A guide to the establishment and maintenance of milkfish broodstock

The manual describes methods used at the SEAFDEC Aquaculture Department in order to establish milkfish broodstock. It is presented under the following major section headings: Establishing broodstock farms; Farms for rearing bangus juveniles; Maturation cages for rearing broodstock to maturity; Gathering data; Spawning and egg collection; and Larval rearing.This study as well as the publication of this guide was partly supported by the International Development Research Centre of Canada under Project No. 3-P78-0033 (Phase II) and No. 3-P81-0171 (Phase III)

Spontaneous maturation and spawning of milkfish in floating net cages

Contribution No. 165 of the Aquaculture Department, SEAFDEC.Milkfish (Chanos chanos Forsskal) reared from wild-caught fry and from hatchery-bred fry matured at 3.5-5.5 years (2.3-4.9 kg). Maturation and spawning of the hatcherybred fish marks the first time the milkfish life-cycle has been completed in captivity. Milkfish at various stages of gonadal development were obtained in July-October 1980 and March-June 1981 derived from wild-caught fry, and in February-June 1983 from the hatchery-bred fish. The fish were held in floating net cages 9 m and 10 m diameter by 3 m deep, located in 7 m deep water off Igang, Guimaras Island, Philippines. Annual ranges of temperature and salinity were 25-33°C and 25-38 ppt, respectively. The fish were fed commercial feed pellet (42% protein) at 1.5-2% of body weight twice daily. Sexual maturation occurred during the natural breeding season of wild milkfish in the nearby waters. Gonadosomatic index (GSI) of mature males was 0.32-3.95 (wild-caught, 0.32-3.95; hatchery-bred, 1.71-3.85). For mature females it was 1.24-8.12 (wildcaught, 1.56-7.62; hatchery-bred, 1.24-8.12). Two spawnings were recorded in August 1980 and eight in May-July 1981 from the broodstock derived from wild-caught fry, with 342-6293 eggs collected from each spawning, while 14 spawnings were observed in May-June 1983 from the hatchery-bred fish, with 770-114 000 eggs collected. The time of spawning was between 23.00 and 02.00 h. Fertilization rate was 55-99% for the broodstock from wild-caught fry and 47-100% for the hatchery-bred fish. Hatch rate varied from 9 to 80%. Factors affecting spontaneous maturation, spawning and rematuration are discussed. Although slight improvements in egg collection were obtained, further innovations in egg collecting techniques will have to be developed. The results indicate the potential for hatchery production of milkfish fry from captive broodstock and for restocking of waters deprived of naturally occurring fry

Problems associated with hormonal induction of gonad development in milkfish (Chanos chanos)

Recent developments in milkfish breeeding include succesful induced spawning of wild1,2 and captive3-5 fish and spontaneous spawning of broodstock.6 Gravid spawners, however, are available only during the wild or are reared in captivity. The seasonal and uncertain supply of wild fry is a major constraint in efforts to increase production of this important food fish in the Philippines, Indonesia, and Taiwan. Gonad devepolment can be induced in some fish by hormone administration. This has been recently reviewed by Lamp7 and other workers.8,9 Induced gonad development using purified salmon gonadotropin have been reported in Salmo gairdneri,10 Oncorhynchus gorbuscha,11,12 and Mugil cephalus.13,14 Hormones are usually administered by injection at frequent intervals in these studies. To reduce stress from frequent handling, a slowrelease hormone cholesterol pellet was with success in Salmo auratus and Ophicephalus striatus.16 Recent literature suggests that vitellogenesis in fish (at least yolk granule or gobule formation) is under control of estrogen and a pituitary factors. Estrogen stimulates the liver to produce vitellogenin, while the incoporation of vitellogenin into oocytes requires a pituitary factor which may not be the glycoprotein (Con A II) gonadotropin.7 In the light of this information and in anticipation of a synergistic role of thyroid hormone ,17 a combination of fish pituitary extract, estrogen and thyroxin was used in some of our experiments. Our attempts to induce gonad development in sexually immature milkfish and rematuration of regressed fish have not been sucessful to date. This paper presents the experiments done and discusses factors possibly contributing to the negative resp[onse in this fish