2016 Volume 80 Issue 2 Pages 129-135
Age, growth, and maturation of elongate ilisha Ilisha elongata were examined in the Seto Inland Sea, Japan, from 2003 to 2005. Standard length (SL) ranged from 250 to 556 mm for adult and immature fish (n=356) and from 52 to 85 mm for juvenile fish (n=33). Almost all of the large-sized fish ≥430 mm SL (97%) were identified as female. The initial maturation sizes of male and female were estimated to be approximately 300 mm and 360 mm, respectively. Seasonal variation in gonadosomatic index and the occurrence of eggs of this species in the same area based on past studies suggest that the spawning period extends from June to August. Clear check marks on sectioned otoliths were formed at the marginal edge once a year between April and October, confirming their annual formation in otoliths. The maximum ages were estimated to be 10 years old in both male and female, but 85% of individuals≥8 years old consisted of females. The von Bertalanffy growth equations based on age–length relationships were estimated, as follows: SLt=422.6 (1-e-0.542 (t+0.166)) for males and SLt=497.1 (1-e-0.414 (t+0.225))) for females, where SLt is the SL (mm) at t (year). These two equations were significantly different (p<0.01), indicating that females become larger than males.
