The levels of estradiol-17β, and progesterone in the hemolymph, ovaries and hepatopancreas, in relation to the vitellogenin levels of captive female Penaeus monodon, were determined during the gametogenic cycle. Estradiol in the hemolymph was detected in fully mature shrimps (Stage 5) only. The ovarian estradiol levels were quite variable but showed no significant differences in the mature (Stages 4 and 5) and spent stage (Stage 6). In the hepatopancreas, a peak in estradiol level was noted in mature shrimps (Stage 5). The progesterone levels in the hemolymph were high in shrimps with mature ovaries (Stages 4 and 5) while those with immature ovaries (Stages 2, 3 and spent) were low or undetectable. The progesterone levels in both ovaries and hepatopancreas were significantly high in mature shrimps. The vitellogenin levels increased simultaneously with ovarian development and reached maximum levels during the final stage of vitellogenesis. A decrease in levels was observed after egg release. The correlation between the levels of progesterone and vitellogenin may indicate a positive effect of this steroid on vitellogenin production.

Lethal toxicity tests of ammonia at different pH levels (7, 7.5, 8, and 8.5) and its effect on survival and growth of the early larval stages of Penaeus monodon were determined. An increase in ammonia toxicity when the water pH increased was revealed in 96 h toxicity tests. Estimated LT50 decreased from 101.09 to 25.16 h for protozoea exposed to 8 ppm ammonia, from 115.79 to 11.26 h for mysis exposed to 24 ppm, and from 51.41 to 22.58 h for PL exposed to 52 ppm ammonia with increase in pH levels. The effect of 3 and 6 ppm ammonia levels at pH levels of 7.0, 7.5, 8.0 and 8.5 on the survival and growth of P. monodon larvae and postlarvae was also investigated in a 16-day sublethal toxicity test. Results indicated that ammonia at 3 and 6 ppm affects both survival and growth of shrimp. Survival was decreased by 27% in 3 ppm and by 48% in 6 ppm ammonia, while growth was reduced by 4.4% in 3 ppm and by 6.5% in 6 ppm ammonia. Increasing pH of the rearing water resulted in significantly lower survival in protozoea, mysis, and postlarval stages. No interactive effect of pH and ammonia was detected.

The comparative morphology of the foregut during development from embryonic larva to adult in Cherux quadricarinatus was examined by light and scanning electron microscopy. Major ontogenetic changes occurred in the gastric mill dentition in terms of denticle shape, appearance of vertical ridges in the lateral teeth, roughness of masticating surfaces, degree of sclerotization and proportional sizes of the median tooth components. Natural food types appropriate for the various life history stages during artificial rearing of C. quadricarinatus may be inferred from the morphology of the gastric mill dentition of those stages. Cardiopyloric valves and the gland filter appeared prior to development of functional gastric mill teeth. Compared with the foregut of adult astacid crayfish, that of adult C. quadricarinatus shows differences in the ventral cardiopyloric valve, pyloric funnel and lateral valves.

One-day old sea bass larvae (0.93-2.03 mm total length, 0.94-1.00 mg wet body weight) were stocked at a density of 30 larvae per liter in nine 250 l capacity fiberglass tanks. Fish were reared for 26 days on three different feeding regimes using Brachionus plicatiilis, Artemia salina and Moina macrocopa as live foods. Delaying feeding of Artemia nauplii until day 15 resulted in slower larvae growth rates compared with fish fed Artemia starting on day 10. Partial replacement of Artemia nauplii by Moina starting on day 17 showed a marked increase in larval growth over the delayed Artemia treatment. Percent survival of larvae amongst all three treatments did not vary significantly.

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.