Larvae of the oyster Crassostrea iredalei were reared in the laboratory from eggs through settlement. The oysters were induced to spawn by increasing the temperature by 5-10°C and sometimes by adding stripped oyster sperm to the spawning dishes. Eggs avareaged 48 µm in diameter. The straight-hinge veligers appeared 22 to 26 h after fertilization. The larval shell length increased from 64 to 84 µm in the straight-hinge stage, from 85 to 275 µm in the umbo stage, and from 210 to 275 µm in the pediveliger stage. Eye-spotted pediveligers were observed mostly at lengths greater than 225 µm. The hinge line did not increase much with larval growth. Although length was initially greater than height, the increase in height was much faster due to the development of the umbo. Height was greater than length in more advanced larvae. Valve growth was asymmetrical and unequal, with the left valve generally larger. Settlement and metamorphosis occurred 20 days from fertilization at lengths of 270 µm and greater, when the oyster larvae were reared at 26.5 to 30°C and salinities of 30 to 32 ppt. The larval hinge structure consisted of minute dentition on the central portion of the provinculum and large rectangular teeth on both ends. These teeth became obscured in advanced larvae due to the skewed development of the umbo. Data derived from the laboratory culture of larvae of Crassostrea iredalei may be used in spatfall forecasts for the collection of larvae from the wild and as baseline information for the hatchery culture of oyster larvae.

Development of fin-supports and fin-rays was observed in larval and juvenileChanos chanos, Chondrification of the caudal complex started at 4.70 mm SL. Ossification of the caudal elements started at 7.80 mm SL and was nearly completed at about 30 mm SL. Cartilaginous fusion of caudal elements, which occurs in hypurals of higher teleostean fishes but is not seen in lower teleosts, was observed between the neural arch of the preural centrum 1 and that of the ural centrum 1 via a small cartilage bridging the distal tips of the two arches. Caudal finrays began to develop at 6.60 mm SL, and an adult complement of principal rays was attained at 7.35 mm SL. Dorsal and anal pterygiophore elements were first evident at 6.70 mm and 6.65 mm SL, respectively. All proximal radiais were formed at 8.15 mm SL in both fins. Formation of dorsal and anal fin-rays started simultaneously at 8.60 mm SL, and adult fin-ray complements were attained at 10,00 mm and 10.70 mm SL, respectively. In the pectoral fin, the cleithrum, coraco-scapular cartilage and blade-like cartilage (fin plate) had already been formed at 4.65 mm SL. The mesocoracoid was observed to originate from the coraco-scapular cartilage and become detached from it in the course of ossification. Pectoral fin-ray formation started at 13.80 mm SL and was completed in number of rays at 20.00 mm SL. In the pelvic fin, the basipterygium was first evident at 13.00 mm SL. Pelvic fin-rays appeared at 13.80 mm SL and attained their adult count at 17.15 mm SL.

Increasing fish production through polyculture was clearly demonstrated to the fishfarmers in Laguna lake. The rearing of different species of fish of proper number and species combinations had resulted to the efficient utilization of all the available food niches/zones in the lake. Fish production is site specific in Laguna lake. Wide variation in growth increment and fish yield were observed among the different bays and among farm sited within a bay. The final mean weights of the fish species were 355 mg to 2300 g for bighead carp, 32 g to 103.3 g for tilapia and 8.3 g to 1800 g for common carp.

The in vivo effect of mycostatic levels of fungicides against the fungi Lagenidium sp. and Haliphthoros philippinensis was tested on Penaeus monodon eggs and larvae. Hatching rate and survival of nauplii, zoeae, myses and postlarvae exposed to 10 mg/l benzalkonium chloride, 1 mg/l Clotrimazole, 1 mg/l crystal violet, 10 mg/l 2,4-D, 10 mg/l Daconil, 20 mg/l laundry detergent, 1 mg/l Econazole nitrate, 10 mg/l Resiguard, 0.2 mg/l and 10 mg/l Treflan-R, and 0.01 mg/l and 0.2 mg/l trifluralin were monitored daily for 96 h in a static bioassay in glass aquaria. Test chemicals did not have an inhibitory effect on hatching rate but survival rate of hatched nauplii was significantly reduced in most treatments except those with 0.2 mg/l Treflan-R and 0.2 mg/l trifluralin. Tests with zoeae, myses and postlarvae indicated that 0.2 mg/l Treflan-R as well as 0.01 mg/l and 0.2 mg/l trifluralin did not adversely affect survival. In addition, application of 10 mg/l benzalkonium chloride caused no significant mortalities among exposed myses.

The milkfish, Chanos chanos Forsskal, does not reach gonadal maturity easily in captivity. In an attempt to induce maturation, exogenous hormones, LHRH-A and 17α-methyl-testosterone, were implanted into adult milkfish either alone or in combination. The hormones were delivered using cholesterol pellets (LHRH-A) or silastic tubing sealed with elastomer (17α-methyl-testosterone). The fish were implanted three times at monthly intervals between March and May of 1985. The combination of LHRH-A and 17α-methyl-testosterone induced significantly more maturing fish (P < 0.05) than LHRH-A alone or sham controls; 88%, 38%, and 13%, respectively. Fish with average egg diameters between 768 μm and 905 μm, spawned 48 h after hormone implantation. These results indicate that the maturation and spawning of milkfish in tanks can be induced and accelerated 1–2 months earlier than the beginning of the normal spawning season through hormone implantation.

The spawning behavior and embryonic and larval development of Siganus guttatus are described from laboratory observations. Characteristic prespawning behavior began 4 h before actual spawning: the female touched the anal region of the abdomen on the bottom of the tank; the male displayed short, jerky, rushing movements towards the female, often with rapid circling around her. The male and the female separately released small amounts of milt and eggs several times during the pre-spawning ritual. The color of both sexes changed, the male becoming lighter and the female darker in ground color. Spawning took place at 02.30 h on the third day after the first quarter of the moon. During actual spawning, the pair swam side by side, with the female slightly ahead of the male. Fertilized eggs were small (0.56±0.008 mm), demersal and adhesive, with many oil globules. Larvae measured 1.74±0.043 mm total length at hatching, and possessed eight pairs of free neuromasts with long cupulae (60–180 μm) from 6 h to 39 h after hatching. The adult complement of fin ray counts was attained on day 16 when larvae (=juveniles) measured 8.34 mm total length on the average.

1. Osmolality and chloride concentrations in the hemolymph of Penaeus monodon became stable 1 day after molting in 32 ppt, while total protein and calcium concentrations remained stable throughout the molting cycle. When intermolt (≥ 36 hr postmolt) animals were transferred from control (32 ppt) to experimental (8–40 ppt) salinities, osmolality, chloride and total protein, but not calcium, concentrations in the hemolymph achieved steady state values 24–48 hr after transfer. 2. The hemolymph osmolality was a linear function (slope = 0.28) of medium osmolality at salinities between 8 and 40 ppt. It was isosmotic to seawater at 698 mOsm (10 g prawns) and 752 mOsm (30 g), and was hyperosmotic to the medium below isosmotic concentrations, and hypoosmotic to those above. 3. Hemolymph chloride concentration was isoionic to seawater at 334 mM, and was hyperregulated below isoionic concentrations, and hyporegulated to those above. 4. P. monodon maintained its hemolymph calcium concentration between 6.4 and 10 mM when medium salinities increased from 8 to 40 ppt. 5. Total protein concentration in the hemolymph was independent of medium salinity (8–40 ppt) and hemolymph osmolality (540–850 mOsm).

Experiments were conducted to determine the tolerance of Siganus guttatus eggs to salinity changes. In the first run, the female was induced to spawn spontaneously by using human chorionic gonadotropin. The fertilized eggs were transferred to seawater of salinities ranging from 8 to 40‰ either at the blastomere or at the gastrula stage. In the second run, the eggs were stripped from the female and artificially fertilized following the dry method. Results indicated that eggs transferred at gastrula stage were more tolerant to salinity changes than those transferred at the blastomere stage. Hatching occurred at all salinities but was highest at 24‰. Percentage of viable larvae was highest at 24‰ and lowest at 8‰. The larvae that hatched at low salinities were relatively longer than those that hatched at ambient and higher salinities.

The paper discusses the effect of stocking density and holding periods in stunting milkfish fingerlings in brackishwater ponds using twelve units of 144m² earthen ponds. With 15, 20, and 25 fingerlings/m² growth and survival rates were not significant (P<0.05) averaging 13.60g and 83.47%, respectively. Lowest survival (54.52%) and growth rates (10.80g) were obtained in treatment with highest density level of 30 fingerlings/m². Using the density of 20 fingerlings/m² different stunting periods of 6, 9, and 12 months were tried. Survival and growth rates were not significant for 6 and 9 months stunting periods averaging 79.98% and 13.21 g. At longest (12 months) stunting period however survival was lowest (52.05%). In stunting milkfish fingerlings, a density of 15 to 25 pcs/m² could be tried at a stunting period of 6 to 9 months in order to obtain an optimum survival of 81.7% and growth rate of 13.4 g.

This paper provides basic early life-history information on milkfish (Chanos chanos), seabass (Lates calcarifer) and rabbitfish (Siganus guttatus) which may explain in part the observed differences in their survival performance in the hatchery. Egg size, larval size, amount of yolk and oil reserves and mouth size are all greater in milkfish than in seabass, and greater in the latter than in rabbitfish. During the first 24 h after hatching, rabbitfish larvae grow much faster than milkfish and seabass larvae at similar ambient temperatures (range 26°–30°C, mean about 28°C). The eyes become fully pigmented and the mouths open earlier in seabass and rabbitfish (32–36 h from hatching) than in milkfish (54 h). Seabass larvae learn to feed the earliest. Yolk is completely resorbed at 120 h from hatching in milkfish, and yolk plus oil at 120 h in seabass and 72 h in rabbitfish at 26° to 30°C. Milkfish and seabass larvae have more time than rabbitfish to initiate external feeding before the endogenous reserves are completely resorbed. Delayed feeding experiments showed that 50% of unfed milkfish larvae die at 78 h and all die at 150 h from hatching. Milkfish larvae fed within 54 to 78 h after hatching had improved survival times: 50% mortality occurred at 96 to 120 h, and 10 to 13% survived beyond 150 h. Unfed seabass larvae all died at 144 h, while 6 to 13% of those fed within 32 to 56 h after hatching survived beyond 144 h and well into the subsequent weeks. Unfed rabbitfish larvae all died at 88 h, while 7 to 12% of those fed within 32 to 56 h after hatching survived beyond 88 h. A delay in initial feeding of more than 24 h after eye pigmentation and opening of the mouth may be fatal for all three species.