EARLY STAGE STARVATION ON SURVIVAL AND GROWTH OF THE LARVAL SILVER CARP, HYPOPHTHALMICHTHYS MOLITRIX

Food deprivation after a prolonged downriver drift could severely affect the growth and survival of silver carp Hypophthalmichthys molitrix larvae. In order to study the effect of the first feeding time on feeding ability, survival and growth of silver carp larvae, this study was carried out with a delay of 0 (feeding group), 2d, 4d and 6d in the feeding group and the starvation group at water temperature of (24±1)℃ under experimental conditions, respectively. Silver carp larvae were reared in experimental tanks (25 L) for 30d in five treatments. The feeding time of the five treatments in triplicates was 3 days after hatching (dah), 5dah, 7dah, 9dah and FG (fasted group) respectively. The results were as follows: the initial feeding rate of silver carp larvae was 36.67% at 3dah and reached the point of no return (PNR) at 11dah. The timing of first feeding had a great influence on the survival rate of silver carp larvae. All the larvae in the starvation group died at 15dah, while the survival rate of the larvae in the fed control group was 69.00% at 15dah. With the extension of delayed feeding time, the survival rate of larvae decreased significantly. Larval growth was significantly affected by the time of first exogenous feeding. The total length specific growth rate (SGR_L) and body weight specific growth rate (SGR_W) of silver carp larvae in different treatment groups exhibited a general downward trend during starvation periods. SGR_L of larvae at 14dah and 30dah in feeding group was higher than that in other delayed feeding treatments. Starvation affects the morphological characters of silver carp larvae. Principal component analysis of morphological ratio data showed that the morphological differences between starvation group and feeding group were mainly caused by the differences in head morphology and myotome height. Fed larvae began to show notochord flexion from 8dah, and all of them turned to the notochord flexion at 14dah, whereas unfed larvae remained at the preflexion stage until 14dah. In order to avoid potential mortality by starvation and obtain adequate growth and development, the silver carp larvae must establish successful initial feeding within 2d before and after yolk sac depletion. This study can provide basic data and reference for the exploration of early recruitment process and population recruitment mechanism of silver carp.