Shrimp hatcheries are high-density systems and are prone to diseases. A small-scale and a large-scale hatchery for the tiger shrimp Penaeus monodon in Iloilo, Philippines were monitored over two months for water quality and shrimp survival. Water quality (water temperature, pH, salinity, dissolved oxygen, and specific gravity) was not significantly different between the two hatcheries. However, the small hatchery seemed to favor survival of eggs to early postlarval stages, whereas the large hatchery favored the survival of late postlarvae. The normal microflora and bacterial loads of tiger shrimp eggs, larvae, postlarvae, and rearing water were determined to identify the dominant bacteria and potential pathogens. Shrimp eggs harbored the lowest heterotrophic bacterial counts. The counts increased from the nauplii to the mysis stages, decreased during the mysis stage, and then gradually increased in the older larvae. Bacterial loads in the rearing water reflected those in raw sea water and reservoir-aged sea water. Vibrio, Pseudomonas, and Aeromonas were not detected in eggs but were found in postlarvae. Ubiquitous in sea water, these bacteria increased with the build-up of organic matter. The bacterial load in the water adversely affected larval survival. Forty bacterial strains were isolated from tiger shrimp eggs, larvae, postlarvae, from the feeds, and from the rearing water. These were tested for biochemical characteristics and segregated into eight groups or genera. Six genera were found in the mysis and five genera in the postlarvae. The Vibrio species were dominant. Only Escherichia spp. were present in feeds, whereas five genera were present in the rearing water. Only Vibrio and Pseudomonas were present in both larvae and water. Moraxella, Aeromonas, and Klebsiella were found in larvae but not in rearing water. Micrococcus and coryneforms were found only in rearing water. Four Vibrio isolates were tested for virulence against shrimp postlarvae at inoculation densities of 10² and 10⁷ cfu/ml. The four Vibrio species caused mortality of postlarvae, and more at the higher inoculation density. The most virulent was Vibrio anguillarum—30% of postlarvae died after 24 h exposure to a bacterial density of 10² cfu/ml, and all larvae died after 48 h at 10⁷ cfu/ml. Shrimp hatcheries must have protocols for hygiene and sanitation and for disease prevention and control.

Domestic effluents, or waste waters from human settlements, were sampled from eight stations along Imbang River in Negros Occidental from July 1993 to February 1995. Three types of domestic waste waters were produced by communities along Imbang River. Waste waters from clothes washing, house cleaning, and bathing, including washings of domestic animals and holding pens and run-off from rains and storms were conveyed by open canals and ditches to the river. This type of domestic effluents were well aerated and had the least potential to degrade the rivers. Waste waters from kitchens and markets carried large volumes of food scraps and other solid wastes, were unsightly, and smelled bad from the decomposition of garbage. Overflows from septic tanks were the most objectionable domestic effluents with offensive visual and olfactory properties. Domestic effluents had pH 4–7.6, dissolved oxygen of 0.5–7.2 ppm, and biochemical oxygen demand ranging from 2 to 240 ppm. The overflows from septic tanks were of the worst quality, with BOD 20x greater than household washings, and 6x more than kitchen and market effluents. Fecal coliform bacteria made up 93% of the total coliforms in the septic tank overflows, 86% in kitchen and market waste waters, and 39% in household washings. The domestic effluents from the communities around Imbang River had higher than allowable levels of BOD and solids. The 11 barangays with 16,486 households and 85,535 people loaded about 3,4000 m3 of waste water into the river every day. Along with the waste water were 180 mt/yr of BOD, 590 mt/yr of total solids, plus large quantities of nutrients, surfactants, and fecal coliform bacteria.

The contribution of shrimp farm effluents to the pollution load in Imbang River, Negros Occidental was measured during the period May 1993 to February 1995. Shrimp pond effluents were characterized and the pollution load estimated. The pond effluents had low average nitrite (0.0025 ppm) and nitrate (0.06 ppm) and optimum (for shrimp culture) pH 7.9, phosphate 0.15 ppm, dissolved oxygen 5.20 ppm, and salinity 23.3 ppt. Ammonia was 0.13 ppm on average in most farms, above the safe level for shrimp, and total suspended solids was 23 ppm, about 2.5x the allowed limit for effluents. Biochemical oxygen demand (20 ppm) and settleable solids (0.15 ppm) were still with acceptable limits. Residues of organochlorine pesticides were present at very low concentrations, well below the safe levels for aquatic life. Most of the pollution load came from the regular water exchanges over the 4-month crop cycle, at least every two weeks in low-density farms and more frequently in the high-density farms. The total draining of pond water at harvest contributed a minor load. Total solids from shrimp farms contributed a huge load, about 181,325 mt/yr. Total suspended solids contributed 1,285 mt/yr and settleable solids <1 mt/yr. The total BOD load was 154,367 kg/yr. The phosphate load was about 1,080 kg/yr, and the total nitrogen load was 1,225 kg/yr. The effects of effluent release from farms were localized. Upstream water quality and other uses of the river were not affected. Since most of the shrimp farms were located 1.5–2 km from the sea, the release of effluents during water exchange and at harvest did not adversely affect water quality downstream of these farms. Where such draining increased the levels of ammonia, phosphate, and total suspended solids in the river, the effect was significant only within 250 m from the release point, and the pollutants were dissipated about 550–800 m downstream The other water quality variables were at low levels in the pond effluents and did not affect the river water during draining. Often the concentrations of pollutants in the river were higher before than during draining of pond effluents. Stations upstream of the release sites of pond effluents often had high pollutant concentrations from other upstream sources.

An ecological assessment of Imbang River in Negros Occidental was undertaken from December 1992 to February 1995. The effluents from sugar mills, households, shrimp farms, sugarcane plantations and rice fields were characterized and their pollutant loads estimated. Water quality and invertebrate assemblages were analyzed at several sites along the river to determine the environmental status. Results showed significant seasonal and site variations in water quality along Imbang River. The dry season, coinciding with the milling season, was the more critical time of the year as water quality tended to deteriorate. The segments of the river near the sugar mills and households had the poorest water quality. Sugar mill effluents had high water temperature (average 33oC but as high as 50oC), low dissolved oxygen, high total solids, the highest settleable solids (average 2.5 and as high as 17 m/l), and the highest biochemical oxygen demand (average 259 ppm but as high as 14,800 ppm BOD). Domestic effluents had low pH, high ammonia, very high BOD, plus detergents or surfactants and high levels of fecal coliform bacteria. Agricultural runoff had high nitrate, high total solids, and the highest total suspended solids (average 296 ppm but as high as 5,095 ppm TSS). Shrimp ponds used saline water of average 23 ppt, and had the highest total solids (average 23,456 ppm and as high as 57,400 ppm). By far the major contributor of pollutant loads into Imbang River was agriculture, due to its huge areal extent and huge volume of water use and run-off. Agricultural run-off carried the highest annual loads of 7,858 kg phosphate; 6,495 kg ammonia; 794 kg nitrite; 67,212 kg nitrate; 16,987 metric tons settleable solids; 16,800,000 mt total solids, and 11,890,000 mt total suspended solids; but only 297 mt BOD. Sugar mill effluents had the highest BOD load (1,583 mt/yr) and also had high nutrient loads. Household effluents contributed the second largest loads of solids next to agriculture, and also added surfactants (966 kg/yr) and fecal coliforms into the river. The six shrimp farms at the lower reaches of Imbang River were a minor contributor of pollutants into the river, annually adding about 891 kg ammonia; 1,077 kg phosphate; and 181,325 mt total solids.

Skipjack tuna Katsuwonus pelamis and yellowfin or albacore tuna Thunnus albacares taken by hand lines from the 'payaw' off La Union and Ilocos Sur were sampled from April 1994 until August 1995. Skipjack ranged from 28 cm to 59 cm in fork length and from 0.35 to 4.2 kg in weight. Yellowfin ranged 24–67 cm and 0.25–6.4 kg. The common size landed was about 40 cm for both species. Size at first maturity of skipjack was about 41 cm in males and 42 cm in females. The yellowfin tuna taken by hand lines were almost all immature except two mature males about 60 cm long. About 18 prey species were identified in the stomachs of skipjack, and about 25 prey species in yellowfin. The preferred prey were mantis shrimps and squids. Small fishes and other invertebrates were also eaten. Mesopelagic lanternfish were eaten by yellowfin and epipelagic jellyfish were eaten by skipjack.

Fish assemblages on the reef slope, reef flat, and seagrass beds on Santiago Island were sampled over 18 months in 1992-1993 as part of a 6-year reef monitoring project started in 1986. Abundance and species diversity were analyzed by a variety of indices, and by multi-dimensional scaling and correlated ordered similarity matrix. The monitoring showed a distinct shift in the reef slope fish composition during the first half of 1988. Of the 100 most abundant species, 21 species showed significant reductions in abundance, and 20 species showed significant increases. Differences were not due to depth preference or feeding habits. Fishing pressure was apparently responsible for declines in Cheilinus trilobatus, Acanthurus nigricauda, and Naso literatus, as well as a general decline in the family Acanthuridae (surgeonfishes). However, analysis of site preferences of the decreasing species and the increasing species indicated a shift in community composition from those species preferring more coral cover to those preferring more sand, rock, and possibly Sargassum seaweed. Site preferences were determined from benthic life form transects done in 1992. Of 35 significantly changing species for which habitat data was obtained, 24 fit the hypothesis of habitat change. This supports the proposition from previous studies that the major cause of change in the reef slope fish community was the destructive fishing activity associated with Malthusian overfishing. Similar analyses of the fish assemblages on the reef flat and on the seagrass beds showed seasonal effects, particularly in the latter, but no strong shift comparable to that of the reef slope. These latter areas had been subjected to greater fishing pressure for a longer period. Reef fish populations such as those in Bolinao tend to be highly resilient provided the larval supply is not adversely affected. However, subtle changes in the cover of coral on a reef can lead to major changes in the composition of the fish community. Coral cover is being widely diminished on Philippine reefs, and substantial changes in the fish communities may be anticipated, even on reefs with initially low coral cover. These changes may affect the utility and immediate value of the fish to local fishers and the market systems they supply. It is of great urgency to stop destructive fishing practices such as blasting and use of cyanide, and to develop anchoring methods that are minimally destructive. There is a strong predictive relation between the numbers of fish (abundance) in an area and the numbers of species (biodiversity) they include. As fish populations decline due to destructive fishing, or highly concentrated non-destructive fishing, the local species richness may be expected to decline. This decline may have serious short-term social and economic consequences, as well as far-reaching long-term environmental effects. Efforts to reduce overfishing must be intensified—though reduction of birth rate, provision of alternative livelihoods, and curbing of destructive fishing — in order to prevent a very distressing future for the Philippine marine environment and the people it supports.