism, sex ratio and female individual fecundity of 76 individuals collected from the lower reaches of the Jialing River (Hechuan section) in breeding season were analyzed. The results showed that the sex ratio of S. dabryi in the downstream of Jialing River was 1:1 in the breeding season, and no significant difference in the body size between males and females. However, some local morphological traits (such as cephalosome and the truck) exhibited significant difference between males and females, for example, the head, the pectoral fin and the pelvic fin were significantly larger in males than in females, while the width, height and length of trunk exhibited the opposite results, all which were related to the sexual selection. A principal component analysis showed that the first three components accounted for 75.2% of variations in the morphological variables. However, all traits overlapped between males and females, thus they could not be separated by morphological characters. By establishing discrimination function, 92.1% samples could be distinguished. The individual fecundity of S. dabryi ranged from 979 to 19979 eggs, and exhibited significant positive relationship with body length and carcass mass. Compared with the historical data, the fecundities of S. dabryi increased significantly in the present study, which should be the active adaption of the species to the currently depleting population, as well as to the changing of water ecological environment.