Gonadal maturation, rematuration, and spawning of nine- (1982 stock) and ten-year-old (1981 stock) milkfish reared in 150 and 200 m³ concrete tanks were observed in 1990 and 1991. From 23 September to 9 November 1990, the 1981 stock spawned 15 times with an average daily collection of 61,000 ± 21,000 eggs. From 4 larval rearing trials, the mean overall survival rate (from eggs to 21 -day-old fry) was 9.68 ± 4.3%. From 25 Aril to 31 October 1991, the stock spawned a totaf of 108 times. Mean daily egg collection increasef to 305,000 ± 32,000. Successful rearing trials conducted during the latter part of the spawning season had a mean overall survival rate of 17 ± 3% (n = 17) indicating that mass fry production techniques can be improved. Spawning of milkfish broodstock in concrete tanks provides an alternative to other existing methods of seed production.

Three isocaloric and isonitrogenous diets formulated to contain 12 (diet A), 15 (B) and 18% (C) lipids were tested on hatchery-bred rabbitfish Siganus guttatus broodstock to determine their effect on spawning and quality of the eggs and larvae. The results show that fish on diet C has higher fecundity than those on diets B and A. Also, fish on diet C yielded eggs of better quality than either fish on diets B or A. This was indicated by spawns resulting in higher percentage of normal hatchlings, larger newly-hatched larvae and higher survival rates until the 14th day of rearing. Dietary lipid levels, however, have no remarkable effects on fertilization, yolk and oil globule volumes, hatching rate nor larval size at harvest.

The amount of rotifers and Artemia nauplii consumed daily by the grouper Epinephelus suillus larvae was determined through examination of gut contents. The larvae (2.6 mm TL) were initially fed rotifers on day 2 and newly hatched Artemia nauplii on day 21 (9.1 mm TL). The amount of food consumed by the larvae increased with larval growth. Larvae also showed diurnal feeding pattern at day 7 (3.6 mm TL), day 14 (4.9 mm TL), day 21 (9.1 mm TL) and day 28 (11.1 mm TL). Feeding incidence increased in the evening and became zero at 2100-2200 h. Active feeding started earlier in the older larvae and satiation was between 0900-1100 hr.

Two Nile tilapia strains of Oreochromis niloticus (L.) (Cichlidae, Teleostei) fingerlings were exposed to mixtures of zinc, cadmium and mercury. The two strains used were Chitralada or NIFI (originally from the National Inland Fisheries Institute, Thailand) and CLSU (from the Freshwater Aquaculture Center of the Central Luzon State University, The Philippines). Short-term (10 days) exposure to a metal mixture of 5 mg 1⁻¹ zinc (Zn), 0.5 mg 1⁻¹ cadmium (Cd) and 0.02 mg l⁻¹ mercury (Hg) gave significantly higher survival percentage in the NIFI strain compared with the CLSU strain. Similar exposure conditions using larger and older fingerlings of the two strains also showed a slightly higher survival percentage in the NIFI strain but the difference was not significant. Prolonged exposure of the fingerlings to a lower concentration of the metal mixture (1.0 mg l⁻¹ Zn, 0.1 mg l⁻¹ Cd, 0.01 mg l⁻¹ Hg) also resulted in similar survival percentages between the two strains at the end of the 60 days run. Whole body accumulation of Zn was significantly higher in CLSU than in NIFI after 14-day exposure to the low concentration metal mixture. There was no significant difference in the accumulation of Cd and Hg between the two strains. Of the three metals, Hg had the highest bioaccumulation factor (BF) which was ∼900–1000, followed by Cd with 255–280 and Zn with 180–195 times the nominal concentration in the water. Concentration of Cd and Hg in fish tissues increased with exposure period while the concentration of Zn was maintained in NIFI and decreased in CLSU between the 6th and 14th day of exposure, suggesting that Zn (an essential element) accumulation maybe regulated by both strains.

The hispathological changes in gills of Nile tilapia, Oreochromis niloticus, fingerlings exposed to 5.3 mg/l (96-h LC50) malathion are described. These changes include hypertrophy of epithelial cells after 3 h, epithelial lifting and destruction of the structural integrity of some lamellae after 24 h, multifocal fusion of adjacent lamellae after 72 h, and diffused epithelial lifting after 96 h. Partial to complete recovery was observed in gills after rearing in malathion-free water for 6. to 12 d.

Chanos chanos belongs to a monotypic gonorynchiform family and is most closely related to the freshwater Ostariophysi. The earliest gonorynchiforms occurred in the Cretaceous of Brazil and west Africa. Chanos occurred in the freshwater Eocene deposits of Europe and North America, and probably invaded the circumtropical Tethys Sea during transgression episodes. At present, milkfish occurs near continental shelves and around oceanic islands throughout the tropical Indo-Pacific. Milkfish populations throughout the range show high genetic variation but low genetic divergence, similar to many other commercially important teleosts. The natural life history of milkfish is one of continual migration. Adults are relatively large (to 1.5 m or 15 kg), long-lived (to 15 years), pelagic and schooling. They spawn offshore near coral reefs or small islands. The eggs, embryos and larvae are pelagic and relatively larger than those of most marine species. Larvae ≥ 10 mm long and 2–3 weeks old move inshore via a combination of passive advection and active migration. Passing shore waters and surf zones, they settle in shallow-water depositional habitats such as mangrove swamps and coral lagoons, where they metamorphose and spend a few months as juveniles. Some juveniles may enter freshwater lakes where they grow into sub-adults but do not mature. Both small juveniles and large sub-adults go back to sea when they reach the size limit supportable by the habitat. Little else is known of the dynamics of wild populations of milkfish. A fishery on inshore larvae supports the centuries-old aquaculture of milkfish in southeast Asia. During the past ten years, milkfish have matured and spawned under various conditions of captivity, and hatcheries have produced larvae to supply the culture ponds. Much remains to be learned concerning the milkfish, particularly its ecology and physiology.

This article exhorts university graduate students and researchers everywhere to publish their scientific papers in peer-reviewed journals, preferably those covered by the Institute for Scientific Information (ISI), rather than in the gray literature – technical reports, conference proceedings, and books. Philippine journals are also used to work for stringent peer review, frequent and prompt issues, wide circulation, high standards, and ISI coverage – so that Filipino scientists contribute to, and benefit from, the mainstream literature of the international scientific community.

The ammonia excretion rate was used as an index of the physiological state of Penaeus monodon poltlarvae (PL) by monitoring excretion rates after handling and transfer to physiologically different media. The ammonia excretion rate of postlarval P. monodon increased from a mean of 0.543 µg to 0.815 µg total NH₃-N per mg dry wt per hour after transfer from 32 to 20 ppt sea water. PL transferred to 40 ppt showed a significant decrease in excretion rate to 0.423 µg total NH₃-N per mg dry wt per hour. These changes in excretion rate after transfer to different salinities were only temporary since acclimatized PL showed only minor deviations in excretion rate from the control. PL transferred from normal (8.2) to low (7.2) pH had elevated ammonia excretion rates, from 0.591 µg to 0.733 µg total NH₃-N per mg dry wt per hour, while those transferred to high pH (9.2) had excretion rates that dropped drastically to 0.259 µg. About 40% of the PL in high pH were moribund after the 150 min exposure. The ammonia excretion rate of PL after a 1 hour feeding was twice that of unfed PL during the first 15 min after transfer. This difference narrowed with time and was no longer significant at 75 min after transfer which also the duration that represented the postprandial surge in ammonia excretion after the 1 hour feeding.

Among naturally spawned and hormonally induced eggs of Siganus guttatus, salinity levels, at which at least 90% of the eggs hatched, ranged from 7 to 67 ppt for naturally spawned eggs and from 9 to 67 ppt for hormonally induced eggs. Salinity levels at which naturally spawned eggs yielded at least 50% normal larvae ranged from 7 to 62 ppt; salinity levels providing at least 90% normal larvae ranged from 10 to 51 ppt. Salinity levels at which 50% larvae survived for 12 h after hatching ranged from 10 to 45 ppt, and for 24 h after hatching, from 14 to 37 ppt. From the results, it is recommended that the incubation salinity of S. guttatus be within the range 10–51 ppt, and for yolk-sac larval maintenance, within the range 14–37 ppt.

The effects of burning the varying amounts of dried rice straw on snails and soil properties in brackishwater ponds in the Philippines were evaluated. Cerithium tenellum, Telescopium telescopium and other unidentified snail species present in a drained brackishwater ponds were exposed to heat by burning 1.3, 2.7, and 4.0 kg dried rice straw piled 5, 10, and 15 cm thick in nine 1 m2-plot. While T. telescopium and the unidentified snail species were killed (100%) in all the treatments, C. telellum mortality ranged fro 83±3.75 percent in plots with 1.3 kg straw. The chemical properties of the soil after burning the straw revealed a decrease in the organic matter and available phosphorous and increase in the available iron and potassium. There was no effect of burning on soil pH. The acetate soluble sulfate decreased with 1.3 kg of straw and increased with the higher amounts of straw.