Growth rates, relative growth and a potential aging method using vertebral centra in Silurus biwaensis(Siluriformes: Siluridae)

Relative growth and relationship between age and growth in Silurus biwaensis were examined on the basis of the body size data of the catfish collected from Lake Biwa and the reared catfish which were hatched from artificially inseminated eggs. Although it had been reported that the proportion of head length to body length increased with growth in S. biwaensis, such a relationship was not found for 218 catfish that were examined in this study. On the other hand, the proportion of head length to head width significantly decreased with SL in females. This result indicated that the narrow head shape peculiar to S. biwaensis becomes slightly squarer in bigger females. The three catfish reared from the hatching grew to 196-410mm SL for 2.7 years (73-152mm/yr). This growth rate was in contrast with that of a tagged adult male, which grew only 50mm from 460mm SL to 510mm SL in the lake for two years (25mm/yr). These results suggested that the growth of the adults might extremely slow down after the fast growth at the immature stage. This study also reported that the number of transparent zones in vertebral centra of S. biwaensis increased with growth. The vertebral centrum may possibly be utilized as an age indicator for this species and the other kinds of Silurid