Fry collection and induced spawning
Although it is reported that mature spawners caught from the wild have been observed to spawn in captivity (Hussain et al., 1975) and accelerated sex-reversal and induced spawning have been achieved experimentally (Chen etal., 1977), wild fry are still used for cagefarming. Fry measuring 3.5–5 cm are available during the north-east monsoon and fishermen collect them with small seines and transport them for sale to fish culturists.
Observations seem to indicate that a female E. tauvina will take more than five years tobecome a functional male. By oral administration of methyltestosterone incorporated into feeds three times a week over a period of two months, at a dose of 1 mg per/kg body weight, two- to three-year-old fish yield milt on induced breeding (Chen et al., 1977). Induced spawning of three-year-old females and sex-reversed males has been achieved by injection of HCG and pituitary gland extract from chum salmon or white snapper. Complete ovulation was also obtained by a single injection of 5000 IU HCG. The fertilized eggs can be hatched in tanks within 23–25 hours at a temperature of 27°C. Spawning can be carried out throughout the year, depending on the stage of gonadal development. The larvae metamorphose into juveniles of around 25 mm length in about 33 days. Fifty-day-old juveniles measure up to 70 mm in length.
The red grouper has also been induced to spawn in captivity and the larvae reared under experimental conditions, following more or less the same techniques as employed for the estu-arine grouper.
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