Dietary vitamin A,ascorbic acid and α-tocopherol affect the gonad development and reproductive performance of starry flounder Platichthys stellatus broodstock

The present trial was conducted with starry fl ounder Platichthys stellatus broodstock to evaluate the effects of dietary vitamin A,ascorbic acid,and α-tocopherol on the gonadal development and reproductive performance.8 000 IU/kg diet vitamin A(VA group),500 mg/kg diet ascorbic acid(Vcpp group),or 250 mg/kg diet α-tocopherol(α-TA group)was added into basal diet to create 3 vitamin experimental diets,respectively.Each diet was fed to 450 starry fl ounder broodstock for 104 days.Samples were collected weekly.The gonadosomatic index(GSI)of 3 vitamin experimental groups fi rst decreased and then increased.Maximum GSI of Vcpp group was higher than that of α-TA group but lower than that of VA group.The spawning periods of 3 vitamin experimental groups lasted 49,56,and 45 days,respectively.No mature eggs were observed in the control group during the trial.The absolute fecundity(AF)and relative fecundity(RF)of α-TA group was higher than that of Vcpp group but lower than that of VA group.The results suggest that different vitamins play different roles in the fi sh reproductive process.Vitamin A stimulated the maturation of the ovary,ascorbic acid prolonged the spawning period,and α-tocopherol affected the development of the eggs.     

Viral diseases of olive flounder in Korean hatcheries

In order to elucidate the state of diseases, especially viral diseases, and to prevent viral diseases from occurring in olive flounder hatcheries, a range of studies, including epidemiological study, were performed from 1997 to 2003. The location of the hatcheries investigated includes several representative sites in the east （Kangnung, Uljin, Pohang, Yangsan, Ulsan, Pusan）, south （Wando, Changheung, Goheung, Yeosu, Namhae, Tongyeong, Geoje, Jeju） and west （Seosan, Kunsan, Gochang, Yeongkwang, Mokpo, Chindo） costal areas of the Korea Peninsula. A total of 2000 cases have been examined in 7 years, in which mortality caused by viral agents accounts for 22%, or 446 cases. Mortalities associated with viral infection considerably increased from 14% in 1997 to 27% in 2003. A variety of viral diseases were observed, and the occurrences of viral epidermal hyperplasia, viral ascites and viral deformity, viral nervous necrosis, and hirame rhabdoviral disease are 14%, 51%, 25%, and 8% respectively. By investigating the viral infection of broodstock flounder, the infection rate of marine birnavirus （MABV） in hatcheries was identified to be approximately 30%, therefore, it is highly necessary to acquire and keep non-infected broodstock fishes.