| Based on methods of experimental ecology,the biological characteristics of embryos and juvenile obscure puffer(Takifugu obscurus)under controlled conditions were studied。Na~+-K~+-ATPase(NKA)and the osmolality of the blood were assayed.The effects of salinity on location,number,and ultrastructure of chloride cell were also investigated.The main results are as follows.1.In this study,the Na~+-K~+-ATPase activity and embryonic development of obscure puffer were investigated at salinities of 0,2,4,6,8,9,10,11,and 12 parts per thousand (ppt),respectively.Results showed that after an abrupt transfer to the salinities of 0, 2,4,6,8,9,10 ppt,survival rates of embryos were high throughout the experiment, and there were no significant differences among them(P＞0.05),whereas most embryos died gradually at salinities of 11 and 12 ppt.Total mortality rates at 11 and 12 ppt were 35%and 94%,respectively.After 36 hours of exposure to10,11 and 12 sea water,activity of Na~+-K~+-ATPase increased significantly throughout the experiment(P＜0.05).Within the tolerable salinity range(0-8 ppt),Na~+-K~+-ATPase activity increased at 36 hrs posttransfer,whereas after 36 hrs,Na~+-K~+-ATPase activity declined slowly with increasing time and reached the initial level of obscure puffer embryos before salinity change.2.Changes in activity of the enzyme Na~+-K~+-ATPase and morphology of gill chloride cells in obscure puffer(Takifugu obscurus)newly hatched larvae were investigated after abrupt transfer from ambient rearing conditions(FW and 8 salinity)to different salinities(0,8,10,12,14,16 ppt).Results showed that after an abrupt transfer to the salinities,survival rates and the activity of larvae were high throughout the experiment.Total survival rates of freshwater hatched larvae at 12 ppt reached 91.4%,while the 8 salinity hatched larvae at 10 ppt reached 64.4%. Compared with fertilized eggs,newly hatched larvae can tolerate higher salinity environment.After transfer to salinity,the activity of the Na~+-K~+-ATPase increased significantly(P＜0.05).The Na~+-K~+-ATPase activity values of freshwater hatched group were higher than the 8 salinity hatched larvae.This may be due to 8 ppt hatched larvae had efficient mechanisms of osmoregulation.3 To investigate the efficient mechanisms of osmoregulation in juvenile Takifugu obscurus,obscure puffer were transferred directly from freshwater(FW)to different salinity regimes in the laboratory.The activity of Na~+-K~+-ATPase in gill and kidney and the osmolality of the blood were assayed.Changes in location, number,and ultrastructure of chloride cell were also examined under light and transmission electron microscopy following abruptly transfer.Results showed that gills responded to hyperosmotic shock by an enhancement of NKA activity and plasma osmolality;gill Na~+-K~+-ATPase activity increased significantly as early as 24 h and reached a maximum level at 48h post-transfer.Renal activity of Na~+-K~+-ATPase responded with rapid increase at 6h post-transfer.A significant decline in gill and renal Na~+-K~+-ATPase were found in the experimental group at 192h(P＜0.05).The chloride cells were mostly distributed on the base of gill lamella,or the filament epithelium of the gills.In fresh water,a few chloride cells were present with undeveloped vesicle-tubular system,and apical surface was equipped with microvilli.After 24 hours of exposure to 20 sea water,chloride cells were degenerating with few mitochondria,whereas the tubular network was more developed and dintended at 96 hours.The results suggested that the juvenile obscure puffer appeared to a short-term shock at the beginning of abruptly transfer to higher salinity and then gradually acclimated to the change of salinity by its ability of osmoregulation.After 48 hours of exposure to 30 sea water,the number and volume of mitochondria in chloride cells increased significantly.Some mucous cells were observed close by the chloride cells. |
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