This paper reviews various aspects of the biology and effects of 2 caligid copepods, Lepeophtheirus salmonis and Caligus orientalis, on wild and farmed fish in sea and brackish waters of Japan and adjacent regions. Lepeophtheirus salmonis is a common parasite of wild adult chum (Oncorhynchus keta) and pink (O. gorbuscha) salmon migrating in northern Japanese waters. Masu salmon (O. masou) have the lowest level of infection. Juvenile chum salmon are sometimes infected. This parasite is also found on salmonids in Korean and Russian waters. The species occurs on coho salmon (O. kisutch) and rainbow trout (O. mykiss) farmed in coastal waters of northern Japan, but its infection is not a serious problem, because only young fish are reared and harvested in less than a year of culture and thus no fish are cultured during summer. This situation is very different from that in Scotland, Ireland, Norway, and Canada where L. salmonis causes serious damage to farms of Atlantic salmon (Salmo salar). Caligus orientalis is a parasite of coastal marine and brackish-water fish in Japan and neighboring countries (Taiwan, China, Korea, and Russia). This parasite has a wide host range and has been reported from over 20 fish species from different orders and families. It infects farmed and experimentally reared fish, such as rainbow trout in Japan, grey mullet (Mugil cephalus) and black porgy (Acanthopagrus schlegeli) in Taiwan, and Mozambique tilapia (Oreochromis mossambicus) in China. Heavy infection results in appetite reduction and death of fish. The parasite is one of the most important pathogens at brackish-water fish farms in Far East Asia.

Species of the economically important gracilarioid seaweeds from the Philippines were studied to determine the monthly variation in agar quality. Yield, gel strength, melting and gelling temperatures, and sulfate contents were compared. Lowest agar yield was observed in Gracilaria changii in July (4.15%) and highest in Gracilariopsis heteroclada in March (20.84%). Gel strength was lowest in G. heteroclada in November (44 g cm^-2) and highest in Gracilaria tenuistipitata in January (874 g cm^-2). Melting temperature was lowest in G. heteroclada in November (68.7°C) and highest also in G. heteroclada in January (90.3°C). Gelling temperature was lowest at 34.4°C in G. changii and Gracilaria firma in November and December, respectively; and highest in G. heteroclada in October (45°C). Sulfate content was lowest in G. firma in November (0.16%) and highest in G. heteroclada in February (2.71%). The variation in the agar parameters could be due to different composition of agars of different species. Sulfate is significantly lower in Gracilaria firma. Yield is significantly higher in Gracilariopsis heteroclada. There is no significant difference in the gel strength, melting and gelling temperatures among species.

Apparent digestibility coefficients (ADCs) for dry matter (ADC_dm) and crude protein (ADC_cp) of selected feed ingredients were determined in vivo for grouper using passive faeces collection (Guelph System). A reference diet (RF) and test diets (consisted of 70% RF and 30% test ingredient) with 1% Cr₂O₃ as an inert indicator were used. An RF contained 45% protein, 10% fat and 15.7 kJ g⁻¹ metabolizable energy. Three isonitrogenous and isocaloric diets, each contained a test ingredient (white fish meal, white cowpea meal and ipil-ipil leaf meal), were used in a growth study based on ADC_cp of feed ingredients. An RF without Cr₂O₃ was a control. The ADC values of experimental diets were also determined. In grouper, the ADC_dm of white cowpea meal, defatted soybean meal, wheat flour and shrimp meal (74–76%) were significantly lower than that of squid meal (99%), but comparable with those of the fish meals (84–89%). No significant difference was observed between the ADC_dm of ipil-ipil leaf meal, rice bran and wheat flour (56–73%). The ADC_cp of white cowpea meal and defatted soybean meal were similar to those of the fish meals, squid meal and shrimp meal (94–99%). The ADC_cp of wheat flour was comparable with that of ipil-ipil leaf meal (79–83%). Rice bran had the lowest ADC_cp value of 43%. Based on specific growth rate (SGR), the growth of fish fed white cowpea meal-based diets was similar to that of the control fish (3.2–3.3% day⁻¹). Also, no significant difference was observed between the ADC_dm (68–72%) and ADC_cp (88–91%) of white cowpea meal-based diet and the control diet. The results suggest that ADC values can be used as indicators to determine the nutritional value of feed ingredients. White cowpea meal can be incorporated as a protein source in practical diet for grouper at 20.5% of the diet with no adverse effect on growth.

Viral nervous necrosis (VNN), also known as viral encephalopathy and retinopathy (VER), is an emerging disease affecting larvae and juveniles of many farmed marine fish species in Asia, Australia, Europe and North America. Mass mortality occurred in 14-day old larval sea bass Lates calcarifer at a hatchery in the Philippines associated with clinical signs such as abnormal swimming behavior and pale-gray discoloration of the body. Histological investigations in moribund fish revealed marked vacuolation in the retina and brain. Cytopathic effects (CPE) were observed in SSN-1 cells inoculated with the tissue filtrate of affected sea bass. A piscine nodavirus, the causative agent of VNN, was detected in the affected tissues and SSN-1 cells inoculated with the tissue filtrate of affected fish by RT-PCR. Electron microscopy revealed non-enveloped viral particles, 22-28 nm in diameter, in the cytoplasm of the brain and retina of affected fish and in the cytoplasm of VNN-infected SSN-1 cells after CPE appeared. These results indicate that mass mortality of sea bass larvae in the Philippines was caused by a piscine nodavirus.

Outbreaks of heavy infestation by the parasitic dinoflagellate Amyloodinium ocellatum in hatchery-reared milkfish (Chanos chanos) and mangrove red snapper (Lutjanus argentimaculatus) caused 100% mortality events in hatcheries in the Philippines. Parasites were recorded on the body surface in 14-day-old milkfish fry and on both skin and gills in 2-month-old snapper. Trophonts of A. ocellatum caused local erosions of fish skin and degeneration of epithelial cells at the sites of the parasite's attachment to the body surface. Separation and hyperplasia of gill epithelium and fusion of secondary lamellae at the distal parts of the gill filaments were common. High pathogenicity of A. ocellatum to fish may be attributed to the severe alterations of the fish gills, the disruption of the host's skin, and feeding of trophonts on hosts' epithelial cells. In-vivo treatments of A. ocellatum-infested snapper with a 1 h freshwater bath and 200 ppm H₂O₂ showed promising results. This is the first report of A. ocellatum infestation in milkfish and mangrove red snapper in the Philippines.

This study was conducted to evaluate the effect on growth and feed efficiencies of the mangrove red snapper (Lutjanus argentimaculatus) when dietary fishmeal is partially replaced by defatted soybean meal (DSM). In the preliminary experiment, snapper (mean weight±SD, 58.22±5.28 g) were fed in triplicate with different dietary amounts of DSM (7.8–42.2%) that were formulated to be isonitrogenous and isocaloric. After 14 weeks, survival, growth and feed efficiencies, and hepatosomatic index (HSI) did not differ. Based on these results, a feeding trial was done using a positive control diet that contained 64% fishmeal, while the other four diets had DSM levels of 12%, 24%, 36%, and 48% that replaced fishmeal protein at 12.5%, 25%, 37.5%, and 50% respectively. All diets were formulated to have about the same protein level (50%), protein to energy ratio (P/E of 25-mg protein kJ⁻¹), and dietary energy (19.8 MJ kg⁻¹). These were fed to triplicate groups of snapper (mean total weight tank⁻¹±SD, 73.19±1.2 g) at 15 fish (average weight, 4.88 g) per 1.5-t tank for 19 weeks. Growth (final average weight and specific growth rate (SGR), feed conversion ratio (FCR), survival, and HSI were not significantly different (P>0.05) while protein efficiency ratios or PERs were similar in treatments with DSM. Among snapper fed DSM, haematocrit value was significantly lower in fish fed 48% DSM and not different with fish fed 36% DSM. Whole-body crude fat of snapper fed 48% DSM was lowest while the crude protein and nitrogen-free extract (NFE) levels were highest. Histopathological analysis showed that lipid vacuoles in livers of snapper were reduced in size as dietary DSM increased. There was slight lipid deposition in the liver of snapper at 36% DSM while at 48% DSM it was excessive and hepatocytes were necrotic. There were no differences in the histology of snapper intestine. Under the experimental condition of this study, DSM can be used in snapper diets at 24% (replacing 25% of fishmeal protein) based on growth, survival and feed efficiencies, and histology of liver and intestine. For a lesser diet cost, an inclusion level higher than 24% DSM is possible with a bioavailable phosphorus supplement.

The effects of orally administered carotenoids from natural sources on the non-specific defense mechanisms of rainbow trout were evaluated in a nine-week feeding trial. Fish were fed four diets containing either β-carotene or astaxanthin at 100 and 200 mg kg⁻¹ from the marine algae Dunaliella salina and red yeast Phaffia rhodozyma, respectively, and a control diet containing no supplemented carotenoids. Specific growth rate and feed:gain ratio were not affected by dietary carotenoid supplementation. Among the humoral factors, serum alternative complement activity increased significantly in all carotenoid supplemented groups when compared to the control. On the other hand, serum lysozyme activity increased in the Dunaliella> group but not in the Phaffia group, whereas plasma total immunoglobulin levels were not altered by the feeding treatments. As for the cellular responses, the superoxide anion production from the head kidney remained unchanged while the phagocytic rate and index in all supplemented groups were significantly higher than those of the control. These findings demonstrate that dietary carotenoids from both D. salina and P. rhodozyma can modulate some of the innate defense mechanisms in rainbow trout.

This study determined the holding capacity of semi-intensive and intensive milkfish ponds and water quality in relation to fish biomass and feed input. Six units of 1000 m² brackishwater ponds were used, three ponds for intensive system (20,000 fish ha⁻¹) and three for semi-intensive system (8000 fish ha⁻¹). Average production was significantly higher in intensive pond (3652 kg ha⁻¹) than in semi-intensive pond (1352 kg ha⁻¹) after a desired marketable size of fish was reached. Highest concentrations in effluents (mg l⁻¹) of rearing water measured every 2 weeks were 0.369 and 0.289 for chlorophyll a (chl a), 0.485 and 0.512 for PO₄–P, 0.279 and 0.811 for TAN, 0.094 and 0.082 for NO₂–N, and 14.040 and 8.649 for NO₃–N, 216 and 142 for total suspended solids (TSS), 15.0 and 21.7 for biological oxygen demand (BOD), in intensive and semi-intensive ponds, respectively. Lowest morning dissolved oxygen (DO) in intensive pond was 2.2 mg l⁻¹, and did not decrease further because of aeration. In unaerated, semi-intensive pond, morning DO ranged from 1.3 to 5.0 mg l⁻¹ but occasionally went below 1.0 mg l⁻¹ resulting to fish mortalities at biomass of 835, 1206, and 1489 kg ha⁻¹. Levels of NO₃–N and dissolved inorganic N are linear functions of fish biomass or feed input in all systems (P<0.05). The buildup of nutrients is more pronounced at biomass of 1610 kg ha⁻¹ and above while nutrient transformation (conversion of PO₄–P or TAN to phytoplankton or vice versa) is apparent at biomass below 1419 kg ha⁻¹. The holding capacity of unaerated, semi-intensive pond is below 1348 kg ha⁻¹ or 54 kg feed ha⁻¹ day⁻¹ based on DO concentration of less than 1.0 mg l⁻¹. However, the holding capacity can be lower than 835 kg ha⁻¹ or 33 kg feed ha⁻¹ day⁻¹ during very calm weather or during rainy days when water column is stratified. Based on the results of regression analysis, the holding capacity of intensive pond should be set below 5107 kg ha⁻¹ or 110 kg feed ha⁻¹ day⁻¹ so as not to exceed the acceptable levels for water quality variables in effluent waters.