The hepatocytes of seaperch fingerlings reared on trashfish at constant water temperatures of 20 and 35°C were examined through electron microscopy and compared with those of controls fed identical diet or deprived of food at fluctuating temperatures 26.5-30°C to determine whether temperature alters subcellular liver morphology. While cytoplasmic compartmentation of the hepatocytes was not evident in both the fed and starved controls, a well-developed compartmentation characterized the hepatocytes of both fishes acclimated for 7 and 14 days at 20 and 35°C. Exposure of the fish at these temperatures also induced an initial reduction of lipids followed by changes in their electron densities, whereby lipids at 35°C were less osmiophilic than at 20°C and 26.5-35.0°C. Except for a slight variation in glycogen, no major modifications occurred in terms of lipid number and electron density in the fed controls, whereas in the starved controls, progressive decline of lipids coupled with increasing electron densities of the remaining lipids were observed over the 14-day experimental period. The need for studying temperature effects on tropical species is discussed.

The efficacy of the silo and broadcast methods of applying organic fertilizers in ponds for the production of pond-floor, microbenthic biological complex, a natural food source known as lablab, was tested in 1-ha ponds, replicated thrice in time. Although there were no statistically significant differences (P > 0.05) in milkfish growth, survival and production between the two treatments tested, after 90 days production tended to be higher in ponds prepared with the silo method. Advantages of the silo method are that it is less laborious, cheaper, and less time consuming than the broadcast method and results in consistent lablab growth until the end of the culture period.

The effect of various doses of luteinizing hormone-releasing hormone analogue (LHRHa) ranging from 1 to 100 μg/kg body weight on the spawning response of mature female sea bass, Lates calcarifer (Bloch) was tested. A single intramuscular injection of LHRHa resulted in a dose-related increase in the spawning rate (number of spawnings of each fish over four consecutive days) of mature fish. An LHRHa dose of 5 μg/kg and less induced low spawning rates of 16.7% to 37.5% or at least one spawning every four days. However, mature sea bass spawned more than once (43.8–58.3%) in four days at dose levels of 10 μg/kg and above. Hormone treatment within the dose range tested did not influence the number, fertilization and hatching rates of spawned eggs. The influence of initial oocyte size on the LHRHa-induced spawning response of mature sea bass was also examined. Sea bass with an initial oocyte diameter of 0.30–0.39 mm did not respond to the single injection of 100 μg LHRHa/kg. In contrast, LHRHa induced spawning among sea bass with an initial egg size of 0.40–0.49 mm, although two of four sea bass of the same stage of ovarian maturity spawned spontaneously. Fish having an initial oocyte size of 0.50–0.55 mm spawned with and without LHRHa treatment. Spontaneous spawning among saline-injected sea bass occurred at a later time (24–58 h post-injection) compared to fish induced to spawn by a single injection of LHRHa (8–36 h post-injection). The initial spawning response time interval for fish with an initial egg size of 0.50 mm or greater was further reduced to 8–9 h by LHRHa. These results indicate that LHRHa can successfully induce spawning in mature female sea bass which have attained a critical oocyte diameter and that the spawning response interval is reduced with a further increase in egg size beyond the critical oocyte diameter limit.

A collecting gear for naturally-spawned milkfish (Chanos chanos Forsskal) eggs in circular floating net cages is described. The gear has been shown to be effective in collecting large numbers of eggs. The collecting gear can be adopted for other broodstock fish species held in circular floating net cages.

The gonadosomatic index (GSI) and the hepatosomatic index (HSI) were determined for wild-caught, eyestalk ablated Penaeus monodon at 5 reproductive stages (I to V). Tissues of the muscle, ovary and hepatopancreas in each stage were analyzed for crude protein and amino acid composition. Results showed that the GSI increased from stage I (immature) to IV (fully mature) but declined at stage V (spent) while the HSI did not change significantly (P less than or equal to 0.05). Muscle protein content did not vary markedly from stage I to V except for a slight lowering at stage III (late maturing). Ovarian protein increased from stage I to IV and decreased at stage V while from stage II, the reverse was true for hepatopancreas. Generally, few significant differences in amino acid content were found. Glutamic acid content significantly differed among stages in all three tissues. In addition, phenylalanine in the muscle, histidine and lysine in the ovary and arginine and luecine in the hepatopancreas differed among stages. The muscle had slightly higher arginine and gluatmic acid contents than the ovary and hepatopancreas but was lower in threonine and valine. The ovary had the lowest glycine content. Results showed similar amino acid levels among tissues and maturation stages, suggesting that amino acids are fixed and not affected by much variation.

The effects of different types of feed, given singly or in combination, on the growth and survival of bighead carp, Arislichlhys nobilis Richardson, larvae reared for a period of 12 weeks were determined. Growth was highest for fish fed with the combination of Moina and artificial feed followed by fish fed with artificial feed alone. Significantly lower (P < 0.05) growth was found in fish fed with green water +Moina+ artificial feed; green water + artificial feed; green water +Moina and Moina alone, in a descending order. Carp larvae reared in green water alone did not survive after the fifth day of feeding. Specific growth rales ranging from 0.59% day−1 to 2.75% day−1 were exhibited by fish in all the remaining six treatments. Although green water alone did not support the growth of the larvae, enhanced survival rates were observed when green water was given in combination with other feeds. Survival rate was highest in fish fed with the combination of green water, Moina and artificial feed, but was not significantly different (P > 0.01) from those given Moina+ artificial feed. Consequently, normalized biomass index was significantly high (P < 0.05) in fish fed with the combination of green water, Moina and artificial feed.

Asian seabass (Lates calcarifer) larvae were fed Brachionus cultured on Chlorella and, as soon as ingestin was possible, different types of Artemia, i.e., nauplii of the San Francisco Bay (SFB) strain, Great Salt Lake (GSL) strain or GSL nauplii that had been bioencapsulated with an emulsion containing high levels of the ω3-HUFAs (highly unsaturated fatty acids) 20:5 and 22:6. San Francisco Bay Artemia with a good natural fatty acid profile and small body size could be offered earlier than the larger but HUFA-poor Great Salt Lake strain. The poor nutritional quality of the latter, however, could be corrected by enriching the nauplii with an ω3-HUFA emulsion for 24 h, after which time high levels of the ω3-HUFAs 20:5 and 22:6 were obtained. When the Artemia diet offered before metamorphosis included natural or supplemented essential fatty acids, no significant differences in dry weight, length or survival of the fish were noticed, as compared to fish fed the naturally deficient GSL Artemia. Onset of metamorphosis and physiological condition after metamorphosis, however, were influenced by the HUFA content of the ingested prey. Seabass larvae fed SFB or enriched GSL Artemia started metamorphosis on day 19, while those in the non-enriched series never achieved metamorphosis and died of a nutritional deficiency syndrome by day 27. An indication of the physiological condition of the larvae and the early detection of the syndrome was possible by subjecting 21- and 25-day-old larvae to a stress test: abrupt exposure of the larvae to 65-ppt saline water resulted in abundant and early mortality in HUFA-deficient fish larvae. Fry receiving ω3-HUFA-fortified Artemia had a superior physiological condition which was reflected by significantly lower mortality figures in the stress test.

The effects of 24-h lighting on feeding, growth and survival of first-feeding larvae of Siganus guttatus were tested. Continuous light gave a higher mean survival (31.69%) with a maximum of 40.50% compared to natural daylight (17.10%). Larval size on day 7 also showed that continuous lighting gave improved results. Although feeding incidence increased with age of the larvae, a higher incident rate was observed for larvae held in continuous light from day 3.

The effect of storage temperature was evaluated on the basis of growth response of prawns fed for 10 weeks with diets stored at 0°C, 10°C, 28°C-31°C (ambient temperatures) and 40°C for a period of 10 weeks. Prawns were stocked at 15 pieces per 60-1 oval thank supplied with water at 28°C and 32 ppt in a flow-trough aerated system.There were five replicate tanks per treatment. Lowest weight gain (20 g) was observed for prawns fed the diet stored at 40°C and significantly higher growth response was observed as the storage temperature decreased (30.2g at 28-31°C; 37.7g at 0°C and 10°C). Body size was significantly (P<0.05) affected by diet after 6 weeks of feeding and highly significantly (P<0.01) after 8 weeks of culture.Peroxide values for diets exposed for 10 weeks to 28°-31°C (2.9 meq/kg). The highest survival rate (76%) and feed conversion (8.9%) were observed for prawns fed diets stored at low temperatures (0° or 10°C). Severe necrosis of the hepatopancreatic cells was observed in P. monodon fed with diet stored at the high temperature.

Monthly samples of sediment, water and commercially important species of fish, primarily Oreochromis niloticus and Chanos chanos , plus a few other species, were collected from the West Bay area of Laguna Lake, The Philippines from January to December 1987. Mercury levels were determined in all samples by cold vapor atomic absorption spectrophotometry. Results showed that sediment samples contained mercury levels ranging from 26.7 to 117 ppb. Mercury levels in water samples were low, ranging from below detectable to 0.5670 ppb. The mercury levels in the water were negatively correlated with conductivity and dissolved oxygen and positively correlated with turbidity. The mercury burden of the fish species samples was below the maximum permissible level set by the WHO and USFDA of 0.05 ppm. No direct correlation was observed between mercury levels in sediment and water, water and fish and sediment and fish.