Experiments were conducted to determine the optimum dose of luteinizing hormone-releasing hormone analogue (LHRHa) and pimozide (PIM) injected simultaneously to yield a high ovulation rate and produce sufficient eggs in the Asian catfish Clarias macrocephalus. In June 1990, injection of 0.05 or 0.10 μg LHRHa/g body weight (BW) + 1 μg PIM/g resulted in 100% ovulation, while only 80% of gravid catfish injected 0.025 μg LHRHa + 1 μg PIM/g ovulated. Most of the eggs stripped from 6 out of 8 control fish were not mature. Fertilization and hatching rates of LHRHa + PIM-induced fish (75–90% and 39–51%, respectively) were higher than those of control fish (36–39% and 0–1% respectively). In August and September 1990, at gravid catfish ovulated after injection of 0.05–0.10 μg LHRHa + 1 μg PIM/g BW. However, only 20% of the fish given 0.025 μg LHRHa/g + 1 μg PIM/g BW in August ovulated. No eggs could be striped from any of the control fish in August and September 1990. Techniques developed in this study, showed a simple and effective way of spawning captive catfish, C. macrocephalus. A simultaneous intramuscular injection of 0.05 μg LHRHa + 1 μg PIM/g and stripping of eggs at 16–20 h post-injection have been tested to yield high ovulation, fertilization and hatching rates.

Nile tilapia were fed diets supplemented with one of the following lipid sources at 5% level: cod liver oil, corn oil, soybean oil, a coconut oil-based cooking oil or a combination of cod liver oil and corn oil (1 : 1). The control diet had no lipid supplement and tad fish meal as a sole protein source. A diet with soybean meal as a protein source was also tested. The number of females that spawned, spawning frequency, number of fry per spawning, and total fry production were increased at varying degrees by the supplemental lipid sources except for the cod liver oil. Fish fed the soybean oil diet tad the best overall reproductive performance over a 24-week period. Fish fed the cod liver oil diet had the highest weight gain but the poorest reproductive performance. The suplemental lipids significantly increased crude fat levels in the liver and ovaries. Both males and females Ld the cod liver oil diet had the highest levels of fat in the liver and muscle. The ratio of total n-6/n-3 fatty acid in the liver, ovaries and testes was influenced by the supplemental lipid sources. It was highest in fish fed either the soybean oil diet, the corn oil diet, or the soybean meal diet and lowest in fish fed the control diet or the cod liver oil diet.

A survey was conducted among 72 seaweed (Kappaphycus sp.) farmers in the Western Visayas region, Philippines, from March to July 1990 to assess their culture practices in terms of production and economic efficiency. Yields of 5.8 tons/ha per crop (dry weight) and 7.6 tons/ha per crop (dry weight) were obtained from bottom line and raft monoline methods, respectively. Investment requirement was P27361/ha for bottom line culture, and P56757/ha for raft monoline culture (P25=US$1). The bottom line method was more profitable with net farm income of P33286/ha per crop compared with P26365/ha per crop for the raft monoline method. The bottom line method of culturing seaweed is more cost-efficient compared with the raft monoline method. Production cost averaged P3.32/kg for the former method, and P5.55/kg for the latter method. Return on investment was also higher at 243% for the bottom line method and 93% for raft monoline.

The use of suspended (hapa) nets as nursery enclosures for shrimp fry was tested. In the first trial, four stocking densities (72, 144, 288, and 432 fry m⁻³) of P. monodon fry (PL₂₀, body weight = 8 mg, body length = 12.6 mm) were evaluated in 1×1×1.5 m hapa nets. Results showed that shrimp BW, BL, and survival rates were inversely related to stocking density. Shrimp fry stocked at 72 fry m⁻³ attained significantly greater BL of 22 and 37 mm and BW of 50 and 260 mg after 15 and 30 days, respectively, and survival of 92%. A verification trial using PL₂₈ (BW = 10 mg, BL = 13.2 mm) at a stocking density of 288 fry m⁻³ in hapa nets of 2×3×1.5 m yielded a mean survival of 97%, BL 48.1 mm, and BW 780 mg. Hapa nets are therefore useful as alternative shrimp fry nursery systems in the absence of specialized tanks or pond nursery facilities.

The survival rates of Penaeus monodon nauplii, protozoea and mysis abruptly exposed to salinity of 12, 16, 20, 24, 28, 36, 40 and 50 ppt were determined and compared. Larvae kept at 32 ppt, the spawning or initial rearing salinity, served as the control. The effect of the salinity treatments on the rate of metamorphosis of each larval stage was also investigated by determining and comparing the time needed for 50% of the larvae to molt to the succeeding stage (MT50). Results showed that at the naupli stage, significantly higher (P<0.01) survival was obtained at 32 and 36 than at 28 ppt. However, survival at 28 ppt was still significantly higher than in the rest of the treatments. The MT50s at salinity levels of 28 to 36 ppt were similar. At the protozoeal stage, similar survival and MT50 values were obtained at 28 to 40 ppt. In all other test salinities, total mortality of the protozoea occurred. Within the salinity range of 20 to 36 ppt, the mysis exhibited similar survival rates but metamorphosis was significantly faster at 28 and 32 ppt, as shown by the lower MT50 values.

Many inland water bodies in the Philippines are currently used for fish cage culture. Inappropriate practices including feed management in aquaculture results not only in the degradation of water quality but also in economic losses for the fish farmers. The effect of two feeding management schemes on the production of cage-cultured Nile tilapia Oreochromis niloticus (Linn.) in Lakes Bato and Buhi in Camarines Sur Province and Laguna de Bay in Rizal Province were studied. Daily (DAILY) and skip-feeding (SKIP) schemes using the same daily ration based on standing biomass were used. Mean final weight and daily growth rate were 18% higher in DAILY compared with SKIP in Lake Bato. No significant differences in both parameters were observed in tilapia reared in the two feeding treatments in Lakes Buhi and Laguna de Bay. Condition factor, survival and final yield did not show any significant differences in both treatments in all three lakes. Significant differences in feed conversion ratios (FCR) were observed between the two treatments with SKIP having 36% lower feed conversion ratio (FCR) in Lake Bato and 41% lower FCR in Lake Buhi and Laguna de Bay compared with the DAILY treatment. The results suggest that skip feeding is an economically and ecologically viable alternative to the cage culture of Nile tilapia in cages.

Gracilariopsis heteroclada thalli were planted in a 1 m2 ditch along a drainage canal at Leganes, Iloilo, Philippines. Monthly growth rate and production were calculated to determine the effect of harvesting on the regeneration capacity of the plant. After 30-day growth period, all plants were harvested at 25%, 50%, 75%, and 100% of the total available biomass. Though highest growth rate was observed at 100% (8.7%), it took three months for the plants to regenerate and obtain a considerable biomass. Positive growths were obtained when plants were harvested at 75% (5.6%) during the entire growth period. Negative growth rates observed both at 25 and 50% harvests.

With attractive prawn export prices and the availability of hatchery fry and commercial feeds, Philippine aquaculture has experienced a shift from milkfish to prawn Penaeus monodon and an intensification from traditional and extensive prawn culture to higher stocking densities. This paper features the results of a survey of intensive prawn farms (n = 21) in Western Visayas and Northern Mindanao conducted in 1990. Average farm size, production, feeding and water management are described. To solve the self-pollution characteristic of intensive ponds, the farms utilized some 40 chemical and biological products; at least another 35 were available in the market at the time of the study. These include therapeutants and disinfectants, soil conditioners, bacteria-enzyme preparations, algicides and piscicides, plankton growth promoters, and feed additives. The possible ecological effects of effluents drained into adjacent marine waters are discussed; some recommendations are given.

Mature male rabbitfish (Siganus guttatus Bloch) received weekly injections of 200 μg of luteinizing hormone-releasing hormone analogue (D-Ala⁶, Pro⁹-LHRH-ethylamide) per kg body weight for 5 consecutive weeks. Mean spermatocrit, or packed sperm volume (27–51%), and mean sperm density (\(3.2–9.6\times10^{6}\) spermatozoa per kg body weight) decreased significantly 24 h after each injection. The amount of expressible milt (mean: 5.8–11.7 ml per kg) in response to weekly injections of LHRHa increased significantly relative to saline-injected fish (1.0–2.9 ml per kg), but only during the initial 4 weeks of regular hormone treatment. Three weekly injections of LHRHa likewise augmented mean sperm production (\(29.2-112.5\times10^{9}\) spermatozoa per kg) in rabbitfish. However, no significant enhancement in sperm production by LHRHa-injected fish was observed over the last 2 weeks of hormone injection. These results demonstrate that weekly injection of LHRHa can sustain milt production in mature rabbitfish, although their capacity to produce spermatozoa is limited to only 3 consecutive weeks of regular hormone treatment.

Growth of fry from three test strains of Nile tilapia (CLSU, ISRAEL and NIFI) fed restrictively and nonrestrictively were compared. Four-week old fry were matched for size with similarly aged red tilapia fry which served as an internal reference. Fish were stocked in 60l aquaria at a ratio of 25 tests:25 reference fish. Test fish were fed commercial fish feed ad libitum during the initial and final two weeks and rations of the same feed at 10% of the fish biomass during weeks 3 and 4. Control fish were fed commercial fish feed ad libitum throughout the six week experiment. Although feed restriction retarded growth in all three test strains, growth differed significantly between strains. Under both restrictive and nonrestrictive feeding regimes, the ISRAEL strain grew better than the CLSU and NIFI strains.