The status of the Philippine mangroves is examined, the functions of mangrove areas are highlighted, the threats to mangrove resources are identified, and the prospects for sustainable use are discussed. The Philippines harbour 39 species of true mangroves belonging to the following genera: Acanthus, Camptostemon, Lumnitzera, Excoecaria, Pemphis, Xylocarpus, Aegiceras, Osbornia, Nypa, Aegialitis, Bruguiera, Ceriops, Kandelia, Rhizophora, Scyphiphora, and Sonneratia. The fauna is equally diverse. Apart from fish and shrimp, other animals collected from mangroves are crabs and lobsters, bivalve and gastropod molluscs, and other invertebrates. Mangrove services include coastal protection, erosion control, sediment stabilization, flood regulation, nutrient supply and regeneration, waste treatment, and wildlife habitats. Mangroves could be valuated at around 10,000 US$/ha/year. As elsewhere, it can be expected that the net present value is highest if the mangrove cover is maintained. The decline of mangroves from about 500,000 ha in 1918 to only 120,500 ha in 1994 was caused by overexploitation by coastal dwellers and to conversion to settlements, agriculture, aquaculture, salt pans, and industry. The remaining mangroves should be conserved. It is recommended to establish the following zones: (1) protected forest; (2) productive forest; (3) reforestation areas; and (4) conversion areas.

Shrimp monoculture systems have been beset with devastating losses due to infectious diseases and environmental deterioration. On a global scale, efforts to make shrimp culture a sustainable industry are warranted because of the high value and demand of shrimp. A Code of Practice for Sustainable Shrimp Farming prepared by the Global Aquaculture Alliance has been adopted by various shrimp producing countries addressing issues like mangroves, site evaluation, design and construction, feeds and feed use, shrimp health management, therapeutic agents and other chemicals, general pond operations, effluents and solid wastes, and community and employee relations. Shrimp hatcheries have benefited from technological advances in practically every aspect of rearing including implements to control water quality, eliminate pathogens, and improved nutrition through innovative artificial feeds and supplements. These technologies have made postlarval production very successful, although in many cases, high survival cannot exactly be equated with good quality. Thus a closer look at hatcheries is essential to ensure that rearing protocols match the conditions to which postlarvae will be exposed to upon stocking in ponds. Compiled information on the estimated number of hatcheries and forms in major shrimp growing areas in Asia show a relatively smaller number of small independent hatcheries compared to farms, which demonstrates that effective disease control programmes need to emanate from hatcheries. Presently, three programmes for the hatchery need serious attention. These are (a) the continued implementation of fry analysis procedures, not only as a marketing tool, but so as to exclude pathogenic organisms from ponds, (b) adherence to agreed-upon codes of practice and conformity with accepted guidelines on live transfers to minimise disease spread, and (c) development of a reliable source of domesticated broodstock and incorporating specific pathogen free (SPF) and specific pathogen resistant (SPR) stocks in these programmes to minimise or eliminate dependence on wild broodstock. One of the main constraints is the lack of cost-effective and efficient methods to prevent and correct environmental deterioration, and to maintain biosecurity. In addition to providing primary health care, disease control strategies should be a combination of pathogen exclusion and environmental management: the former for primary pathogens such as viruses and the latter for secondary pathogens like bacteria, whose pathogenicity is heightened by environmental degradation and lowered resistance of shrimps. Shrimp forming should start employing systems to manage and lessen waste and the outflow of organic pollutants that could contribute to self-pollution or deterioration of the quality of receiving waters. These include improved feeds and conversion ratios to make feed utilisation more economical and efficient, implementation of recirculating or zero discharge technology, improving the efficiency of aeration systems, improvement of pond siting, understanding of the pond ecosystem and the role of microbes in the environment. In addition to implementing disease control measures and ensuring product quality in various industry sectors, approaches need to be welded together for a holistic approach to health management.

Researches on marine shrimp diseases for the past three years centered primarily on the diagnosis and control of viral and bacterial infections as well as nutritional, toxic and environmental diseases. Diagnostic techniques developed or adopted recently for prawn viruses include the ELISA technique for detecting baculoviruses, acridine orange fluorescence, eosin flourescence and in vitro culture of the Penaeus monodon-type baculovirus (MBV) on lymphoid organ-derived monolayer culture. Studies have been conducted on the identification, pathogenicity and chemical control of bacteria causing luminous vibriosis and shell disease. Investigations on non-infections diseases such as the chronic soft-shell syndrome, blue shrimp disease and aflatoxicosis elucidated the factors responsible for the development of these diseases. Current research on marine shrimp diseases, other related problems and recommendations are discussed.

Philippine aquaculture production mostly comes from pond culture (brackishwater) constituting 47% of the total 1987 production of 560,970 t followed by mariculture of seaweeds, mollusks and finfishes. Fishponds have increased from around 61,000 ha in 1941 to 210,400 ha at present while the 130,000 ha of remaining mangroves constitute only 13-26% of the original area. The effects of aquaculture on the coastal environment are apparent in the decline in nearshore fisheries production and loss of services (typhoon buffer, flood control, soil stabilization). Mangrove conversion into ponds, species introductions and transplantations, spread of parasites, pests and diseases, increased organic nutrient loading, use and release of chemicals, sedimentation, extraction of groundwater, and salinification of soil and water supplies, are the identified aquaculture-related practices that lead to the degradation of nearshore resources. Some ecological effects also have social repercussions. Recommended measures to solve these problems include: rationalized use of mangroves and mangrove reforestation; regulation of groundwater extraction, import/ use of chemicals, disposal of organic wastes, and introductions/transplantations; research (bacteriology of aquaculture facilities, effects of organic wastes, effects of sedimentation, effects of chemicals on marine organisms including antibiotic resistance, etc.); training and extension; and improvement of interagency coordination.

Juveniles of Haliotis asinina, 10 mm shell length were subjected to four photoperiodic regimes namely, 6L:18D, OL:24D, diffused 12:12D, and ambient light (12L:12D) serving as control. Juveniles were fed fresh seaweed, Gracilariopsis bailinae, in excess amounts throughout the experiment. At the end of a 105-day experiment, juveniles held under ambient photoperiod were significantly bigger and had higher average daily growth rate than the rest of the treatments. Feed conversion efficiency was higher at ambient light than at other photoperiodic regimes. Daily feeding rates at 65-day culture period were similar for all treatments; however towards the end of culture period, feeding rate of abalone at ambient light was lowest compared to the rest of the treatments. Percent survival was significantly higher in animals at ambient light and at 6L: 18D with 99% and 97% respectively, than at other photoperiodic regimes.

Newly hatched trocophore larvae of the abalone haliotis asinina linne were stocked at densities of 1000, 3000 and 5000 larvae/1 at low (20-25^oC) and high (ambien, 28-30^oC) water temperature levels in light (transparent) and dark (black cloth-coered) lass container. Larvae were reared in UV light-irradiated sea water until pre-settement stage. Aeration was not provided during the 20-h incubation periond. A 3x2x2 factorial design with three replicates per treatment was folloed. A three-way analysis of variance (ANOVA) showed a significant interaction among the factors tested. Analysis at each density level showed that at stocking density of 1000 larvae/1, no significant difference between temperatures and between light or dark condition was observed. However, at densities of 3000 and5000, significantly higher survival was obtained at low, than high temperature (P<0.05), but no difference between the light and darck conditions. Analysis at each temperature showed that, at high temperature,better survival was obtained at stocking density of 1000, than higher densities (P<0.001), and at light than at darck condition (P<0.05). However, at low temperature, no significant difference between light abd darck conditions was detected. ANOVA at light or darck condition showed that at any of these conditons, larvae survival was always higher at 1000 stocking density that t other density (P 0.05). Survival was not significntly different between stockng density of 3000 and 5000 larvae/1 at any of those light conditions. Theredore, during incubation of newly hatched trocophore larvae of H. Asinina to pre-settlement stage, the optimum stocking density at high temperature (28-30^oC) was 1000/1, in a light-penetrable rearing container. When reared at higherstocking densities of 3000 or 5000, a higher survival was obtained when temperature was lower to 20-25^oC in either rearing conditions tested.

Mass fish kills in Laguna de Bay, the largest lake in the Philippines, has been reported as early as in the 1930’s. With the introduction of and development of aquaculture in this lake, considerable attention and concern was focused on the problem. Records of mass fish kill in the lake mainly from unpublished sources and reports from fisherfolk were reviewed and the causes categorized. The data covered the period 1972 to 1998. Among the commercially important fish species affected were milkfish (Chanos chanos), Nile tilapia (Oreochromis niloticus), bighead carp (Aristichthys nobilis), snakehead (Channa striata), catfish (Clarias macrocephalus and C. batrachus, Arius manilensis), silver perch (Terapon plumbeus) and goby (Glossogobius giurus). The first three species are widely used in aquaculture and the rest are important in open water fishery. Sixty percent of mass fish kill incidents were due to low dissolved oxygen with more than half of these cases associated with blue-green phytoplankton blooms. Fish kills due to pollution from agriculture and industries, fish pathogens and other causes are also discussed. The incidence of mass fish kill reached its peak between 1977 to 1986. Records show that the most number of fish kills (80%) occurred between the months of May to September. The lakeshore towns in the central arm of the lake had the highest incidence of fish kill reported with 46% and followed by the west arm of the lake with 38% of all fish kills recorded.