Induced spawning and larval rearing of domestic hybrid striped bass (Morone saxatilis x M-chrysops) in Taiwan

This is the first study on the induced spawning and larval rearing of capti ve F-1 hybrid striped bass (Morone saxatilis x M. chrysops) in Taiwan. Impo rted fry of F-1 hybrid striped bass were held in an earthen pond and fed ex clusively commercial floating pellets. They reached sexual maturity at two years old and were successfully induced to both strip spawning and tank spa wning by a single hormone injection. Human chorionic gonadotropin (HCG), at a dosage of 300-400 IU/kg, was the most effective treatment. Low doses of HCG (200 IU/kg) or LHRH-a (lutenizing hormone releasing hormone analogue; 3 0 mu g/kg) alone were moderately effective, while groups injected with 10 m u g/kg LHRH-a, or saline and the untreated control did not spawn. In terms of the fertilization rate, hatch rate and level of larval deformities, no s ignificant difference was found between tank spawning and strip spawning. F ertilization rates ranged from 76.3% to 96.7% and hatch rates were between 1.6% and 24.2%, whereas the level of larval deformities ranged between 19.2 % and 100%. Hatched larvae were reared in 2 m(3) circular fiberglass tanks and fed init ially on rotifers and Artemia nauplii, followed by daphnia, and finally con verted to fish starter crumble. Two batches of larvae were reared and survi ved to the juvenile stage (7.3-7.9 cm TL) in 1996. Larvae developed to the juvenile stage 21-28 days after hatching and measured 12.10 to 18.24 mm TL. The juveniles reached a mean total length of 7.5 cm after 77 days of reari ng with an average survival rate of 2.65%. The F-2 progeny exhibited a low hatch rate, low survival, high level of deformities and growth variability which suggests that F-2 progeny may not be suitable for culture.