The milkfish, Chanos chanos Forsskal, does not reach gonadal maturity easily in captivity. In an attempt to induce maturation, exogenous hormones, LHRH-A and 17α-methyl-testosterone, were implanted into adult milkfish either alone or in combination. The hormones were delivered using cholesterol pellets (LHRH-A) or silastic tubing sealed with elastomer (17α-methyl-testosterone). The fish were implanted three times at monthly intervals between March and May of 1985. The combination of LHRH-A and 17α-methyl-testosterone induced significantly more maturing fish (P < 0.05) than LHRH-A alone or sham controls; 88%, 38%, and 13%, respectively. Fish with average egg diameters between 768 μm and 905 μm, spawned 48 h after hormone implantation. These results indicate that the maturation and spawning of milkfish in tanks can be induced and accelerated 1–2 months earlier than the beginning of the normal spawning season through hormone implantation.

The spawning behavior and embryonic and larval development of Siganus guttatus are described from laboratory observations. Characteristic prespawning behavior began 4 h before actual spawning: the female touched the anal region of the abdomen on the bottom of the tank; the male displayed short, jerky, rushing movements towards the female, often with rapid circling around her. The male and the female separately released small amounts of milt and eggs several times during the pre-spawning ritual. The color of both sexes changed, the male becoming lighter and the female darker in ground color. Spawning took place at 02.30 h on the third day after the first quarter of the moon. During actual spawning, the pair swam side by side, with the female slightly ahead of the male. Fertilized eggs were small (0.56±0.008 mm), demersal and adhesive, with many oil globules. Larvae measured 1.74±0.043 mm total length at hatching, and possessed eight pairs of free neuromasts with long cupulae (60–180 μm) from 6 h to 39 h after hatching. The adult complement of fin ray counts was attained on day 16 when larvae (=juveniles) measured 8.34 mm total length on the average.

1. Osmolality and chloride concentrations in the hemolymph of Penaeus monodon became stable 1 day after molting in 32 ppt, while total protein and calcium concentrations remained stable throughout the molting cycle. When intermolt (≥ 36 hr postmolt) animals were transferred from control (32 ppt) to experimental (8–40 ppt) salinities, osmolality, chloride and total protein, but not calcium, concentrations in the hemolymph achieved steady state values 24–48 hr after transfer. 2. The hemolymph osmolality was a linear function (slope = 0.28) of medium osmolality at salinities between 8 and 40 ppt. It was isosmotic to seawater at 698 mOsm (10 g prawns) and 752 mOsm (30 g), and was hyperosmotic to the medium below isosmotic concentrations, and hypoosmotic to those above. 3. Hemolymph chloride concentration was isoionic to seawater at 334 mM, and was hyperregulated below isoionic concentrations, and hyporegulated to those above. 4. P. monodon maintained its hemolymph calcium concentration between 6.4 and 10 mM when medium salinities increased from 8 to 40 ppt. 5. Total protein concentration in the hemolymph was independent of medium salinity (8–40 ppt) and hemolymph osmolality (540–850 mOsm).

Experiments were conducted to determine the tolerance of Siganus guttatus eggs to salinity changes. In the first run, the female was induced to spawn spontaneously by using human chorionic gonadotropin. The fertilized eggs were transferred to seawater of salinities ranging from 8 to 40‰ either at the blastomere or at the gastrula stage. In the second run, the eggs were stripped from the female and artificially fertilized following the dry method. Results indicated that eggs transferred at gastrula stage were more tolerant to salinity changes than those transferred at the blastomere stage. Hatching occurred at all salinities but was highest at 24‰. Percentage of viable larvae was highest at 24‰ and lowest at 8‰. The larvae that hatched at low salinities were relatively longer than those that hatched at ambient and higher salinities.

The paper discusses the effect of stocking density and holding periods in stunting milkfish fingerlings in brackishwater ponds using twelve units of 144m² earthen ponds. With 15, 20, and 25 fingerlings/m² growth and survival rates were not significant (P<0.05) averaging 13.60g and 83.47%, respectively. Lowest survival (54.52%) and growth rates (10.80g) were obtained in treatment with highest density level of 30 fingerlings/m². Using the density of 20 fingerlings/m² different stunting periods of 6, 9, and 12 months were tried. Survival and growth rates were not significant for 6 and 9 months stunting periods averaging 79.98% and 13.21 g. At longest (12 months) stunting period however survival was lowest (52.05%). In stunting milkfish fingerlings, a density of 15 to 25 pcs/m² could be tried at a stunting period of 6 to 9 months in order to obtain an optimum survival of 81.7% and growth rate of 13.4 g.

This paper provides basic early life-history information on milkfish (Chanos chanos), seabass (Lates calcarifer) and rabbitfish (Siganus guttatus) which may explain in part the observed differences in their survival performance in the hatchery. Egg size, larval size, amount of yolk and oil reserves and mouth size are all greater in milkfish than in seabass, and greater in the latter than in rabbitfish. During the first 24 h after hatching, rabbitfish larvae grow much faster than milkfish and seabass larvae at similar ambient temperatures (range 26°–30°C, mean about 28°C). The eyes become fully pigmented and the mouths open earlier in seabass and rabbitfish (32–36 h from hatching) than in milkfish (54 h). Seabass larvae learn to feed the earliest. Yolk is completely resorbed at 120 h from hatching in milkfish, and yolk plus oil at 120 h in seabass and 72 h in rabbitfish at 26° to 30°C. Milkfish and seabass larvae have more time than rabbitfish to initiate external feeding before the endogenous reserves are completely resorbed. Delayed feeding experiments showed that 50% of unfed milkfish larvae die at 78 h and all die at 150 h from hatching. Milkfish larvae fed within 54 to 78 h after hatching had improved survival times: 50% mortality occurred at 96 to 120 h, and 10 to 13% survived beyond 150 h. Unfed seabass larvae all died at 144 h, while 6 to 13% of those fed within 32 to 56 h after hatching survived beyond 144 h and well into the subsequent weeks. Unfed rabbitfish larvae all died at 88 h, while 7 to 12% of those fed within 32 to 56 h after hatching survived beyond 88 h. A delay in initial feeding of more than 24 h after eye pigmentation and opening of the mouth may be fatal for all three species.

Nine practical diets were formulated and prepared as dry pellet crumbles. These were fed to two batches of Nile tilapia fingerlings (0.753g initial mean body weigt for trial I, and 0.961g for trial II) at 10% of fish biomass daily for eight weeks in glass aquaria or wooden tanks. Diets 1, 2, 3 and 4 contained 20% crude protein (CP), diets 5 and 6 had 25% CP and diets 7, 8 and 9 had 30% CP. Mean weight gains were significantly different (P<0.05) among treatments in trial I and in trial II. There were also significant differents in weight gains of tilapia fingerlings fed diets of the same protein level. Diets with higher protein content did not necessarily produce better growth. Irrespective of the protein level, diets containing 18% or more fish meal (diets 3, 6, 7 and 8) gave higher weight increases compared to those containing 0 and 5% fish meal (diets 1, 2, 4, 5 and 9). Diets with ipil-ipil leaf meal or copra meas as sole or major protein source gave the lowest growth response. Of the nine diets, diet 6 produced the highest weight gain followed closely by diets 7 and 3 in both trials. Diets 6, 7 and 3 contained fish meal, soybean meal, copra meal and rice bran, among others. Feed conversion values were also better for these diets.

Four batches of Azolla were grown in cages in Laguna lake between 1981 to 1983. Percent increase in weight per day ranged from 35% (Feb. 24 - March 2, 1981) to 5% (May 8 - May 12, 1983.) Best growth was attained during the cold months. Acceptability of Azolla as supplemental feed for tilapia was determined in four experiments conducted between 1981-1984. The stocking densities varied in the four experiments: 25/m², 50/m², 100/m² and 150/m². All the results showed increase in mean weight of tilapia fed with fresh Azolla over the unfed control. Statistical analysis showed significantly high (p<0.05) mean weights of tilapia fed with Azolla in two experiments only.

A species of Anabaena was isolated from the fronds of Azolla pinnata by combining the chopped fronds of the Azolla extract with either lake water or an organic medium (duck manure alone or combined with banana stalk) and sterilizing at 121°C and 15 psi for 20 min. Growth of Anabaena sp. was observed within 33 to 37 days and compared with the morphology of A. azollae squeezed from the fronds of Azolla pinnata. Results were discussed regarding the high temperature tolerance of the recently isolated Anabaena sp. Anabaena sp. was incubated in synthetic sponge carriers and grown in different media. The total nitrogen contributions of Anabaena sp. in lake water and in nitrogen-free inorganic medium was 22.3 and 13.2 mg/l respectively after 60 days.

Static 96 h bioassays were conducted on milkfish fingerlings at concentrations ranging from 1.00 to 1.80 mg/l KMnO₄. Histopathological analyses of gills, liver, and kidney tissues revealed significant changes even in non-lethal concentrations tested. Damage became severe with increasing concentration and longer exposure to the chemical. Partial to complete recovery was observed in gills, liver, and kidney cells of fish exposed to KMnO₄ for 96 h and then maintained in KMnO₄-free seawater for 240 h.