SOMATIC AND LAPILLUS OTOLITH ONTOGENETIC GROWTH AND DEVELOPMENT IN LARVAL AND JUVENILE ELOPICHTHYS BAMBUSA RICHARDSON IN THE XIANG RIVER

Elopichthys bambusa Richardson is a piscivorous fish distributes widely in the east floodplain waters, China. This fish is a potamodromous species, which grows and matures in the floodplain lakes and then naturally migrates into the attached rivers for spawning. E. bambusa used to be a very important commercial species, however, resource of this fish has been dramatically destroyed in most waters due to overfishing and habitat degradations. With the success of artificial breeding of E. bambusa in early 2000s, this species becomes an important aquacultural species and also a target species of stock enhancement typically in some reservoirs in the middle and lower reaches of the Yangtze River. Mortality rate of fish during early life stage is high for both wild populations and artificial seeding production. An understanding of early growth and development is essential not only for wild population conservation, but also for artificial seeding production. In this study, a total number of 370 larval and juvenile E. bambusa was collected in the Xiang River from June to July, 2008. Otolith analysis revealed that age of the specimens ranged from 4-25 days, and the back-calculated hatching dates were during May 27th to June 22nd. The mid-age of stage transition from preflexion to flexion was at the 6th day; from flexion to postflexion was at the 10th day; from postflexion to juvenile was at the 15.5th day. Piecewise regression revealed a knot in the growth functions of either body length or otolith radius, were both at the early postflexion stage (the 12nd-13rd day): the growth rate after the knot was 5 times and twice of that before the knot for body length and otolith radius respectively. The shape of lapillus was round in the preflexion stage; in the flexion stage, the anterior- posterior axis growth significantly exceeded along the dorsal-ventral axis, and the shape became oval; the otolith further elongated in the postflexion stage, and the peak of the posterior emerged to shape the whole lapillus pear; in the juvenile stage, the peak smoothed and the shape was mussel. Otolith shape and microstructural analyses can provide essential information revealing the critical events in the early life history of E. bambusa.