The seasonal abundance of milkfish fry in the Philippines has led to the practice of buying a sufficient supply during the peak season to compensate for the shortage during slack periods. Fry that are not immediately grown out are crowded and stunted in transition ponds until they are transferred to rearing ponds. Milkfish farmers believe that stunted fingerlings grow faster than newly grown ones and therefore yield extra croppings. To assess the efficiency of production schemes, stunted and non-stunted milkfish fingerlings were cultured in twelve 144-m² ponds for a 3-month period. The treatments employed were: Treatment I, 2-month-old fingerlings; Treatment II, 3-month-old fingerlings; and Treatment III, 6-month-old fingerlings, with the initial weights of 3.3 g, 7.8 g, and 43.1 g, respectively. Survival, netproduction, cumulative and monthly weight gains did not differ significantly (P > 0.05) among the three treatments. The results indicate that stunting did not illicit a significant increase, nor did it adversely affect the growth, survival, and netproduction of milkfish in a straight culture system. Stunting can therefore be practised by farmers to provide an adequate supply of fingerlings for year-round operation.

Feeding trials were conducted to determine the effects of linoleic acids on growth, survival, fatty acid composition and liver histology of milkfish. Five isocaloric semi-purified diets were formulated, either lipid-free or containing the following lipids: 7% lauric acid (LA), 6% LA + 1% linoleic, 6% LA + 1% linolenic acid, and 6% LA + 0.5% linoleic + 0.05% linolenic acids, and fed to milkfish with an average weight of 1.55 ± 0.25 g. there were no significant differences in growth or survival between fish fed the lipid-free and the LA diets in the five treatments tested. However, growth of fish fed with linoleic and linolenic acids was significantly higher (P<0.05) than that obtained in fish fed lipid-free and LA diets. The best growth response (233%) was attained with fish fed linolenic acid alone. Fatty acid analyses of the total lipid showed that lipid-free and LA diets increased the levels of monoenoic acids in the fish. The addition of linoleic and linolenic acids, alone or in combination, suppressed the levels of these monoenes and increased the levels of polyunsaturated fatty acids (PUFA). Histological analyses using light microscopy revealed slight abnormalities in the hepatocytes of fish fed lipid-free and LA diets. Both linoleic and linolenic acids are effective for good growth and survival of fingerling milkfish; however, the effect of linolenic acid on the growth of this species is better than that of linoleic acid.

The study was conducted in twelve 144-m² ponds to evaluate the effect of different organic and inorganic fertilizers on the growth, survival, gross production, and profitability of marketable milkfish. The following treatments were used: Treatment I, SEAFDEC traditional fertilization practice (16-20-0 at 50 kg/ha and 45-0-0 at 15 kg/ha); Treatment II, half-dosage of Treatment I; Treatment III, chicken manure at 0.5 ton/ha; and Treatment IV, MASA (processed from agricultural and industrial wastes) fertilizer at 0.5 ton/ha. All treatments were applied once in every 2 weeks. No significant difference (P > 0.05) existed in the harvest and production of milkfish among the treatments. However, economic indicators such as return-on-investment (ROI), payback period, and marginal analysis ranked the performance of the fertilizer treatments in the order of I, II, III and IV. Fish kills occurred in three ponds applied with chicken manure and MASA fertilizer. This could have been due to a heavy build-up of organic matter in the pond bottom which led to the collapse of the benthic algal community, depletion of dissolved oxygen and the presence of hydrogen sulfide. It is therefore suggested that a lower dosage of organic fertilizer should be applied in ponds especially during the rainy season.

The study was undertaken to determine the optimum combination of the frequency of water replenishment and fertilization that can yield the highest growth, survival, and gross production of milkfish. Results indicated that mean body weight and survival were not significantly different (P > 0.05) among the treatments. Gross fish production was higher in biweekly fertilization if considered as a single factor. However, when this was in combination with the weekly or biweekly water replenishment, similar gross fish production was attained. In any case, because biweekly fertilization has a better effect than a weekly schedule, the former should be used in combination with any other level of replenishment. A weekly water replenishment, however, is impractical in big pond areas of 5–10 ha compartments which are still common in some milkfish ponds in the Philippines. Therefore, biweekly water replenishment and fertilization with 16–20–0 at 50 kg ha^-1 would be reasonable.

The performance of an artificial practical diet, kappa-carrageenan microbound diet (C-MBD) was assessed on Penaeus monodon larvae at the SEAFDEC Broodstock and Maturation Experimental Laboratory in March 1986. Shrimps were reared from zoea to post-larvae using five dietary treatments: (a) natural food - Chaetoceros calicitrans and Artemia salina ; (b) C-MBD; (c) combination of natural food and C-MBD; (d) commercial diet (microencapsulated, MED); (e) combination of natural food and commercial diet. Results showed slow development with larvae fed the commercial diet. Feeding with C-MBD in combination with natural food resulted in the highest % survival among treatments (69.6), but this was not significantly different (p > 0.05) from those obtained with larvae fed natural food alone, C-MBD alone or their combination.

Oreochromis niloticus fingerlings were stocked at three different initial size ranges of 1-3, 7-12 and 20-30 g in fixed net cages in Laguna Lake, Philippines. These were reared without supplemental feed for 120 days. Fingerlings with the biggest initial size at stocking were the most efficient in terms of average weight gain, average final fish weight and total fish production.

The effect of loading density, transport duration, water temperature, and salinity on survival of young rabbitfish (Siganus guttatus Bloch) under simulated transport conditions was investigated. The rocking motion of transport was simulated by an electric shaker. At ambient temperature and salinity (28°C/32‰S) increasing loadin density and transport duration resulted in decreasin fish survival rates. When both temperature ant salinity (20°C/20‰S) were lowered survival improved sinificantly. Dissolved oxygen, water temperature, and salinity were critical factors affecting survivaf of young rabbitfish during simulated transport. Based on the results, a density of 100 fish/L can be packed for 8 hours of transport and 300 fish/L for 2 hours at 28°C and 32‰, and about 200 fish/L for 4 hours at 20°C and 20‰S.

Mudcrabs, Scylla serrata Forsskal, were monocultured at different stocking densities: 5000, 10 000, 15 000 and 20 000/ha for 90 days. Highest mean weight, survival and relative growth increment (P>0.05) were obtained from a stocking density of 5000/ha. Best feed conversion ratio of 1.72 and corresponding gross production of 1019 kg/ha per crop were attained at the same stocking density. The economic indicators, i.e., return on investment and return on equity, were also highest at 5000/ha stocking density and the payback period was shortest. Partial budgeting showed that no incremental benefit accrued from stocking beyond 5000/ha. Sensitivity analysis showed that even if the value of mudcrab were to decrease by 28%, mudcrab monoculture would still be economically viable.

P. monodon juveniles with an initial mean weight of 0.62 g were fed isonitrogenous (45%) and isolipidic (10%) semi-purified diets containing 10, 20 and 30% trehalose, sucrose and glucose for 56 days. Shrimp fed the diet with 20% trehalose had the highest weight gain. Of the three types of sugar tested, shrimp fed diets containing trehalose and sucrose exhibited better weight gains than those fed glucose diets. A dietary sugar level of 20% resulted in the best weight gain whereas the 30% level gave the lowest weight gain. The survival of shrimp was also affected by the type of carbohydrate fed. Trehalose and sucrose diets promoted higher survival rates than glucose diets. The different types and levels of carbohydrates showed combined effects on the dry matter percentages of crude protein and total lipid. Trehalose and sucrose diets generally promoted increased protein deposition. Trehalose at 30% and sucrose at 20% depressed lipid content.

Penaeus monodon postlarvae were fed with formulated diets containing either soaked or unsoaked Leucaena leaves. A similarly prepared feed with soybean in place of Leucaena was used for comparison. Results were analysed by statistical and histological methods. Results of the 4-week feeding experiment showed that mean weight gains and percentage survival of the prawns fed with the two Leucaena-containing diets were higher, but not significantly different from soybean-containing diet. The content of the poisonous amino acid mimosine in the Leucaena leaves could be reduced about 70% by soaking the leaves in freshwater for 24 h. Highest weight gain was obtained with the feed containing these soaked leaves. In addition to growth and survival, the R-cells of the midgut glands of the postlarvae were investigated by light and electron microscopy. Although the statistical growth values and the proximate analyses of the test diets were similar, a food-specific ultrastructure was established after only 4 days of feeding. All diets resulted in subcellular characteristics typical for well fed prawns and, at that time, the Leucaena diets were already slightly superior to the soybean control. This indicates that different sources of macronutrients lead to different ultrastructures even if the proximate analyses of protein, carbohydrate and lipid are similar. Only slight changes in the R-cells were observed after 11, 20 and 28 days in the prawns fed with the soybean diet compared to 4 days of feeding. In the diet containing unsoaked Leucaena leaves, however, many R-cells became heavily damaged after 20 and 28 days, whereas the prawns fed with the diet containing soaked leaves exhibited less pronounced distortion. Statistical analyses of growth and survival rate did not show these adverse effects at that time. Although it is highly probable that the mimosine is responsible for those pathological symptoms, complementary experiments could not clearly prove that. The effects of feed components are visible on the cellular or organ level after only a few days, whereas the individuals (organism level) reflect them about 10 days later. Another 10 days later the changes are manifested in the population. Therefore it is suggested to use histology in nutrition studies as a supplementary source of information to statistical and biochemical parameters. The midgut glands can further be used to monitor the nutritional condition of prawns in aquaculture, sea ranching, and in ecological investigations. The study confirms that Leucaena leaves are a promising protein source for prawn diets if mimosine could be reduced to a very low level. A mimosine level of 0.25% in the feed is still too high, if the diet is used uninterruptedly for several weeks.