Study Of Pufferfish Takifugu Fasciatus On Salinity Adaptability Under Cultural Conditions

Based on methods of experimental ecology, the biological characteristics of pufferfish T. fasciatus under controlled conditions were studied, with special respect to artificial reproduction, breeding techniques, toxic responses of larvae to common chemicals, and effects of water salinity on food intake, growth, feed utilization, standard metabolism, serum osmolality and digestive enzyme activity. The effects of salinity and protein levels on growth and biochemical composition of T. fasciatus were also investigated. The main results are as follows.1. Reared in water salinity of 8%0, 18%o, 25%o, 35%o and fresh water for 6 weeks, the yearling fish shows no significant differences in feeding rate, growth and food conversion ratio among treatments, except that the mortality in 35%o is 100%. As to 2-year-old fish, growth rate is greatest in 8%o; specific growth rates (SGR) are significant different among treatments; and feeding rate and food conversion ratio are not significantly different.2. After transfer to freshwater directly, the 2-year-old fish pretreated with high salinity shows compensatory growth and higher feeding rate than which with lower salinity. The fish pretreated with 8%o and 18%o shows no significant difference in growth, feeding rate and food utilization.3. In order to estimate the activity of digestive enzyme, T. fasciatus was reared in 8 %o, 18%o, 30%o salinity for 14 days. The results show that salinity can enhance digestive enzyme activity. The optimal salinity of yearling and 2-year-old fish are both 18%o based on amylase activity; Pepsin activities of both ages have a similar variation trend with water salinity; Trypsin activity of yearling fish increase sharply within 2 days in 8%. and then decrease, There is a slight drop followed by an elevation in trypsin activity of 2-year-old fish.4. Standard metabolic rate of 2-year-old fish reared in saline water are higher than that in freshwater and there are no significant differences among three salinities.Standard metabolic rate of yearling fish exhibite a higher level and remained a decrease tendency during the time of 8:00 am to 2:00 pm. After 10:00 pm the metabolism level descend gradually.5. Juvenile pufferfish were reared in 0, 8%o, 18%o, 30%o water salinity to examine growth and food utilization. Fish under each treatment was fed with formulation diets of two protein levels, i.e. 37.7% and 43.2%, respectively for 8 weeks. The results show that the maximum SGR appear in the mesohaline and low protein level group. SGR of the fish fed with diet of high protein level increase with the increment of salinity; SGR of the fish fed with low protein level rise firstly with the increase of salinity and then drop at the highest salinity level. Feeding rates indicate the same variation tendency as that of SGR, and the food conversion efficiency (FCE) has a minimum value (61.3%) which appears in freshwater and low protein group, and a maximum of 83.9%, which is in 18%o and high protein level group. The dry matter content of fish body has a positive relationship with salinity. According to the present results, the suitable salinity to the juvenile is 18%o and optimum dietary protein content is about 37.7%.6. Gonad of reared T. fasciatus can become mature under controlled conditions without migration. Survival rate of larva 15 days after hatched is 70%.7. Feeding rate decrease from 12.6% to 2.6% when fish body weight ranges from 12.2 g to 213.2 g.