Early Development And Related Enzymatic Activity In Rock Bream

The rock bream, Oplegnathus fasciatus, a subtropical and carnivorous species, is an economically important marine fish in East Asia. The high commercial and ornamental value makes it a promising aquaculture species in the future. However, to some extent, the lack of information on ontogenetic development has restricted the breeding industry of this species. In this study, the allometric growth, histogenesis and enzymatic activity in rock bream were analyzed. The results are as follows:1. At the general condition for fingerling-production, the total length and body weight of rock bream larvae were measured from hatching to 50 day after hatching. The increase of total length and body weight could be estimated with the Cubic function and took on the S-Curve. The curve could be divided into three phases and each phase possessed different growth rate.2. The head length, head height, trunk height, eye diameter, mouth width, abdomen length, tail fin length and rostrum length of rock bream were measured and the relationship between them and the total length was analyzed. The result showed the allometric growth in rock bream larvae. By analyzing the inflexion points in growth curves, in combination with morphological development of the larvae, we found that some important organs (head, mouth, eye, digestive tract and fins) had developed prior to other ones. When rearing rock bream larvae, the best environmental condition should be established by making the important organs prior development.3. The embryonic development of rock bream was studied from fertilization until hatching (HE & Mallory). The hatching occurred approximately at 25 h after fertilization at 23.5±0.5°C. The embryogenesis is divided into seven stages: Zygote period, Cleavage period, Morula period, Blastula period, Gastrula period, Segmentation period and Hatching period. The first cleavage furrow of rock bream fertilized eggs is vertically oriented, as is usual until horizontal cleavage occurs at the fifth cleavage. The blastocoel is observed between the blastoderm and I-YSL at blastula period. At 90%-epiboly stage, the earliest somitic furrow appears in the middle of embryo. The Kupffer's vesicle consisting of ventrally I-YSL and dorsally columnar cells appears with the completion of epiboly. It degenerates gradually with the penetration of some eosinophilic granules and disappears completely at 20 h 30 min after fertilization. The digestive tract, a straight tubule, is differentiated into foregut, midgut and hindgut. The staging series provides a preliminary baseline reference for future studies on embryos of the rock bream.4. The ontogeny of rock bream larvae was investigated by histological observation from hatching to 50 days after hatching (HE & mercury-bromophenol blue). The histogenesis of main organs (eyes, gill, brain, heart, digestive system, immune system and swim bladder) was described in detail. Overall, rock bream presented a similar pattern of histophysiological ontogeny of organs compared with other marine teleosts. The main interspecific variability encountered resides in the timing of organ development.5. The activity of pepsin, alkaline phosphatase, Na~+ K~+-ATPase and Superoxide Dismutase (SOD) were assayed using test kits. Trypsin activity was measured using Nα-benzoyl-DL-arginine-p-nitroanilide (BAPNA) as substrate. Protein was determined by the Bradford method. The activities of the different enzymes assayed were expressed in relation to soluble protein in the extracts (specific activity). The analysis of enzymatic activity, in combination with the observation of organogenesis, can better illuminate the early development of rock bream.