Erythromycin and oxytetracycline uptake by the giant freshwater prawn, Macrobrachium rosenbergii , was evaluated by the two-step osmotic infiltration technique. Test prawns were immersed in 7.5% NaCl conditioning (hyperosmotic) solution for 30 min. then transferred to a freshwater (hypo-osmotic) solution containing 10 mu g/ml of antibiotic. Antibiotic uptake was determined in test and control prawns at 5, 10, 20 and 40 min. Maximum concentration of erythromycin was observed in test prawns 10 min. after exposure, whereas the same concentration was not achieved in control prawns until 40 min. Oxytetracycline uptake was similar in treated and control prawns in that maximum tissue levels were observed after 40 min. in both cases. The uptake of erythromycin was significantly greater in prawns treated for 10 min. than in prawns treated for 5, 20 and 40 min. Osmotic infiltration did not significantly enhance oxytetracycline uptake at all time intervals tested.

Broodfish of grouper (Epinephelus salmoides ) were induced to spawn by hormonal induction. The hormones used for this experiment were HCG + pituitary gland (PG) and LRH-a. The results showed that at dosages of 500 IU HCG + 3 mg of PG per kg of fish for first injection and 1,000 IU HCG + 3 mg of PG per kg of fish at the final injection at an interval of 24 hours, the treated fish spawned naturally in a spawning tank 12 hours after the final injection. At lower dosages of 500 IU HCG + 3 mg PG at 12-hour intervals or 500 IU HCG + 3 mg PG at 24-hour intervals or using 10 mg LRH-a at 12-hour intervals, the eggs can be artificially fertilized only by stripping. The larval rearing experiment was conducted in a 250-l fiberglass tank at the stocking density of 2,500 larvae per tank. Feeds used in this experiment were: (a) Isochrysis + sea urchin eggs; (b) Isochrysis + Brachionus ; and (c) Tetraselmis + Brachionus . The results showed that newly hatched larvae fed with Isochrysis mixed with sea urchin eggs and then Brachionus from day 10 had the best survival rate (9% at day 30).

Two isolates of Aeromonas hydrophila biovar hydrophila and two isolates of Pseudomonas-like bacteria cultured from milkfish, Chanos chanos, fingerlings stocked in Laguna Lake(Philippines) pens after transport were tested for virulence against healthy milkfish fingerlings. Various combination of bacterial and different routes of inoculation (intraperitoneal injection, bath treatment of scaled fish and bath treatment of unscaled fish) were tested. Results show that bacterial entry in the pathogenesis of the test bacteria to challenged fish is more effective in fishes with scales removed than in uninjured fish or though intraperitoneal injection. The minimum lethal dose of A. hydrophila to scaled fish appeared less than 10⁵ cells/ml of water medium. For Pseudomons-like isolates, the minimum lethal dose was at the level 10⁵ cells/ml of water medium. Fish mortalities significantly increased on day 2 in all bacteria but A. hydrophila was significantly more virulent than the Pseudomonas-like inocula. When A. hydrophilawas injected intraperitoneally into undamaged fish, the maximum dose of 10⁷cells per 2-g fish was needed to cause significant moralities. In general, virulence of the isolates was directly proportional to dose as well as to the length of exposure. A cute signs of bacterial infected scaled milkfish. Lethargic fish displayed spastic and unbalanced swimming movement before death. The virulence of the bacteria as evaluated in this study should lead to further investigation on the role of extracellular factors in bacterial pathogenesis to milkfish fingerling.

Oysters (Crassostrea iredalei ) from a commercial growing area in Capiz, Iloilo, Philippines, were purchased from the Iloilo City Central Market and used in a depuration trial within 24 hours of collection. Total coliform (TC) and fecal coliform (FC) levels were determined using the five-tube, most probable number (MPN) technique. Samplings were carried out in three areas in the tank: (a) near the water trickle are, (b) at the middle and (c) near the water outflow area. FC proved to be a better and more consistent indicator of depuration efficiency than TC which gave erratic levels in the first 24 hours. The oysters with initial FC MPN of 2.2 x 10 super(5)/100 g meat depurated to acceptable levels (< 230 MPN/100 g meat) after 48 hours except those in the middle of the tank (490 MPN/100 g). This suggests the presence of an "indifferent" or "dead" spot. Nevertheless, the same oysters depurated successfully within 72 hours. Ranges of chemical and physical parameters in the depuration water were: temperature, 27.0-29.5 degree C; salinity, 30.5-32.0 ppt; and dissolved oxygen, 4.0-6.2 mg/l.

The feeding habits of Siganus guttatus larvae were determined in laboratory rearing studies at 23.8-30.3 degree C by examination of digestive tract contents of larvae given rotifers and/or brine shrimp. Larvae were initially fed on rotifers at a total length (TL) of 2.6 mm (day 2 from hatching), and on brine shrimp at 4.4 mm TL (day 12). A change in feeding habits, seen as the flexion point in the relationship between larval TL and maximum amount of prey, occurred at about 7.0-9.5 mm TL with rotifers as prey, and at 7.2 mm TL with brine shrimp. Higher preference for brine shrimp over rotifers was seen in larvae 8-9 mm TL and larger. These changes in habit coincided with the full osteological development of the feeding apparatus in larvae at 7-8 mm TL. S. guttatus larvae exhibited a diurnal feeding pattern at day 9 (mean 3.7 mm TL), day 15 (5.8 mm TL) and day 21 (7.9 mm TL).

The effect of molting on osmotic, chloride, calcium and total protein concentrations in the hemolymph of the shrimp Penaeus monodon was investigated. Regardless of medium salinity, tissue water as well as osmotic and chloride concentrations in the hemolymph became stable within one day after molting. In general, total protein concentrations remained stable throughout the molting cycle. Large fluctuations in hemolymph calcium were observed 0-6 hours after molt. In low salinities, hemolymph calcium peaked at 3 hours postmolt to values 30% higher than those during molt. These values subsequently decreased rapidly one after molting, when hemolymph concentrations achieved intermolt values. At 44 ppt, calcium concentrations were highest during molt, then gradually declined by about 15% to intermolt values.

Long-term (1975-1977) collections of larval and juvelnile fish were made from 1) onshore, a sandy beach flanked by a coral terrace and a river mouth, and 2) 500m offshore in 30 m deep water in Pandan Bay. About 70 species in 47 families were recorded onshore and 120 specis in 74 families were recorded offshore over the two-year period. About 60 species were common to both stations. Metamorphic stage Mugilidae dominated the onshore catch (75% of 587 samples), followed by Ambassis ssp. (55%) and Chanos chanos (48%). Predominant in the offshore station were larval Stolephorus spp. and Sardinella spp., occurring in 79% and 62% of 345 samples, respectively. Apogonidae, Leiognathidae, Gobiidae, Dussumieria sp., Caesio spp., Upeneus spp. larval, and the neotenic fish, Schindleria praematura, each occured in 20-40% of the offshore samples. Siganus spp., Lutjanus spp., Sphyraena spp. occured in considerable numbers onshore. Offshore, the first two species occured in higher, and the latter two in lower relative abundance. Mugilidae and Chanos chanos were also relatively less abundant offshore. Larvae of many inshore and pelagic fishery species like Carangidae, Scombridae and Bothidae occured at the offshore station together with larvae of coral reefs species like Pomacentrus spp. and the mesopelagic species like Benthosema spp. and Lestidiops sp.

Unialgal cultures of Oscillatoria quadripunctulata, Chroococcus dispersus, Navicula notha, Euglena elongata, and Chlorella ellipsoidea were fed to tilapia fry for 30 days. Mean weights and survival rates of the fry were highest when given Navicula (105.6 mg, 86%) and Chroococcus (89.1 mg, 90%). Oscillatoria, a filamentous cyanophyte, showed limited acceptability to tilapia fry, possibly because of its larger size in comparison with Chroococcus. Fry fed Chlorella and Euglena did not survive at all. C¹⁴-labeled algae of the above species were fed to tilapia fry of varying ages. Assimilation rates per fry after 24 hours of feeding with a suitable algal species increased with the age of the fry. Moreover, the same trend as in the growth and survival experiments was observed, i.e., the highest assimilation rates were obtained in 40-day old tilapia fry given Navicula and Chroococcus as natural feeds. On the other hand, negligible amounts of the other three algal species tested were assimilated by tilapia fry. The above results were explained in terms of the enzyme secretion of tilapias. There seemed to be no transition stage in the feeding habit of both fry and adult tilapia. The acceptability of plant matter in the diet of even the early larval stages was demonstrated.

A detailed account is given of milkfish farming procedures generally practised in the Philippines. The following phases are identified: 1) collection and/or procurement of seed for fry phase; 2) fry rearing; 3) culture and production in grow-out ponds; 4) milkfish culture and production in freshwater fish pens. Harvesting and post-harvest handling are described. Problems and constraints of milkfish farming in the Philippines are also examined.

Recent developments in milkfish breeeding include succesful induced spawning of wild^1,2 and captive^3-5 fish and spontaneous spawning of broodstock.⁶ Gravid spawners, however, are available only during the wild or are reared in captivity. The seasonal and uncertain supply of wild fry is a major constraint in efforts to increase production of this important food fish in the Philippines, Indonesia, and Taiwan. Gonad devepolment can be induced in some fish by hormone administration. This has been recently reviewed by Lamp⁷ and other workers.^8,9 Induced gonad development using purified salmon gonadotropin have been reported in Salmo gairdneri,¹⁰ Oncorhynchus gorbuscha,^11,12 and Mugil cephalus.^13,14 Hormones are usually administered by injection at frequent intervals in these studies. To reduce stress from frequent handling, a slowrelease hormone cholesterol pellet was with success in Salmo auratus and Ophicephalus striatus.¹⁶ Recent literature suggests that vitellogenesis in fish (at least yolk granule or gobule formation) is under control of estrogen and a pituitary factors. Estrogen stimulates the liver to produce vitellogenin, while the incoporation of vitellogenin into oocytes requires a pituitary factor which may not be the glycoprotein (Con A II) gonadotropin.⁷ In the light of this information and in anticipation of a synergistic role of thyroid hormone ,¹⁷ a combination of fish pituitary extract, estrogen and thyroxin was used in some of our experiments. Our attempts to induce gonad development in sexually immature milkfish and rematuration of regressed fish have not been sucessful to date. This paper presents the experiments done and discusses factors possibly contributing to the negative resp[onse in this fish.