Studies On Early Growth And Development Of Digestive System In Spotted Knifejaw(Oplegnathus Punctatus)

The spotted knifejaw,Oplegnathus punctatus, is a widespread subtropical speices in East Asia, with economically very important value in aquaculture. In this study, the histogenesis of digestive system, morphology of embryonic and larval stages, as well as the allometric growth in spotted knifejaw were researched. The results as following:1. Using 32 h, the fertilized eggs of spotted knifejaw finished the hatching at the temperature of(22±1)℃ with the salinity of 29±0.5. By unequal cleavage, the zygotes enter blastula stage at 3hpf, gastrul stage at 5hpf, embryonic shield appeared at 50%-epiboly stage, neural rod and somite were formed at 90%-epiboly stage, Kupffer’s vesicle appeared after the close of blastopore, and the heart begun to beat after Kupffer’s vesicle disappeared, the zygotes finished hatching at 32 h.2. The postembryonic development of spotted knifejaw can be divided into three stages: ① larve fish(0~16dph); ② juvenile fish(17~39dph); ③ young fish(40dph~). The total length of newly hatched larvae were 3.49±0.12 mm, the long diameter of yolk were 0.85±0.12 mm, the short diameter were 0.37±0.03 mm, and the diameter of oil ball were 0.22 mm. At 3dph, the yolk sac disappeared, and the larvae start to ingestion; at 11 dph, the tail-bone began to uptrend; 16 dph, the membrane disappeared and the fin rays of larvae were same as that of adult fish; 22 dph, pigments began to deposite; 30 dph, squamation appeared; 32 dph, lateral lines appeared on the body sides; 39 dph, the scales finished development and the fry entered into young fish stage.3. The ontogeny of digestive system of spotted knifejaw was investigated by histological observation. The results as following: there was no complicateddigestive system in the newly hatching larva, but just a primordial tube composed of simple columnar cells. At 3dph of initial feeding stage, the digestive system differentiated into buccopharynx, esophagus, stomach, intestines(anterior, middle, posterior) and also the hepatopancreas primordium primarily. From 3dph, the acidophilic granules and vascular structure appeared in digestive tube, with the occurrence of pinocytosis ingestion; the pancreas were developed into the outer and the inner secretive parts with large amounts of zymogen particles. At 5dph, the liver cells were transformed into vacuolated state which can absorb fat, with cytoplasm and nucleus were found in the edge. At 17 dph, the gastric glands were found in the stomach wall. As the development of the larval fish, the goblet cells were increasing in the digestive tract with the completing functions. Around 30 dph, the digestive system completed development.4. The total length and body weight of spotted knifejaw larva(0-70dph) were analyzed. The results showed that both total length and body weight displayed the function model of Cubic, with the growth curve of S-curve. The growth of spotted knifejaw can be devided into three different stages with specific growth rate respectively.5. The relationships between growth parameters of functional organs(head length, eye diameter, rostrum length, mouth width, trunk height, tail fin length) and total length of spotted knifejaw were analyzed, which showed the allometric growth patterns of each organs with featured inflection points. By allometry, those functional organs could finish development within the shortest time, which were very critical to larval survival.