From 5 May 1981 to 7 November 1981 a total of 122,841 specimens of milkfish fry and early juvenile fishes was collected with the use of a milkfish fry sweeper. Of these, 66,361 or 54.02% consisted of early juvenile stages of 30 species of finfish and the rest were 56,480 milkfish fry of 45.98% of the total collection. The most abundant finfish excluding milkfish fry was Ambassis sp. comprising 59.43% of the total fish catch, followed by Elops machnata, 12.7%; Sillago sihama, 8.66% Gobiidae, 6.11%; Therapon jarbua, 5.49% Stolephorus sp., 2.06%; Chonoporus sp., 1.53%; Mullet, 0.97% and Scatophagus argus, 0.32%. The rest of the species combined comprised less than 1%. Water temperature, pH and dissolved oxygen (D.O.) showed inverse relationships with fish abundance at the early hours of the day (0800H-1200H) but incosistent correlations were noted during night time when these parameters were rather constant. Salinity did not show any correlation to fish abundance although more species were collected after a heavy downpour. Fish catch was higher during low tide than at high tide.

In a study on energy-protein requirements of milkfish fingerlings using semi-purified diets, several gross observations were made on individual milk-fish such as fin and tail rot, yellowish coloration of the abdomen, opacity and swollen adipose membrane of the eyes. The latter abnormality occurred four to five weeks after feeding semi-purified diets. Milkfish eyes with the abnormality were processed for histological analysis. Opacity of the cornea and lens and degeneration of the eye tissues, thickening of the corneal epthelium and oedema of the stromal layers were seen. Necrosis of the iris, slight thickening of the lens capsule, detachment and destruction of the retinal layers were also observed.

Two experiments were conducted to demonstrate the efficiency of phytoplankton as natural feed in fry-to-fingerling production of Tilapia nilotica . In the first experiment, growth and survival rates of fry given a sustained supply of algae increased considerably over the control fed with rice bran. In the second experiment, T. nilotica were grown in "green" water with phytoplankton concentrations adjusted to the following densities (cells/ml): high, 150-175 x 10 super(3); moderate, 90-120 x 10 super(3); and low, 50-60 x 10 super(3). Increasing the algal densities in the rearing medium enhanced growth of fry. Highest weight increments were obtained with high and moderate phytoplankton concentrations.

Sri Lanka has the milkfish (Chanos chanos) seed and water resources for the development of milkfish aquaculture as a new industry. Milkfish fry and fingerlings are present in all surveyed coastal wet lands, but are abundant in Mannar and Puttalam regions. The species enter tidal pools as larvae and develop into juveniles of about 50 mm. FL in one month. The fry and fingerlings are caught with seine net in tidal pools, transported in plastic bags and stocked in ponds and/or lakes. Mortality ranges 2-100% during transport; 2-15% during acclimatization; and 40-50% after 3 weeks in holding tanks. Careful handling and the application of appropriate transportation, acclimatization and nursing procedures would reduce mortality considerably.

The growth, survival and profitability of milkfish (C. chanos ) and prawn (Penaeus monodon ) (averaging 3.1 g and 0.3 g, respectively) grown in five different combinations for 100 days in 500-m super(2) brackishwater ponds in the SEAFDEC Station at Leganes, Iloilo, Philippines were assessed. The treatments with three replicates each were (I) 2,000 milkfish/ha; (II) 4,000 milkfish/ha; (III) 6,000 prawns/ha; (IV) 2,000 milkfish with 6,000 prawns/ha; and (V) 4,000 milkfish with 6,000 prawns/ha. the competition of prawns to milkfish as expressed by the competition index (CI) was 0.03 and 0.15 compared to the competition exerted by milkfish to prawn (0.48 and 0.67). Mean weight gain of milkfish at 2,000/ha was significantly higher (L = 0.05) than those at 4,000/ha in both monoculture and polycuture systems. the monoculture of prawn (III) was significantly higher (L = 0.05) than that of prawns in polyculture with milkfish (IV and V). Likewise, prawns stocked with milkfish at a lower stocking density (IV) grew signficicantly faster than those at higher stocking density (V).

Various extenders, containing potassium chloride, sodium chloride, glucose, sodium citrate, Ringer's solution, cow serum and milkfish serum were used to preserve milkfish (Chanos chanos) sperm at near-zero temperatures (0-4°C) and in liquid nitrogen (?196°C). Milkfish serum was a superior extender in both cases. After 5 days, comparatively good motility (> 30%) and fertilizing capacity (6.7-18.9%) were observed in the near-zero liquid samples, while in other extenders, sperm ceased to show motility after 2 days. The fertilization success of 4-5 days cryopreserved sperm averaged 67.5% (n = 2) with milkfish serum, 60.5% (n = 2) with 400 mM glucose, 58.0% (n = 2) with 150 mM sodium chloride, 41.2% (n = 1) with Ringer's solution and 31.9% (n = 2) with cow serum.

Crude extracts from various regions of the digestive tract of pond grown milkfish were tested forttheir ability to catalyze the hydrolysis of various carbohydrates. The most active carbohydrases were those involved in the hydrolysis of agr-glucosidic bonds. Maltose, trehalose, dextrin, starch and glycogen were rapidly hydrolyzed in the presence of crude extracts from the intestines and the pyloric caeca. High amylase activity was observed in extracts from the intestines, pancreas, pyloric caeca and liver. The intestinal amylase had optimum activity at pH 6.2 and at a temperature of about 50°C. It was active at a chloride concentration of 10 to 40 ppt. The amylase activity in the intestines consistently peaked daily at about noon when the milkfish gut was full. In contrast, enzyme activity was significantly lower at 0030 hrs when the gut was empty. These results are consistent with earlier observations that the milkfish is a daytime feeder and suggest further that intestinal amylase secretion is in phase with the feeding activity of the milkfish. Although the fishes used in this study fed mostly on the naturally occurring algae in the ponds, no cellulase activity was detected in any region of the digestive tract. Less active carbohydrases that were detected include a beta-glucosidase and beta-galactosidase, both of which were of limited substrate specificity.

Shore-caught milkfish fry (late postlarvae) and artificially-bred, laboratory-reared larvae (0-to 20-day old) were preserved in 5% and 10% freshwater-and/or seawater-formalin solutions after measuring their initial weights and/or lengths. The changes in length and weight were observed at regular intervals. Shrinkage in freshwater-formalin (FWF) was less than in seawater-formalin (SWF). The difference in 5% and 10% concentrations of the same solution was not significant. Wild fry showed a final shrinkage of 5.13% of the initial length in 5% SWF and 5.0 7% in 10% SWF. Shrinkage in laboratory-reared larvae varied from 5.09-8.35% according to the age and/or developmental stage, for the same preservation period of 14 days. In estimating the natural length of milkfish larvae preserved in 5-10% SWF, a 5% shrinkage must be considered. The specimens must be kept in the preservative for at least a week before measurement since it takes at least a week for shrinkage to stabilize. Nothing definite could be said, as yet, for the weight changes in milkfish larvae.

The present paper deals with the morphological development of the external genitalia of Penaeus monodon which will serve as a basis for future researches on the reproductive biology of this species. The petasma length is taken as the median linear distance between the anterior and posterior margins of the organ, and the thelycum length the linear distance between the anterior edge of the boss-like antero-median plate and the posterior margin of the lateral plates. A description is given of the metamorphosis of male and female genitalia of P. monodon.

The development of the optomotor reaction (OMR) in milkfish (Chanos chanos), from the larval, through the metamorphic, to the juvenile stage was observed. The period from the appearance of the pelvic fins until the complete disappearance of the finfold was named "metamorphic stage". While the larvae showed strong rheotactic responses, their OMR was somewhat weak. It was clear that the OMR underwent a big change through the metamorphic stage, and became strong and almost perfect in the juveniles.