Sixteen isolates of Aeromonas hydrophila isolated from normal, apparently normal and epizootic-ulcerative syndrome (EUS)-affected fish were screened for virulence and production of extracellular proteins (ECP). Results showed that all isolates were virulent to catfish (Clarias batrachus) juveniles inducing dermonecrotic lesions after intramuscular injection. Lesions were characterized by necrosis of the underlying musculature that leads to erosion and sloughing-off of the locally affected tissues. Only seven of the 16 ECP preparations, however, induced similar lesions on test catfish. No clear correlation between virulence and ECP production of EUS-associated A. hydrophila was established.

The dramatic fall in prawn (Penaeus monodon) prices coupled with environmental concerns has resulted in a relative stagnation of prawn grow-out operations in the Philippines. Leaders of the Philippine aquaculture sector are concerned that their cost of production is higher than that of their close competitors in Indonesia and Thailand. Also, the environmental and production crash experienced in Taiwan has led to a general perception that intensive culture cannot be sustained. The sector recently experienced a lack of direction and growth, combined with crowded water sheds, excessive use of water bodies, overuse of groundwater and continued destruction of mangrove. A field survey of prawn growers was conducted in August-October 1992 using a standardized economic questionnaire that included costs, returns and growers perceptions of constraints. Economic estimates were developed for representative production systems; intensive, semi-intensive, extensive and prawn-milkfish rotation. The incentive to expand the prawn pond area is not strong. Existing intensive facilities can be operated efficiently and profitably, but new intensive operations will most likely need to include water treatment capabilities for water entering and exiting grow-out ponds. Canals, reservoirs or ponds used for water quality improvement may be able to concurrently produce a profitable crop, such as milkfish-prawn rotation. Internal rate of return for semi-intensive ponds using earthen ponds was higher than for other culture systems. If, over time, water quality and conservation constraints are sufficiently addressed, stocking densities might be increased. Research and extension programs targeting equity should focus on integrated systems.

Aeromonas hydrophila, isolated from chevron snakehead Ophicephalus (=Channa) striatus affected with epizootic ulcerative syndrome (EUS), was injected intramuscularly into healthy walking catfish Clarias batrachus at varying 10-fold serial dilutions from 10⁸ to 0 colony-forming units (cfu) per fish. Only 10⁶ or more cfu/mL induced dermomuscular lesions. Initial healing of lesions was observed by day 7 but complete healing was not apparent until day 16. Experiments were also conducted on possible portals of entry of A. hydrophila into walking catfish: Intramuscular (IM) injection, gastric gavage, fish food, and immersion of injured fish in rearing water inoculated with the test bacteria. Injuries were caused by skin or muscle cut, dermal scraping or incision, fish bite, and cohabitation of fish with golden snails Ampullarius sp. Only IM injection treatment induced dermomuscular pathology in the test catfish. This suggests that a localization of A. hydrophila to a level of 10⁶ cfu/mL in the musculature must be established for dermal lesions to develop.

Successful rearing of hatchery-reared sea bass, Lates calcarifer, fry in illuminated floating cages was demonstrated in a 42-day experiment. Three feeding regimes, i.e. natural zooplankton (NZ) + minced fish flesh (MFF), NZ alone, or MFF alone and two stocking densities (600 and 1 200 individuals m²) were tested in a 3 × 2 factorial experiment. Fish reared in unlit cages and fed MFF alone during daytime served as the control. Results showed that no interaction existed between stocking density and feeding regime and that the two stocking densities used did not influence fish growth in terms of mean final body size. In general, sea bass reared in lit cages (NZ + MFF and NZ) grew and survived better than the control fish (MFF). However, fish reared under NZ + MFF feeding regime had the highest final mean total length (TL, 42.1 mm) and body weight (BW, 1 311.8 mg) followed by fish reared under NZ feeding regime (mean TL = 26 mm, BW = 415 mg). Fish in the unlit control cages exhibited the poorest growth (final mean TL and BW: 26 mm and 277.6 mg BW). Furthermore, specific growth rates (range: 5.7–8.5% day⁻¹) of fish in lit cages were significantly better than those of fish in the unlit control cages (mean: 3% day⁻¹). Percentage survival (38%) of fish stocked at 600 m⁻² density and fed NZ was not significantly different from fish in the NZ + MFF feeding regime. However, increasing the density to 1 200 ind. m⁻² tended to significantly decrease percentage survival (20%) of fish with NZ feeding. Fish reared in the unlit control cages had the poorest survival of 13–14%. The high percentage composition by number (CN, 88%) of copepods in the stomachs of sea bass fry fed on NZ alone and the equally high percentage feeding incidence (94%) indicated that fish fed sufficiently on natural zooplankton. Supplemental feed using minced fish flesh contributed about 43–59% of the fish diet in addition to natural zooplankton.

A hatchery rearing scheme for the red snapper, Lutjanus argentimaculatus, is described. The feeding regime consisted of Chlorella, Brachionus, Artemia and minced fish. The average survival rate at day 24 was 27% in 3-ton tanks but only 3% in 0.5-ton tanks. From an initial length of 2.15 mm at stocking, larvae grew to 8.2 mm on day 24 and 30.6 mm on day 55. Growth and survival were best when larvae were fed screened Brachionus (<90 μm) during the first 14 days. Larvae fed Artemia at 1, 2 and 3 per ml per day weighed similarly on day 35 but were longer at the higher feeding levels and survived better at the lower levels. Larvae fed Artemia at 2 per ml had a higher survival when the ration was given four times a day rather than 1-2 times a day.

The growth rate of Haliotis asinina fed three diets was evaluated over a 120 day period. Juveniles fed the red alga Gracilariopsis heteroclada and an artificial diet grew faster in terms of both total body weight and shell length than those fed the red alga Kappaphycus alvarezii. Juveniles fed the artificial diet produced more weight than those fed G. heteroclada for the first 90 days, but abalone fed G. heteroclada grew faster from Day 105 onwards. In terms of shell length, the artificial diet produced faster growth rates than G. heteroclada for the first 75 days but from Day 90 onwards, faster growth rates were observed in juveniles fed G. heteroclada. Reductions in daily growth rates of juveniles during the latter phase of the growth trial were attributed to channelling of energy into gonad development. G. heteroclada promoted high growth rates over a long-term period (360 days) and is considered to be best suited for abalone farming in the Philippines.

Fish landings in Malalison Island in the west central Philippines were monitored from February 1991 to January 1992 to determine the types of fishing gear employed, the predominant species caught, the catch per unit effort (CPUE), and the yield from the coral reefs. Fishing was monitored only during the spring tide periods, after a preliminary sampling showed no significant differences among four lunar phases. A total of 494 fishing operations was recorded. CPUE (kg per fisher h⁻¹) by gear was 1.1 for spear guns, 1.4 for spear guns with compressor, 0.4 for set gill nets, 2.4 for drive-in gill nets, 1.2 for drift gill nets, and 0.7 for hook-and-lines. The CPUEs of Malalison gears are similar to those of other coral reef fisheries. Dominant species caught were fusiliers and surgeonfishes by gill net. surgeonfishes by spear gun, and snappers and groupers by hook-and-line. The fish yield from the Malalison coral reefs was estimated to be 5.8 t km⁻² year⁻¹, which is low, and similar to overexploited. reefs in the Philippines and elsewhere. Live coral cover averages 35% in Malalison. Reef degradation, high fishing effort, low yields, and the poverty of the fishing community suggest ‘Malthusian over-fishing’. Community based management and resource enhancement are being initiated by the SEAF-DEC Aquaculture Department to protect and sustain the fishery and improve the economy in Malalison Island.

Five purified microbound diets containing 1% of 18:2n − 6, 18:3n − 3, 20:4n − 6, or n − 3 highly unsaturated fatty acids (HUFA: 60% 20:5n − 3 + 40% 22:6n − 3) in addition to 8% 18:1n − 9, and a control diet containing 9% 18:1n − 9 were fed to milkfish fry or late postlarvae for 30 days (Trial 1) and 35 days (Trial 2). The salinity was 16–17‰ and temperature was 27 ± 1 °C during the culture periods. A completely randomized design with three replicates per treatment per trial was followed. In each trial, 60 fish (5mg, 6mm) were stocked per 301 oval plastic tank and fed the experimental diets at 20% of biomass per day. Survival of 100% observed for all groups in both trials demonstrated that the milkfish fry reared in brackish water utilized the test diets. Specific growth rates did not differ significantly among treatments (P 0.05), with values of 9.5–9.9% and 10.0–10.3% in Trials 1 and 2, respectively. Weight, length and feed conversion ratio of milkfish fry fed the various diets also did not differ significantly (P 0.05). Although not significantly differentiated in Trial 1 (P 0.05), incidence of eye abnormality was highest in milkfish fry fed the 18:1n − 9 diet in Trial 2 (P 0.05).

A feeding trial was conducted to evaluate the potential of replacing fish meal with processed animal by-product meals, meat meal and blood meal (4:1 ratio), in practical diets for juvenile grouper (Epinephelus coioides). Eight isonitrogenous diets were formulated to contain 45% protein and 12% lipid. Fish meal was replaced by 0%, 10%, 20%, 30%, 40%, 60%, 80%, and 100% of meat meal and blood meal (4:1) mixture (diets 1–8). The diet with 100% fish meal (diet 1) or trash fish as feed (diet 9) were used as controls. Grouper juveniles were reared in 250-l circular fiberglass tanks maintained in a flow-through seawater system. Each dietary treatment was tested in quadruplicate groups of 25 fish per tank arranged in a completely randomized design. Fish were fed the diets twice per day at a daily feeding rate of 5–6% of biomass and trash fish at 10–12% of biomass for 60 days. Percentage weight gain, specific growth rate (SGR), survival, feed conversion ratio (FCR) and body composition of grouper juveniles were measured. There were no significant differences (P>0.05) in growth performance among fish fed diets 1–7 (0–80% fish meal replacement) with those fed diet 9 (trash fish as feed). However, fish fed diet 3 had significantly higher (P<0.05) growth than those fed diet 8 (100% fish meal replacement). Survival among fish fed the experimental diets did not significantly differ (96–100%) but was significantly higher (P<0.05) than survival (90%) of fish fed trash fish. These results showed that up to 80% of fish meal protein can be replaced by processed meat meal and blood meal coming from terrestrial animals with no adverse effects on growth, survival, and feed conversion ratio of E. coioides juveniles.

This report describes bamboo back disease affecting Penaeus monodon in the Philippines. Affected and normal shrimps were processed for bacterial isolation and histopathology. Morphological changes in the external anatomy were also noted. The cuticle of the abdominal segments of shrimp with bamboo back disease do not overlap properly which gives them a bamboo-like appearance. The appendages are shorter compared with normal shrimps. No bacteria were recovered from the hepatopancreas, lymphoid organ, and hemolymph thus ruling out bacterial infection. Histopathology shows normal hepatopancreas, but the muscle fibers of the abdominal segments are fragmented and necrotic.