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.

Chlorination of sand-filtered and microfiltered seawater for 24 hours significantly reduced the initial bacterial load from 10⁵ to 10⁰ - 10¹ colony forming units (cfu) per ml. The total plate counts steadily increased however, after neutralization, reaching levels similar to those of untreated water 24 hours later. Results suggest that chlorine exerts bacteriostatic effects at 5 to 30 ppm and that water should be used within 6 hours after neutralization when the bacterial load is at its minimum level of no higher than 10² cfu/ml.

Growth and changes in the mid-gut cell morphology of Penaeus monodon juveniles were evaluated after feeding for 35 days with semi-purified diets deficient in water-soluble vitamins. Diets were prepared by deleting one vitamin at a time from the vitamin supplement consisting of cyanocobalamine, folic acid, thiamine, riboflavin, pyridoxine, niacin, choline, inositol and ascorbic acid. Controls were the complete vitamin diet (control diet 1) and the no vitamin diet (control diet 2). Growth rate was poorest for treatment without vitamin supplement and the inositol and choline-deficient diets. Enhanced growth was observed in prawns fed with the riboflavin-deficient diet. All treatments except control diet 1 showed histopathological changes in the mid-gut cells. Detachment or destruction of the epithelial cells were observed in most cases but more severely in treatments without vitamin supplement followed by inositol, choline and vitamin C.

The influence of various sex ratios and stocking densities on hatchery production of Nile tilapia, Oreochromis niloticus L., was studied in land-based (concrete tanks) and lake-based (hapa nets) systems. In both hatchery systems, egg and fry production was maximum at a sex ratio of 4:1 females to males and a density of 4 females per m². Seed production varied significantly among treatments at different periods of the year. In concrete tanks, significantly high seed production of 12.98 and 11.77 eggs and fry per spawner per day was obtained in March and August, respectively. In hapa nets, irrespective of sex ratios, 10.18 seeds per spawner were collected daily in March. In relation to the broodstock density in concrete tanks, significantly bigger daily harvests of 13.41 and 13.00 eggs and fry per spawner were produced in late February and March, respectively. In hapa nets, daily harvests of 8.95 and 7.74 eggs and fry per spawner were the highest seed production levels which occurred in April and March, respectively. Seed production was significantly higher in concrete tanks than in hapa nets while insignificant differences (P>0.05) were found among sex ratio and broodstock density treatments.

The minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of 24 drugs for luminous bacteria Vibrio harveyi and V. splendidus were determined. Only chloramphenicol, sodium nifurstyrenate and the nitrofurans (furazolidone, nitrofurazone, nitrofurantoin and Prefuran) showed relatively low MICs and MBCs (<25 µg/ml^-1). The bacteria showed varied responses to chloramphenicol and Prefuran and low sensitivity to oxytetracycline. Chloramphenicol, oxytetracycline and Prefuran are commonly used in shrimp hatcheries. Shrimp larvae showed high survival rates and active swimming movement after 24 h exposure to in vivo bactericidal doses of chloramphenicol, Furacin, nitrofurantoin (protozoa only), oxytetracycline (nauplius only), Prefuran (mysis only) and sodium nifurstyrenate, but the drugs caused deformities in the carapace, rostrum, and setae. Chemical control of luminous vibriosis among shrimp larvae appears limited, based on the efficacy of existing and readily available drugs, because of the possible development of resistant strains of bacteria and the limited tolerance of the shrimp larvae to the drugs.