Study On Biology Of Epinephelus Coioides During Early Developmental Stage

In this dissertation, the biology of Epinephelus coioides during early developmental stage were focused, the mainly areas are follows: feeding habits and growth of larval and juvenile E. coioides; study on early development of E. coioides; effects of temperature and salinity on growth and survival of young E. coioides. The major obtained results were as follows:The morphological characteristics of early development of E. coioides were observed and described during October and December 2005 and in April 2006. The post embryonic development of E. coioides was divided into larval stage, juvenile stage as well as young fish stage, based on the features of the yolk-sac, finfold , scale, second dorsal fin spine and pelvic fin spine. The average total length of newly hatched larva was 1.68mm(1.60~1.78mm). At the water temperature of 21.0~28.5℃and the salinity of 24.8~28.3, the embryonic development took 5 days to develop into prelarvae, and then took another 26 days to develop into postlarvae. The mouth could be seen three days after hatching. The juvenile stage developed from 32 to 68 days after hatching. After 69 days, the fish developed into the early young fish period. The growth and configuration of the second spine of dorsal fin and the first spine of ventral fin is most obvious changes during early development of E. coioides. In addition, the similarities and differences of morphological characteristics of larval, juvenile and young fish between 4 species of Epinephelus as well as the crises that appeared during the growth and development of larval, juvenile and young E. coioides were discussed.The feeding behavior and the growth of larval and juvenile E. coioides was studied in October and December 2005. It shows that the larvae began to feed on the fourth day after hatching at water temperature of 26.5~28.5℃. The initial diet can be fertilized eggs and trochophore of oyster and than rotifer, Artemia nauplii, copepod and fish meat, in consequent during the growth. Based upon the observation of 422 individuals, it was found that the feeding rate reached 95.1% with intestinal fullness fluctuated between 0.96%~34.15% and the diel feeding amount was 45.83%~82.08% of the body weight. Rhythm of feeding intensity was obvious during the day and night. Higher feeding intensity was found at 11:00 a.m. and 15:00 p.m. for the larvae and was at 13:00 p.m. and 17:00 p.m. for the juveniles. Little feeding activities were observed during the night. When mixed food is used, larval and juvenile fish preferred food particles of large size. The time for feeding from empty stomach to fullness, the average amount of food in full stomach, and the time for food digesting by larval and juvenile of E. coioides were measured. The correlations for feeding amount and body weight is expressed as y = 0.017W + 0.198, for total length and day age is LT = 2.229e0.038D, for body weight and day age, W = 0.063e0.130D, and for total length and body weight, W = 0.0047LT3.319.The observations on the effects of temperature and salinity on growth and survial rate of young E. coioides were studied. It showed that the young could grow and survive at temperature 15~32℃, and the optimum at 22~28℃. Under suddenly changing temperature conditions, the survival rate of the young was more than 92.5% in 48 hours at temperature 14~32℃, the survival rate was 100% at temperature 17~29℃. Under gradually decling temperature conditions, the survival rate of the young was 80%~95% at temperature 12~32℃. The suitable salinity is 9~39. Under suddenly changing salinity conditions, the survival rate of the young was more than 95% in 48 hours at salinity 4~39. And the young couldn't survive in fresh water. Under gradually decling salinity conditions, the survival rate of the young was 91%~100% at salinity 4~39, and the survival rate was more than 98% at salinity 14~39.