A detailed account is given of milkfish farming procedures generally practised in the Philippines. The following phases are identified: 1) collection and/or procurement of seed for fry phase; 2) fry rearing; 3) culture and production in grow-out ponds; 4) milkfish culture and production in freshwater fish pens. Harvesting and post-harvest handling are described. Problems and constraints of milkfish farming in the Philippines are also examined.

Recent developments in milkfish breeeding include succesful induced spawning of wild^1,2 and captive^3-5 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.

Various farming systems for prawn and shrimp are compared, with emphasis on the extensive and semi-intensive culture of tiger prawn Penaeus monodon and white shrimp Penaeus indicus in monoculture or in polyculture with milkfish (Chanos chanos). The bases of comparison include pond design characteristics, stocking density, food supply, water management, average production, technical, and other major input requirements. Common factors that may influence production for each system are also discussed. It is observed that prawn and shrimp production has been mainly characterized by the extensive system. Of the 200,000 ha of brackishwater fishponds in the Philippines, about 25% (50,000 ha) are stocked with prawns and shrimps in monoculture or in polyculture with milkfish. Only a relatively small portion (less than 500 ha) of the area is utilized for semi-intensive culture. The dramatic increase in area utilization for extensive prawn production in recent years can be attributed to high market demand, increased hatchery-bred fry production, minimum technical requirements, and lower production cost and risks. The trend towards intensification among existing large fishfarms is hampered by rising capital costs for fishpond improvement and increasing operational expense and risks. However, intensification is gaining some attention and progress in limited areas, primarily to maximize utilization and production to avoid high investment cost of land for expansion. Further development and progress in the industry will be dependent on such factors as market price, availability of fry and feed at reasonable cost, supply of trained technicians, technical problems, financial situation, and economic viability of the operation.

This study is conducted to develop a sampling program and to determine the optimum stocking density for Artemia production in earthen ponds.

The use of yeast as feed in aquaculture is discussed. It has been successfully used as feed for Penaeus japonicus larvae, for Brachionus plicatilis mass culture, and for the improvement of nutritional quality of Tigriopus japonicus. It has been found most effective as supplemental food when enough phytoplankton cannot be supplied.

Natural populations of oysters and mussels have long been gathered for food by coastal communities in the Philippines, and bivalve farming began in early 1900. The first farms were no more than a series of bamboo poles inserted in the muddy bottom of Manila Bay in Bacoor Cavite. In May 1934, the Bureau of Fisheries and Aquatic Resources (BFAR) established a pilot oyster farm in Binakayan, Cavite Province, Luzon, and a lucrative industry soon grew up. By 1950, about 200 ha of private farms existed in Bacoor Bay, but, in the late 1950s, mussels appeared on the farms and threatened the industry. The response of BFAR was to initiate farms for mussels, and the results prompted the establishment of a mussel industry that proved to be at least as lucrative as the oyster industry. Farming of windowpane oysters (Placuna placenta) began in the late 1940s in the tide flats of Bacoor Bay, the delicate, translucent Placuna shells being used for window glazing and shellcraft. In the early 1970s, however, the bay became increasingly polluted, the stocks could not survive, and they are still not found in the waters of the bay.

The freshwater prawn Macrobrachium abounds in the rivers, lakes and estuaries of the Philippines. At SEAFDEC, Binangonan Research Station, a few preliminary studies have been conducted on Macrobrachium sp. and M. rosenbergii . A recent preliminary survey of nearby river systems showed that there is a big demand for Macrobrachium in the market.

For hatchery production of Penaeus monodon and other penaeid fry, the SEAFDEC Aquaculture Department is dependent mainly on captive broodstock in the form of ablated females, using up to 1,500 spawners in one year. The availability of such broodstock has enabled us to gather information on the reproductive biology as well as broodstock techniques for P. monodon and other species. This paper discusses studies on courtship and mating behaviour, fecundity, egg quality and rematuration; and requirements for induced maturation (source and age of stock, sex ratio, feeding, tank management, etc.) of P. monodon. A comparison of biological and construction requirements of two broodstock systems — land-based tanks and marine pens — is made. Work on other penaeids, mainly P. indicus is discussed. Lastly, areas for future research on penaeid maturation are highlighted.