Mollusc research at the Aquaculture Department of the Southeast Asian Fisheries Development Center started in 1975 and focused on two commercially important mangrove-associated bivalves, the slipper-shaped oyster (Crassostrea iredalei) and the green mussel (Perna viridis). Studies conducted were on spatfall forecasting to increase collection of seeds from the wild; improvement of farming techniques; seed production in the hatchery; bivalve sanitation; and transplantation. These studies have led to the development of a suitable spat collector for oyster and mussel; promotion of the raft culture method for oysters and mussels to prevent siltation of growing areas, including a low-cost raft design for this purpose; refinement of transplantation techniques to increase production and to grow osyters and mussel in suitable areas without natural populations; and desgin of a prototype low-cost depuration unit. A socio-economic study of oyster and mussel farming practices in Western Visayas provided information on current farming practices and profitability. A study done on the use of green mussel as biofilter in a semi-intensive shrimp pond showed that shrimp stocked with mussels grew faster than those without. A study on the biology and fishery of the "imbao" Anodontia edentula, another mangrove-associated bivalve, is ongoing. Spawning has been achieved in the laboratory and larval stages monitored were first polar body, 2-cell stage, morula, ciliated gastrula, trocophore, veliger, and pediveliger.

The intensification of aquaculture in the Philippines has made the use of chemicals and biological products inevitable. A recent survey conducted nation wide among shrimp and milkfish culture facilities revealed the use of more than 100 products for rearing, prophylaxis, and treatment purposes. The most commonly applied chemicals are disinfectants, soil and water conditioners, plankton growth promoters, organic matter decomposers, pesticides, feed supplements, and antimicrobials. All of these are readily available in the market. The dosages, purposes, patterns of use, origins, and manufacturers of these chemicals and biological products are discussed in this paper. The indiscriminate use of chemicals has caused mortalities and morphological deformities in the host and development of antibiotic-resistant bacterial strains. The use of chemicals in aquaculture also poses dangers to public health. Government policies regulating or prohibiting the use ofcertain chemicals for aquaculture have helped curtail the destructive consequences of chemotherapy. Moreover, research institutions have geared their studies towards discovering environmentally safe drugs and other alternatives to disease control. However, these efforts will be futile unless a strong and aggressive campaign on the cautious and restricted use of drugs in aquaculture is conducted among shrimp and fish farmers, drug manufacturers and suppliers.

Fish pathology as a discipline was of relatively minor importance in the early years of SEAFDEC/AQD because technologies for producing aquaculture commodities were still being developed and high-density fish rearing activities were minimal. With fast adaptation of technologies developed locally and elsewhere and their modification to suit industry needs, disease problems started to occur. Disease develops through the interaction of three important factors: the host, the pathogen or disease agent, and the environment. In most high-density aquaculture rearing units, the environment exerts pressure on the host and favors the pathogen. When the host's defenses are overwhelmed, a disease condition is created which may result in death. Mortalities are often equated to economic losses, and research in fish diseases then becomes significant. Research has the ultimate aim of preventing disease occurrence.

The Feed Development Section at SEAFDEC/AQD conducts research on the nutritional requirements and the development of costeffective practical diets for regionally important fishes (milkfish, tilapia, carp, and sea bass) and shrimp (Penaeus monodon). Macronutrient requirements for protein, lipid, carbohydrate, energy, and optimum dietary protein to energy ratio have been defined. Essential fatty acids required by each species have been identified. Requirement levels for the ten essential amino acids in milkfish and tilapia have been established. In shrimp, requirements for other essential nutrients like phospholipid and cholesterol are known. Dietary calcium and phosphorous requirements of shrimp have been determined. Requirement for water-soluble vitamins and bioavailability of stable forms of vitamin C are being evaluated. However, much work remains to be done on the vitamin and mineral requirements of cultured species. The major digestive enzymes, proteases, carbohydrases, and lipases in milkfish have been studied. Further, the apparent digestibility of commonly used feedstuffs were determined in-vivo and in-vitro for milkfish, and presently, for shrimp and sea bass. In diet development, the formulation of supplemental grow-out feeds from inexpensive indigenous materials has been emphasized. Likewise, artificial diets for larvae and broodstock are being developed. Effects of feed additives like chemo-attractants and antioxidants were studied. In addition, studies on feed and feedstuff quality control and application of proper processing techniques are being pursued. At present, there are supplemental grow-out diets for the fishes that are commercially viable. Diets for all life stages (grow-out, larval, and broodstock) of shrimp are available. Improvement of these diets will continue as more information on the nutrient requirements are known.

The success of a fish culture operation depends, in part, on adequate supply of seed for hatchery and grow-out. The culture and husbandry of many of Southeast Asia's marine fish species are constrained by the unreliability of seed supply which are seasonally gathered from coastal areas. To augment the natural seed supply and decrease the dependence on wild catch, SEAFDEC/AQD has undertaken studies to develop a captive source of breeders for some of the economically important marine fish species in the region. This paper presents a brief update of the status and recent advances in marine fish broodstock development undertaken by SEAFDEC/AQD.

Commercially important penaeids of the closed thelycum group belong to five subgenera of the genus Penaeus — Penaeus, Fenneropenaeus, Marsupenaeus and Melicertus that are almost exclusively Indo-West Pacific and Farfantepenaeus that is predominantly Western Atlantic. Since the ablation of Penaeus duorarum more than a decade ago, the first for any penaeid, around 23 species have been matured in captivity, 17 of them belonging to the closed thelycum subgenera (P. aztecus, P. brasiliensis, P. californiensis, P. duorarum, P. esculentus, P. indicus, P. japonicus, P. kerathurus, P. latisulcatus, P. merguiensis, P. monodon, P. notialis, P. orientalis, P. paulensis, P. penicillatus, P. plebejus, and P. semisulcatus). The complete spectrum of controlled reproduction in penaeids covers maturation, spawning, hatching of eggs into viable larvae, and the production of postlarvae to constitute the next batch of broodstock. The full closing of the cycle has been achieved in at least six closed thelycum species whereas gaps, e.g. inability of mature females to spawn or nonhatching of eggs, remain for the others. Spawners or mature females used in commercial hatcheries and research laboratories are either wild-caught or matured in captivity with human control ranging from nil to a regular closing of the cycle. Wild spawners may be spawned directly after capture and transport or subjected to environmental manipulation, e.g. thermal control to induce or inhibit spawning. Females matured in captivity may come from wild broodstock (adults and subadults caught from estuaries or "sourced" by trawlers from offshore waters) or captive (pond- or tank-reared) broodstock. Introduced or exotic penaeid species must depend on a pond- or tank-reared broodstock whereas indigenous prawns and shrimps may be constituted from wild or captive broodstock. There are three basic approaches employed singly or in combination to induce ovarian maturation in penaeids — endocrine, dietary or nutritional and environmental. Endocrine manipulation has so far been synonymous with unilateral eyestalk ablation, a technique with far-reaching impact on penaeid aquaculture. Closed thelycum penaeids may be classified into those that require ablation in order to mature and those that do not. To a third group belong species that have been experimentally induced to mature with and without ablation. Diets for maturation include fresh and frozen animal sources (mussel, clam, oyster, squid, marine worms, shrimps, fish) and formulated pellets given in any combination. The choice of marine worms and mollusks is based on their high levels of arachidonic, eicosapentaenoic and docosahexaenoic acid, the dominant fatty acids found in mature ovaries and testes. Environmental parameters studied in relation to maturation include light (intensity, quality and photoperiod), temperature, salinity and pH. Although a regular closing of the cycle has been achieved for some, the state-of-the-art for most penaeids is the successful production of larvae and postlarvae from either wild spawners or wild immature/spent females matured/rematured in captivity. The improvement of reproductive performance including larval quality from captive broodstock remains a major area for future research and includes the determination of minimum age and size for maturation. The complete description of the nutritional and environmental requirements for maturation should lead to the development of alternatives to ablation such as photoperiod manipulation or the use of reproductive hormones. The present focus on characterizing the physicochemical and dietary requirements for maturation should be extended to other phases of reproduction: mating, spawning, fertilization and hatching. Studies on biology (molting, mating, fertilization including the cortical reaction) and biochemistry (maturation stages) provide baseline information for designing maturation tanks and formulating broodstock pellets. Investigations of wild stocks complement laboratory studies in elucidating the interrelationships among molting, mating, maturation and spawning. Manual spermatophore transfer is being developed to solve the problem of nonmating in closed (and open) thelycum species. This technique will also be useful in future hybridization work, together with in vitro fertilization.

In any aquaculture system, the major components are seed and feed. The same is true for Penaeus monodon known locally as sugpo, lukon, pansat or by its trade/export name "black tiger". This paper is an attempt to give a state-of-the-art of prawn hatchery technology and wild fry collection in the country, focus on technical and non-technical problems, and offer solutions and policy recommendations.