Effects of different temperature and delayed initial feeding on larval feeding, early survival, and the growth of coral trout grouper, Plectropomus leopardus larvae

This study investigated the effects of different temperature and delayed initial feeding on larval feeding, early survival, and the growth of coral trout grouper Plectropomus leopardus larvae in relation to endogenous nutrition. Two experiments were conducted: Experiment 1 was conducted to examine the process of yolk and oil globule absorption in the larvae during endogenous nutrition stages at three different temperatures of 26, 28, and 30 deg C. There was no significant difference among each temperature in larval growth. However, larval retaining of oil globule had a tendency of it to be consumed more rapidly with increasing temperature. Oil globule was almost completely consumed when the larval mouth opened in all groups. Experiment 2 was carried out to investigate the effect of delayed initial feeding on the larval feeding, subsequent growth and survival at five different feeding regimes at 28 deg C. The experiment started from larval onset of feeding on 13 hours after mouth opening at 7: 00. The larvae were fed a small S-type of Thai strain rotifers Brachionus rotundiformis at a density of 20 ind./ml to each experimental tank except for No. 5 as follows; No. 1: rotifers were fed initially at 0 hours after onset of feeding (HAOF), No. 2: rotifers were fed initially from 3 HAOF, No. 3: rotifers were fed initially from 6 HAOF, No. 4: rotifers were fed initially from 9 HAOF, and No. 5: no rotifer was fed (starved control). The larvae were examined the feeding incidence, gut contents, and growth at each three hours interval between 0 HAOF and 15 HAOF, subsequently examined at each six hours interval until the end of the experiment. The growth at 45 HAOF of No. 1 and 2 were shown to be significantly faster than those of No. 3 and 4 (P 0.01) , and the growth of larvae of No. 3 and 4 were shown stagnant and/or negative. Feeding amounts of No. 1 and 2 were significantly more than those of No. 3 and 4 during experimental periods. Larval survival rate showed a tendency to be lower value when they delayed onset feeding. In contrast larval growth of No. 5 was terminated at 6 HAOF, subsequently they showed negative growth until the end of the experiment. This terminated time corresponded to 66 hours after hatching (HAH) in No. 5 related with the time at which the larvae completely consumed an oil globule on 64 HAH at 28 deg C based on Experiment 1. These results indicate that early mass mortality of the species occurs due to food deprivation between onset of feeding and 6 HAOF. Their growth and survival will be affected if they fail to feed initially within 6 HAOF at 28 deg C. The present species possessed very weak resistance for starvation.