A feeding experiment was conducted to determine the quantitative dietary requirement of milkfish juveniles for lysine. Milkfish (Chanoschanos Forsskal) of mean weight 5.92±0.14 g were fed diets containing 7.0, 11.0, 15.0, 19.0, 23.0 and 27.0 g lysine/kg dry diet for 12 weeks. The amino acid test diets contained white fish meal and zein supplemented with crystalline amino acids to provide an amino acid profile similar to milkfish proteins except for lysine. Each of the six diets was fed to four replicate groups of 25 fish in a completely randomized design and at a feeding rate of 5% of the fish body weight per day. On the basis of the growth response, lysinerequirement of juvenile milkfish was found to be 20 g/kg diet. This value corresponds to 4.0% when expressed as a percentage of the dietary protein. Survival (94–97%) was consistently high in all treatments. Except for loss of appetite resulting in low food intake and depressed growth, no nutritional deficiency signs were observed in fish given the lysine-deficient diets.

Milkfish grown on two natural foods were examined to determine the distribution pattern of the digestive lipases along the digestive tract and to identify the optimum condition for lipase activity. One food consisted of a biological complex of unicellular algae and diatoms (Food A) and the other consisted of fibrous filamentous green algae, predominantly Chaetomorpha brachygona (Food B). The major sites of lipase secretion in milkfish digestive tract were the intestines, pancreas and pyloric caeca. Lipase activity was somewhat higher for fish grown on Food A than those grown on Food B. Intestinal lipase activity was observed to be maximal at 45°C and at pH 6.8 and 8.0. Activity of pancreatic lipase was observed to be maximal at 50°C and at pH 6.4 and 8.6. The detection of two well-defined pH optima, one at slightly acidic and the other at alkaline pH for both the intestinal and pancreatic lipases suggests a physiological versatility for lipid digestion in milkfish.

This study was conducted to assess the effect of different levels of dietary intake and feeding frequencies on growth and survival of bigheadcarp, Aristichthys nobilis, fry. The feeding rates consisted of 10%, 20%, and 30% of body weight while feeding frequencies were one, three, and five times daily. Results showed that final weight, final length, and specific growth rate (SGR) differed in relation to feeding rate but not to feeding frequency. Highest values were obtained for fish on the 30% ration and fed once a day. A significant effect of higher feeding rate using lower feeding frequency on growth was manifested in final mean weight and SGR; increasing feeding rate resulted in increased growth. Feeding frequency significantly influenced fry survival with highest values observed when fry were fed once or three times per day. Highest survivals were achieved by fry on the 30% ration fed once daily. At higher feeding rates using lesser feeding frequencies better survival was noted. Survival rate had an inverse relationship to feeding frequency, but no overall relationship existed between feeding rate and survival rate. Both ration and feeding frequency significantly influenced normalized biomass index (NBI). Highest values were again obtained on the 30% ration and feeding once daily. Higher NBI values were observed with higher feeding rates at lower feeding frequencies. Increasing ration resulted in a corresponding increase in NBI.

Hormone-induction of spawning in bighead carp Aristichthys nobilis Rich. by single or double intraperitoneal injection with varying combined dosages of HCG and LHRH-A was conducted. Fish were spawned successfully following a single or double injection with 1800 to 2000 IU HCG in combination with 10, 15 or 20 µg HRLR-A per kg body weight. Fish injected with lower dosages of HGC at 1200 or 1500 IU/kg body weight plus 20 µg/kg LHRH-A did not differ significantly (P>0.05). Fish given a single injection ovulated after 12.0 ± 0.1 hours. No significant difference was found in the total number of eggs spawned per fish among the injection protocols (P>0.05). However, lower fertilization and hatching rates of eggs were observed in fish that spawned spontaneously in the tank as compared to those fish whose eggs were stripped and dry-fertilized (P<0.05).

Growth studies were conducted with milkfish (Chanos chanos Forsskal) juveniles to determine the quantitative requirements for arginine and threonine. The amino-acid test diets (40% crude protein) contained casein and gelatin supplemented with crystalline L-amino acids to provide an amino-acid profile similar to milkfish protein except for the test amino acid. Each set of experimental diets consisted of six isonitrogenous and isocaloric diets containing graded levels of the essential amino acid to be tested. Break-points in the growth curves which represent the optimum dietary concentration of arginine and threonine for fish growth were determined by the broken-line regression method. Based on dry diet, the requirement of milkfish juveniles for arginine is 2.10% and for threonine, 1.80%. These values correspond to 5.25% arginine and 4.50% threonine when expressed as a percentage of dietary protein.

Natural food in combination with either SEAFDEC formulated or other commercial larvae diets was tested for large scale production of Penaeus monodon postlarvae. Two trials of 3 treatments each, 2 replications of each treatment, were conducted in 10 m3 circular concrete tanks. Shrimps were reared from nauplii to postlarvae. Dietary treatments for trial I included:(a) natural food (NF) alone, (b) NF+ commercial plankton substitute (PS) and (c) NF+ SEAFDEC diet (SD).For trial II, commercial powder diets SP or SMP were added:(a) NF + SP, (b) NF + PS + SP + SMP and (c) NF + SD + SP + SMP. Larvae survival was significantly higher in treatments containing the SEAFDEC diets than in the treatments receiving natural food alone (trial I) or natural food in combination with SP (trial II). Larval development was faster in the group fed the SEAFDEC diet; larvae in these groups metamorphosed into postlarvae an average of 1-2 days earlier than groups fed other diets. The presence of either SP or SMP did not improve the efficiency of the feeds. Results showed that larvae performance was affected by the nutrient composition of the diets and that by using proper feeding techniques and management of water quality, large scale hatchery production of P. monodon using natural food in combination with the SEAFDEC diet or plankton substitute is possible.

Potassium permanganate (KMnO₄) is a strong oxidizing agent and is commonly used in aquatic systems to improve available oxygen, treat infectious diseases and parasites, detoxify fish poisons, and control algae. The following study was undertaken to determine the 24- and 96-h median lethal concentration (LC50) of milk fish (Chanos chanos)) fingerlings to KMnO₄. The study was also designed to evaluate the histopathological response of fish tissues to KMnO₄ but was reported in another paper (Cruz and Tamse 1986).

Samples from Penaeus monodon hatcheries (2-3 day old larvae or Zoea 1 to 34 day old post larvae or PL₃₄) and ponds (15 to 159 days old in the pond) were histologically examined for the presence of eosinophilic occlusion bodies in hypertrophied nuclei of the hepatopancreas which is indicative of P. monodon baculovirus infection. The earliest stage found infected in the hatcheries was PL₃. Infected shrimp from ponds had slow growth rates and generally pale yellow to reddish brown hepatopancreata. The infection was also characterized by the necrosis and degeneration of the hepatopancreatic tubules with secondary bacterial invasion.

The National Bangus (Milkfish) Breeding Program of the Philippines, which was launched by the Philippine government in 1981, had succeeded in spawning milkfish in captivity and in rearing the eggs to fry that were stockable in ponds. The physical productivity and economic viability of an integrated milkfish broodstock and hatchery as a public enterprise is analyzed, using SEAFDEC research findings as bases for analysis. Discounted cash flow computations show the repayment schedule for investments in structures and equipment, and operations and maintenance expenses for both broodstock and hatchery operations covering a period of 15 years. Revenues came from the sales of fry. The analysis was based on an annual stocking of 100 milkfish (200–250 g/piece) per cage with a diameter of 10 m. Egg production started during the fifth year. Investment in the hatchery facilities started during the fourth year and expansion occurred in the subsequent years to accommodate the eggs produced for rearing to the fry stage. Economic indicators, net present value (NPV) and internal rate of return (IRR), showed negative figures. The trend, however, was upward, starting during the sixth year of operation. Sensitivity analysis was done to determine the effects of changes in operational efficiencies, such as survival rates and stocking densities to the return on investment (ROI) in private hatcheries.

A qualitative and quantitative study of the ovarian maturation stages of wild-caught Penaeus monodon was conducted to refine the existing method of staging. For industrial purpose, measuring the ovarian width at the first abdominal region can minimize arbitrariness in staging. A width of 20 mm indicates readiness for spawning while reproductive performance is improved when ovarian width is 30 mm or more. Based on histology, the usual 6 to 8 stages of development can be reduced to four stages: previtellogenic, vitellogenic, cortical rod, and spent. The previtellogenic stage (P) is characterized by the predominance of oogonia and primary oocytes in the chromatin nucleolus and/or perinucleolus stage. The vitellogenic stage (V) is marked by the presence of yolky oocytes. The cortical rod stage (C) is distinguished by the appearance of yolky oocytes with spherical or rod-like bodies at the peripheral cytoplasm. The spent stage (S) can be distinguished by the presence of few oocytes with yolky substance and/or cortical rods, thicker layers of follicle cells, and few darkly-stained, irregularly shaped primary oocytes. Individuals classified as stages II+ and III+ showed similarity in size and shape of all lobes in the posterior thoracic region, and histologically, corresponded to the revised stages V and C, respectively. Histochemical staining shows that glycoproteins and lipids are absent in the primary oocytes and present in yolky oocytes. Glycoproteins but not lipids occur in the cortical rods. Analysis of variance showed significant differences in mean gonad weight and gonadosomatic index values but not in the mean body length and body weight values in stages P to C. Uniformity in the number, stage and composition of oocytes in the four regions of the ovary at each stage showed that stage of ovarian maturity in wildprawns can be represented by any region of the ovary. Differences in the oocyte size frequency and mean values of average and maximum oocyte diameter in the four stages showed that these are good indicators of stage of maturation in wild P. monodon.