Penaeus monodon postlarvae, PL, with mean weight and mean total length of 0.57 mg and 6.5 mm respectively, were stocked in aerated aquaria at 20 litre⁻¹ of seawater. They were fed minced shrimp meat at rates of 10, 50, 100, 250, and 500 mg litre⁻¹. Aquaria with diatoms as feed served as control. Growth and survival rates were examined at each feeding level. Water quality parameters measured were dissolved oxygen (DO), ammonia (NH₄-N) and nitrite (NO₂-N) nitrogen concentrations and 5-day biochemical oxygen demand (BOD5). Growth of postlarvae was similar at all feeding levels and greater than the controls. Survival rate at the lowest feeding level was better but not significantly higher (P > 0.05) feeding level of up to 50 mg litre⁻¹ proved to be satisfactory for both growth and survival. Beyond this level, accumulation of organics, low DO, and build-up of metabolites caused a rapid deterioration in water quality. Even at sub-lethal levels a combination of adverse environmental conditions imposed stress upon the cultured organisms and decreased survival rates.

Preliminary field culture of Gracilaria using vegetative fragments inserted between braids of ropes suspended vertically inside a floating cage was undertaken to assess the daily growth rate and monthly yield as influenced by three different spacing intervals. Daily growth rate of cuttings at 10 cm intervals ranged from 0.6 to 7.2% with yields of 11 to 415 g m^-1 line¹, those at 15 cm from 1.4 to 9.1% with yields of 18 to 502 g m^-1 line^-1, and at 20 cm from 1.7 to 10.5% and with yields of 20 to 379 g m^-1 line^-1. Both growth and yield were minimum in December at all spacing intervals but maximum in April at 10 and 15 cm and in February at 20 cm. Results of the analysis of variance (ANOVA) showed a non-significant interaction between spacing interval and culture month on daily yield of Gracilaria. This indicates that the effect of spacing interval on the daily growth rate and monthly yield was not significantly influenced by the culture month; likewise the effect of culture month did not differ significantly with the intervals used. The main effects, however, of spacing interval and culture month to daily growth rate were significant. Yield was significantly affected by the culture month but not by spacing interval.

Sexual maturation in bighead carp Aristichthys nobilis reared without supplemental feeding in floating cages in Laguna de Bay was observed year-round. Percent maturation ranged from 3 to 94% in females and 0 to 82% in males from July 1985 to July 1986. High maturation rates in both sexes occurring in March 1986 were positively correlated with high inorganic turbidity in the lake. Low natural food productivity (phyto- and zooplankton) during high turbidity did not negatively affect fish growth. Fish may have depended partly on suspended particles as additional food sources when production of more suitable food (zooplankton) was low. Increased production of natural food as a result of water clearing by seawater intrusion during May to September did not enhance growth and maturation of the fish. There was a low negative correlation between chlorinity and percent maturation of both sexes.

Milkfish fry were reared to fingerling size in freshwater ponds. For the first experiment, fish were fed the blue-green algae Oscillatoria inoculated and grown in the ponds, Oscillatoria supplemented with a fishmeal-based formulated diet, and the formulated diet alone. Twelve 50-m² earthen ponds were prepared to enhance growth of the indigenous natural foods. Acclimated wild milkfish fry were stocked randomly at 90/m² and were fed for 6 weeks. Milkfish fed the formulated diet alone had a significantly higher (P<0.05) mean weight gain (1.314±0.201 g) than milkfish given the combination of Oscillatoria and formulated diet (0.882±0.230 g). Growth was lowest for fish fed Oscillatoria alone. The feeding treatments in the second experiment were: combination of Spirulina powder and formulated diet, formulated diet alone, and rice bran alone. The stocking rate was equivalent to 91.5–92.5 fry/m² and feeding lasted for 7 weeks. All feeds promoted some growth but the milkfish fed the formulated diet alone invariably had the highest weight increment (1.504±0.167 g), followed by fish given the feed combination (0.881±0.140 g). Rice bran alone gave the lowest growth response. For both pond experiments, growth trends of the young milkfish were similar to those grown under laboratory conditions. Although survival rates were significantly different in one aquarium experiment, survival rates of milkfish in ponds did not differ significantly (P>0.05) among treatments.

Through quantitative determination of the gut content of wild milk fish (Chanos chanos) juveniles, the study aimed to evaluate the food preference of the fish in relation to its availability in the pond so that necessary measures can be taken to provide such food to the feeding organisms. Wild juveniles of milkfish and plankton samples were collected in a mangrove lagoon at Nabunut Island. Various types of food organisms found in the mangrove plankton samples and food components in the gut of milkfish were then tabulated and compared. The gut content of the fish examined showed a preponderance of detritus, plant debris and fine sand particles. These organic materials without mixture of live food organisms were found in 64.5% of the fish collected. Other food ingested consisted of live food organisms but their proportion in the gut was smaller compared to the proportion found in the natural environment. Milkfish juveniles, upon entering depositional environments, prefer to feed on detritus. The pathway of energy flow in the kind of environment is for the food to pass through a detrital chain before being utilized by milkfish. The functional concept and evidence of this pathway is not restricted to natural ecosystems but may also prevail in pond environments.

1. A female specific protein (FSP, vitellogenin) in hemolymph and its related ovarian protein (vitellin) of Pandalus kessleri were studied by means of electrophoretical and immunological procedures. 2. The vitellin was purified from vitellogenic ovaries using hydroxylapatite, DEAE cellulose and Sepharose 6B columns, consecutively. 3. The vitellin had a molecular weight of approximately 560 kD and was composed of two subunits, 81 and 110 kD, respectively. 4. The vitellogenin concentrations in the hemolymph increased as vitellogenesis in the ovarian oocytes advanced and dropped markedly after the release of mature eggs.

Prawns (Penaeus monodon) were obtained from ponds in Iloilo, Philippines, in 1984 and 1985 and maintained in salinities from 8 to 44‰. Total hemolymph calcium was largely affected by molt stage and less so by salinity. A sharp, transient increase in hemolymph calcium occurred 3 to 6 h postmolt, followed by an equally rapid decrease from 6 h postmolt to intermolt. This biphasis response was limited to prawns in 8, 20 and 32‰S; in 44‰S, hemolymph calcium remained the same throughout the sampling period. Peak concentrations of total calcium were greater in low (8 and 20‰S) than in high salinities. Salinity had no effect on the duration of molt cycle nor on time of occurrence of molt. Almost half of molting incidents occurred between 18.01 and 0.00 hrs, and one-third between 0.01 and 06.00 hrs.

Different larval stages of Penaeus monodon were fed with increasing densities of Tetraselmis sp. to evaluate the relationship between food density, ingestion rates, development and growth of Penaeus monodon larvae. Ingestion showed a saturation response to food density. This served as a basis for determining maximum ingestion rates and incipient limiting levels (ILL), defined as the lowest food density to provide maximum ingestion rates (McMahon and Rigler, 1963). Both ILL and maximum ingestion rate increased as larval stage progressed, with maximum ingestion rate reaching a peak at mysis 3 and declining at postlarva 1. When protozoea 1 and protozoea 2 were given Tetraselmis sp. at levels equal to or above their respective ILL's, rate of development to protozoea 3 was enhanced. Growth rate, in terms of total length, was significantly enhanced in protozoea 3 and mysis 1 if earlier stages were given Tetraselmis sp. at levels equal to or above their respective ILL's.

The effects of feeding frequency and amount of food on the growth of juvenile groupers (Epinephelus malabaricus) were investigated for 12 weeks of rearing in net-cages set in an earthen pond. The juveniles (110-130 g in body weight, BW) attained marketable size (500 g) in 12 weeks. Feeding to satiation levels once a day gave the best growth (mean BW = 509.4 ± 56.5 g) and relatively good food conversion ratio (4.78) compared to the other treatments (twice a day, once in two days and once in every three days). Concerning feeding levels, in which feed was given twice a day at 15, 10, 5 and 1% of total fish biomass per day, the best fish growth (426.6 ± 54.0 g) and a reasonable food conversion ratio (4.53) were obtained at 5% fish biomass. There was a positive correlation between the growth of fish and water temperature in both experiments.

The induction of sequential spawnings of mature female sea bass following intraperitoneal implantation of various doses of luteinizing hormone-releasing hormone analogue (LHRHa) in a 95% cholesterol pellet was investigated. LHRHa stimulated a dose-dependent increase in spawning rate (number of spawnings per fish over a 4-day period) at doses ranging from 4.75 to 75 μg/kg body weight. Higher doses ranging from 150 to 300 μg/kg resulted in significantly fewer spawnings (62.5%–75%). Untreated control sea bass did not spawn. Sham-implanted fish failed to spawn or did so at significantly lower rates (0%–6.3%) compared to hormone-treated fish. Spawning induction at the highest hormone dose tested (300 μg/kg) resulted in the lowest mean egg fertilization rate of 30.1%. Mean fertilization rates, ranging from 60.5% to 82.2%, at the lower doses of LHRHa were not significantly different. Mean hatching rates ranging from 30% to 76.5% following induction of sequential spawning by several doses of LHRHa were similar. At all hormone doses tested, mean egg production levels of 37.3–58.7×10⁴ eggs/kg body weight were highest on the first day of spawning and declined significantly on subsequent days. Mean egg production levels of 1.2–6.9×10⁴ eggs/kg were always lowest on the last day of spawning. Similar egg production levels among all hormone doses during each spawning day were observed. These results indicate that the quality and quantity of spawned eggs may, in part, be influenced by sequential spawnings triggered by LHRHa pellet implantation in sea bass.