Different stages of the white prawn, Penaeus merguiensis de Man, were examined for microsporidian infection. The parasite was found only in adult female prawns exhibiting white instead of the normal olive-green ovaries. Non-germinal tissues were not infected. Spores found in the digestive tract, abdominal muscles, hepatopancreas, heart and gills were extracellular in location and did not have any histopathologic effect on these organs.

Quantitative determination of the algal population, in terms of cells/ml and biomass/ml, was conducted during the first month of growing P. monodon postlarvae in Laguna Lake. Algae were sampled from each side of net cages at depths of 15, 30 and 45 cm below the water surface. Accumulation of algae appeared to be influenced by the direction of water flow. Moreover, growth of algal species was inversely proportional to depth of water. After two weeks, algal biomass was estimated to reach 4.5 kg per cage (1 x 1 x 1 m). Diatoms (Chrysophyta) predominated throughout the experimental period followed by members of Cyanophyta and Chlorophyta.

Polyacrylamide disc gel electrophoresis was done to determine the lactate dehydrogenase (LDH) isozyme patterns for fry (5-3 mg), fingerling (6-12 g), pond-size (150-250 g) and adult (6-9 kg) milkfish. The patterns were tissue specific; the different tissues examined, viz., eye, liver, heart, and skeletal muscle had different expressions of LDH isozymes. The resolved patterns appeared to be products of LDH gene loci A, B, and C. Subunits A and B were present in all tissues. A₄ and B₄ were predominant in skeletal and heart muscle, respectively; the two associated non-randomly in vivo and formed only the heteropolymers A₃B and AB₃. A liver band, L₄, was most conspicuous in the fingerling, pond-size, and adult; it was assumed to be coded by locus C. A negatively charged band, X₄, was detected in fully developed ovary and in fry homogenized as whole individuals, but it could not be resolved in tissues of fingerling. Six-mo old stunts and 3-mo old fingerlings had similar LDH patterns for all tissues examined. The patterns for 11-mo old stunts and fingerlings also were similar but the one for the eye of the former was the same pattern resolved for the eye of adults. There was no change in the LDH isozyme patterns of milk fish stunted for 6 mo under different salinity levels (0-5, 15-20, 32-35 ppt).

Diagnostic features for the identification of postlarval Penaeus found in the shore waters of the Philippines are described and categorized based on specimens caught from the wild and those hatched and reared in the laboratory. Differentiating features for postlarval Penaeus are given which include the relative length of the antennular flagellum, the shape of the rostrum and number of rostral teeth, the antennal spine, the spinules on the dorsal caina of the sixth abdominal segment, and chromatophore patterns. Postlarval Penaeus were classified into two species and two groups as follows: (1) P. monodon, larger in size with dense chromatophores, and the long inner antennular flagellum being more than 2.0 times the outer antennular flagellum; (2) P. semisulcatus, the inner flagellum being 1.6 to 2.0 times the outer antennular flagellum, the the absence of chromatophore on the middle portion of the telson and uropods; (3) P. merguiensis group, less pigmented, the inner flagellum being less than 1.6 times the outer flagellum and (4) P. japonicus group, a short rostum, presence of spinules on the dorsal carina of the sixth abdominal segment, and dense chromatophores. The determinations were confirmed by rearing experiments.

Knowledge on the feeding activity is basic and very important for rearing fish. The information on the feeding activity rhythm of the animal suggests the proper time to feed it. Many devices have been designed to record the feeding activities of aquatic animals. Some are mechanical devices which are difficult to maintain in good conditions for a long time. None of the present devices can be applied to milk-fish because of its characteristic manner of taking food. In this paper, a new electrical device for recording the feeding activity of milkfish is reported.

Milkfish (Chanos chanos) and prawn (Penaeus monodon) were stocked in 500 m2 earthen ponds from 12 November 1978 to 15 March 1979 at the following combinations: 2000 milkfish fingerlings per ha (treatment I); 2000 milkfish fingerlings plus 4000 prawn juveniles per ha (treatment II); and 2000 milkfish fingerlings plus 8000 prawn juveniles per ha (treatment III), with three replicates per treatment. Highest combined net milkfish and prawn production was obtained in treatment III with 492.1 kg/ha followed by treatment II with 404.1 kg/ha, and treatment I (milkfish only) with 280 kg/ha. Differences in combined net production between treatments III and I and between treatments II and I were statistically significant at the 5% level. Average net production of milkfish alone was also highest in treatment III followed by treatment II and treatment I, although differences were not significant. Average net production for prawn was also better in treatment III than in treatment II but the difference was not significant. However, mean weight of prawn was higher in treatment II compared to treatment III. Average survival rates were high for milkfish in all treatments ranging from 90 to 96%, but low for prawn at around 50% for both treatments. There was no significant difference in survival rates of milkfish among treatments and of prawn between treatments II and III. The competition index between milkfish and prawn at the given stocking combinations was negative indicating a positive, advantageous influence of prawn on milkfish production.

Seven stages in the life history of milkfish Chanos chanos are suggested: embryonic, yolksac larval, larval, postlarval, juvenile, sub-adult and adult stages. These were based on morphological differences and on their particular ecological requirements. The latter include: behavioral pattern, food and feeding habits, and habitat requirements. Throughout the life cycle of milkfish the stronger driving force with determines particular behavioral strategies can be attributed to the evolutionary response of the organism of food distribution (availability) followed by predation pressure.

Penaeus monodon juveniles (P₅₃-P₅₄, 0.45 g) were stocked in 200 m² earthen ponds with water exchange rate of 5-10% daily, and reared for 3.5 months. Stocking density levels of 2.5, 5.0, 10 and 20 prawns/m² were designated as treatments A, B, C and D, respectively. Pelletized formula feed was given daily from the second week of stocking at 10% of biomass and was reduced bi-weekly by 1% to a final rate of 5% of biomass. Significantly, high survival was achieved in treatment A, 98.6% followed by B, 95.3%; D, 87.6% and C, 86.5% (P < 0.05). The final average body weight obtained varied inversely with stocking density. Mean body weight for treatments A and B were significantly higher than those of treatments C and B. Results also showed significant differences among all paired means of the final weights except between treatments C and D.

The skull of the milkfish, C. chanos, is described so that it may be used as a tool in identifying the effect of artificial propagation in terms of skeletal malformations.

Haliphthoros philippinensis sp. nov., isolated from larvae of P. monodon is described and illustrated as new. The fungus grew at a temperature range of 13.5-36.3 C, with the optimum of 29.3-34.5 C. Growth occurred in peptone-yeast extract-glucose broth containing 0.3-7% NaCl, with optimum concentrations of 1-4%. At 8% NaCl concentrations, growth was not observed. Its pH range for growth was 5-11.