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.

The influence of various levels of kinetin on growth, carbohydrate, nitrogen, and protein content of Azolla pinnata var. imbricata plants cultured in a nitrogen-free 40% Hoagland’s solution under greenhouse conditions was investigated. Kinetin concentration of 0.10, 1.0 and 5.0 ppm significantly enhanced fresh matter yield during a two week period. The carbohydrate content increased in plants subjected to 0.10 and 1.0 ppm kinetin. The significant increase in the nitrogen and protein levels of whole plants grown in the presence of 0.01, 1.0 ppm kinetin would enhance its nutritive quality as fish feed. Kinetin at 10 ppm decreased yield as well as carbohydrate, nitrogen and protein content.

The effects of dietary leucaena leaf meal on reproductive performance and growth of Nile tilapia were determined. In the preliminary trial, sexually mature Nile tilapia were fed with a control diet or a test diet which had leucaena leaf meal as the only protein source for 24 weeks. Fish fed with the leucaena diet lost some weight and had significantly low (P<0.05) gonadosomatic index and fry production compared to those fed with the control diet. Subsequently, four isonitrogenous diets (20% crude protein) containing varying amounts of leucaena leaf meal (0, 20, 40 and 80%) were fed to Nile tilapia broodstock. Mean weight gain of the female fish decreased as the level of leucaena leaf meal in the diets increased. Females fed with the 80% leucaena diet invariably lost weight. Mean weight gain of males fed with the control diet and the 20 and 40% leucaena diets did not differ significantly (P>0.05). However, growth of males fed with the 80% leucaena diet was remarkably low. Fry production was highest for those fed with the control diet and the 20% leucaena diet. Fry production decreased slightly in fish fed with the 40% leucaena diet and was significantly low (P<0.05) for those fed with the 80% leucaena diet. The low fry production was preceded by a decrease in body weight of the female fish. However, the gonadosomatic indices of the females and the males were not markedly affected by the diets. On the basis of both fry production and growth, leucaena leaf meal should not exceed 40% of the diet of Nile tilapia broodstock.

The nutritional value of Artemia sp. as food for marine fish and crustacean larvae has been linked to the level of its polyunsaturated fatty acid (PUFA) content. Experiments in August 1984 were conducted to determine the effects of various artificial diets and algae on fatty acid composition of PUFA-deficient Artemia sp. (Utah GSL strain) and their resulting value as food for postlarvae of the prawn Penaeus monodon (Fabricius). Nauplii of the brine shrimp were grown on extracts of corn, copra, soybean and rice bran containing precursors (C18) to long-chain PUFA and also on algal species containing different levels of long-chain PUFA (C20). The nauplii were then used as food for P. monodon postlarvae. The results revealed that absence of C20 polyunsaturates from the feeds and their presence in the algae were reflected in the polyunsaturated fatty acid content of the tissues of Artemia sp. When fed with brine shrimp fed on algae, P. monodon displayed better postlarval survival and significantly higher growth; related to the content of polyunsaturated fatty acids in Artemia sp. A practical feeding approach in prawn hatcheries would be to grow Artemia sp. on a cheap diet such as rice bran, and then to enhance its nutritional value with a diet high in PUFA prior to harvesting, in order to improve hatchery production.

Nine experiments were conducted to investigate the influence of chronic administration of testosterone (T) and gonadotropin-releasing hormone (GnRH) analogues on first maturation of 4- to 6-year-old fish and rematuration of 6- to over 9-year-old spent/regressed fish. Implantation of T or T in combination with luteinizing hormone-releasing hormone analogue (LHRH-A) had no marked effect on maturation rate of 4-year-old milkfish. The percentage of maturing fish was low and similar to controls in Experiment 1 (T, 31–35%; control, 35%) and Experiment 3 (T, 13%; T plus LHRH-A, 28%; control, 22.2%). Most of the 4-year-old maturing fish were males; maturing females were obtained only from the T-implanted groups in Experiment 1. In Experiment 3, T-implanted maturing females were able to retain yolky eggs whereas maturing control females did not, indicating that testosterone may have enhanced vitellogenesis and maintained the integrity of vitellogenic oocytes. Tank-reared maturing 4-year-old females, about half the size of older first maturing females, were induced to spawn. This is the first case of maturation and spawning of 4-year-old milkfish reared in tanks. As in Experiments 1 and 3, the percentage maturation of spent fish in Experiments 7 and 8 was similar for T-implanted and controls. On the other hand, the 4-year-old immature fish in Experiments 2 and 4, the 5- and 6-year-old immature fish in Experiments 5 and 6, and the spent 6-year-old fish in Experiment 9 were immature or regressed throughout. The factors which may have influenced the results of these experiments include age and reproductive history of the fish, timing of hormone implantation, experimental and holding conditions, and stress.

The effects of Na-EDTA on growth and survival of Penaeus monodon larvae were determined for applications given daily or every 3 days. Application of 2.0, 5.0, and 10.0 ppm were given on day 1, day 4 and day 7 in Experiment 1, and 5.0 and 10.0 ppm were given daily for 8 days in Experiment 2. Larvae stocked at 100/liter were given a natural food diet of Chaetoceros calcitrans and Artemia salina nauplii. Chloramphenicol (2.0 ppm) and Treflan R (0.05–0.10 ppm) treatments were applied on the same days as Na-EDTA. Water change was 30% on day 4 and 50% daily thereafter. Results showed that the application of Na-EDTA at 5.0 and 10.0 ppm on days 1, 4 and 7 greatly improved the survival of P. monodon larvae. With daily application, the larvae treated with 10.0 ppm showed the best survival rate during the 8-day culture period. Na-EDTA treatments at dosages above 2.0 ppm seem to prevent significant mortality. It is believed that Na-EDTA improved survival rates by chelating toxic elements in the culture medium. Growth (rate of metamorphosis) was not greatly improved except for anuplii to zoea where the highest percent molts were observed with the 10.0 ppm treatment in both experiments.

Aeromonas hydrophila was consistently associated with necrotic ulcers and lesions in mudfish/snakehead (Ophiocephalus striatus), Thai catfish (Clarias batrachus), crucian carp (Carassius carassius) and goby (Glossogobius giurus) in Laguna de Bay, Philippines, during the months of December 1985 through February 1986. The bacterium was isolated from body lesions and ulcers of all fish examined and rarely from the kidney and liver of carp and catfish. The disease was characterized by hemorrhages, lesions and open necrotic ulcers on the body of the fish, particularly the head (just behind the eyes), the mandible and the maxilla, and the caudal peduncle regions. Erosion of the head bone tissues and the tails was observed in very severe cases. The presence of A. hydrophila is believed to be secondary to some predisposing factors existing in Laguna de Bay.