Sexual dimorphism and its relationship with swimming performance in Tanichthys albonubes under laboratory conditions.

Abstract

To explore the sexual dimorphism of Tanichthys albonubes and its relationship with swimming performances, the morphological characteristics of fins and trunks of male and female T. albonubes were measured and analyzed by using multivariate statistical analysis methods, aiming to explore the difference and its mechanism of swimming performance between male and female under different selected pressure in long-term evolution period and then, providing meaningful information for the protection of T. albonubes. The results showed that body lengths, head depths and breadths, caudal fin areas, distances of snout tip to occipital bone terminus and ventral fin origin to dorsal fin terminus had no significant difference between male and female T. albonubes. The females had significantly higher values in head depths, body breadths, distances of ventral fin origin to dorsal fin origin, snout tip to dorsal fin and to anal fin origin, occipital bone terminus to dorsal fin origin than those in the males. However, head lengths, pectoral fin, dorsal fin, ventral fin and anal fin areas were significantly lower in the females. The results of principal component analysis showed that the contribution rate of the first principal component (PC1) was 74.2%. Obviously loading factors were body lengths, depths and breadths, head lengths, breadths and depths and the distances of each fin mainly reflecting body overall characteristic parameters of T. albonubes. For the second principal component (PC2), the contribution rate was 15.7% and the obviously loading factors were pectoral fin, dorsal fin, ventral fin and anal fin areas which mainly reflected the characteristic parameters of fins. The gender identification of T. albonubes was indistinguishable on PC1, but could be obviously distinguished from PC2. Accuracy rates of sexual discriminant equation which was established by pectoral fin, dorsal fin, ventral fin and anal fin areas and body breadths were 91.8%-92.5%. The results of swimming performance showed that burst swimming speeds (Uburst) had no significant difference between male and female T. albonubes. However, the critical swimming speeds (Ucrit) were significantly decreased in the females than in the males. The findings indicated that the sexual dimorphism of T. albonubes was mainly concentrated on fin characteristics associating with swimming performance. Also having lower Ucrit due to its lower pectoral fins areas than the male, the female T. albonubes had longer hindquarters cadres to ensure high Uburst which facilitated them to avoid predators and other emergency events in volatile streams. Larger fin areas than in the female caused higher Ucirt in the male contributing to chasing female in breeding period and other persistent exercises.