Evaluation of common S-type rotifer as an initial food for the larvae of blacktip grouper, Epinephelus fasciatus

摘要

The use of common S-type rotifer (excepting Thai strain, the smaller type), Brachionus rotundiformis, as an initial food for blacktip grouper larvae was investigated at 26 and 22 deg C. Egg diameter, total length and upper jaw length of larvae hatched and reared at 26 deg C were smaller than those at 22 deg C (P < 0.01), indicating 22 deg C give better growth performance. Survival rate of larvae for the entire experiment period was 31.6% at 26 deg C and 42.0% at 22 deg C. Feeding incidence was 100% throughout the experimental period and the number of rotifers found in the larvae's digestive canal gradually increased with the growth of larvae. The mouth of larvae opened at the second day from hatching at 26 deg C and at the third day at 22 deg C. The lorica length of the rotifer ranged from 70 to 230 #mu#m (average 180 #mu#m), and they were fed immediately after mouth opening of the fish. At both temperatures, smaller individuals ,of the rotifer were eaten selectively for three days after mouth opening. Thus for feeding larvae of blacktip grouper, rotifers of high density and small size are recommended.