The Study On Histology And Biochemical Composition In Polyploidy Pacific Oyster (Crassostrea Gigas)

For determining the energy resource, energy mobilization of reproduction, and the relationship of reproduction and glycogen metabolism, biochemical composition during a annual period, glycogen phosphorylase and glycogen synthetase during sexual maturation were compared in diploid and triploid Pacific oyster (Crassostrea gigas), and cell size of several organs, ultrastructure and surface structure of the gill in diploid and triploid Pacific oyster, ultrastructure of spermatozoa in diploid and tetraploid Pacific oyster was also compared with histology method in this study to examining the mechanism of fast-growing in polyploidy. The result showed that:1 Gill epithelium nucleus major-axis size, hemolymph nucleus diameter in the connective tissue of mantle and labial palps were significantly (P0.001) larger in triploids than in diploids, no significantly differences were found in rectum epithelium height between diploids and triploids. The results support the hypothesis of Polyploid gigantism and show the effect of polyploidy on nuclear size. The ultrastructure of gill filament show significant difference in the mucus cells of diploid and triploid oyster, and the surface structure of the gill of diploid and triploid oyster show that filament width and inter-filament distance are larger in triploids than in diploids, the minuteness structure of filament are more delicate in triploids than in diploids, and the dimension of holes which formed by connection of inter-filament are greater in triploids than in diploids. That indicates there might be differences in respiring and feeding between diploid and triploid Pacific oysters.2 The ultrastructure of spermatozoa in diploid and tetraploid showed that ultrastructure of tetraploid oyster was similar to diploids. The mean size of acrosomes (1.02 0.06m vs. 0.88 ?0.08m), nuclear (1.93 0.08m vs. 1.87 0.11m) were larger than that from diploids, and number of mitochondria were more than diploids (5 or more than 5 to only 4 in diploid); moreover, these mitochondria were not in one layer in tetraploids. The increased number of mitochondria in tetraploids seemed to adapt the demanding of more energy for fecundation in tetraploids because of larger size.3 Biochemical compositions in gonad and adductor muscle between diploids and triploids in the Pacific oyster, Crassostrea gigas, during an annual period wereexamined. The results indicate that biochemical composition in oysters is closely related to its sexual maturation. As sexual maturity progressed, the glycogen content of gonad in diploids decreased (decreased by 78.57%, P<0.01), and maintained low level during spawning, then increasing, in winter (October to February of next year) glycogen content keep higher level than that of spawning. However, protein and triglyceride content increased with gametogenesis (increased 110.8% and 104.5%, respectively) and decreased in spawning. Glycogen levels of gonad in triploids also declined, but at a slower rate, and after spawning glycogen content of triploid maintained in a high level (21.7%~29.2%), protein and triglyceride content in gonad showed similar p attern of utilization as diploid. The results from above suggested that glycogen was the major energy resource for reproduction, triploid showed a different pattern of glycogen utilization. Glycogen content of adductor muscle in diploid and triploid oysters both decreased during reproductive period, but in triploid decreased slightly (67.9% in diploids vs. 37.2% in triploids), then increased after spawning in both diploids and triploids, in winter glycogen content of adductor muscle maintained lower level. Protein and triglyceride content in adductor muscle increased during gametogenesis, and then deceased in spawning. The results from adductor muscle suggesting adductor muscle is an important organ for energy storage and mobilization, and during gametogenesis, glycogen break down in adductor muscle provided energy for gonad maturity, protein and triglycerides also break down to provided energy during spawning.4 Seasonal ch...