A total of 2497 milkfish fry were collected in 1976 from nine localities in six countries, viz. India, Thailand, Indonesia, Philippines, Taiwan and Tahiti. Vertebra counts ranged from 40 to 45. The general trend of geographical gradient in vertebral counts in the milkfish was observed to be lower in the west (or otherwise, along continents) and higher in the east (or around oceanic islands). Extremes in the means of vertebral counts by localities were seen in the samples from India with 43.08 and from Tahiti with 43.82. It was suggested that there may be at least four subpopulations among the milkfish throughout the tropical Indo-Pacific waters.

The recognition of individual animals is crucial to many aspects of research. Prawns present unique difficulties in this respect since they molt regularly. Thus almost all tagging and marking methods developed for prawns so far have proven inadequate. Some are lost during molting; others cause injury to the prawns. A new and efficient method has been developed at the Igang Sea Farming Station of the Aquaculture Department. Brass tags measuring 5 mm by 20 mm and numbered consecutively are encircled around the eyestalk like a small bracelet. The prawn is gently held at the base of the carapace by the left hand while the right hand slips the brass tag over the eye. The tag is gently pressed around the eyestalk to prevent its slipping out. All tagging is done under water to avoid stress.

In the present study, no visible differences between the sexes of C. chanos with reference to external features such as colouration, shape of head, snout and operculum, presence of tubercles or nasal pores, length, size and shape as well as any roughness in the various fins, could be found. However, the anal region of the mature milkfish (sabalo) exhibits discernible anatomical differences in the male and female. The male has two main openings visible externally: the anterior anus and the posterior urogenital opening at the tip of the urogenital papilla. The female has three main openings instead of two: the anteriormost anus, followed by the genital pore and the urinary pore located posterior to the genital pore at the tip of the urogenital papilla. Internal examinations were also made on both sexes. In ripe sabalo, it is easier to distinguish the sexes since milk oozes out of the urogenital pore by pressing the abdomen of the ripe male fish. Gravid females are identified by their distended abdomens.

Four different postlarval stages (P₁₁, P₁₅ , P₂₁, and P₂₅) of P. monodon were stocked in suspension nets at the rate of 200 fry/sq m with 3 nets for each postlarval stage. Pond bottom was simulated by filling each net with a 15 cm layer of mud; dried twigs were provided for protection of the fry. Feeding with lablab and determination of temperature, dissolved oxygen, pH, salinity and alkalinity were regularly undertaken. Results show higher survival rates for P₁₅ and P₁₈ compared to the other stages.

The Japanese little-neck clam, Tapes philippinarum, an introduced species in Kaneohe Bay, Oahu, Hawaiian Islands, has a thriving population only in a U5-hectare mud flat after heavy fishing triggered depletion in six other beds within the bay. Monthly gonad examination of the clams suggested that spawning occurs at a low level throughout the year with a peak from January to February. This observation is corroborated by the appearance of new recruits in the monthly sample from April to June and by their presence at low levels at other times of the year. Size-specific fecundity, determined indirectly from differences in the length: dry weight relationships of ripe and spent clams, ranges from 432,000 eggs in a 20-mm clam, increasing exponentially to 1.35 x 10⁶ eggs in a 40-mm clam. Estimates of the population of clams 11 mm and larger, which were 3.09 x 10⁶ in 1970 and 3.4 x 10⁶ in 1972, show a growth of 5 percent per year during the 2-year period; monthly quantitative sampling showed no evidence of population growth after 1972. A survivorship curve obtained from the monthly samples gave a total instantaneous mortality of z = 0.2005. The age-specific mortality agrees with the age-frequency of the empty shells collected from the bed, with a correlation coefficient of 0.9345 with 4 d.f. The condition of the empty shells indicated that 57 percent of the mortality is attributable to crab predation, mainly by Thalamita crenata, which constitutes 70 percent of the experimental crab catch in the clam bed. Sixty percent of the broken shells were 19.5 to 30.4 mm in length; in experiments with predation by T. crenata, 96 percent of those eaten fell within the 14.5 to 30.4 mm size range. The difference between the lower limits of the size ranges can be attributed to the size structure of the clams during the survey period. The experimental population had an artificially maintained size structure. Experimental exclusion of predators over a limited area suggested that crab predation regulates clam size structure but not clam density.

The early growth, yolk and oil globule resorption, early morphological and behavioral de-velopment, and initial feeding of hatchery-raised Lates calcarifer were studied. Based on the developmental events and the energy the reby utilized, the early life history of this species can be broken down into the following five phases: 1) rapid early growth due to rapid yolk resorption (from hatching to about 15 hr after hatching (TAH); 2) morphological differentiation and slowgrowth based on energy from yolk (to about 50 h TAH when the yolk is exhausted); 3) slow growth with initiation of feeding and swimming activities, based on energy from oil globule and from exogenous food (to about 110 h TAH); 4) accelerated growth and effective feeding and swimming based on the same two sources of energy as in the preceding stage (up to about 120-140 h TAH when the oil globule is exhausted); and 5) accelerated growth, effective feeding and swimming and further development based solely on exogenous energy (beyond 140 h TAIT).

Milkfish (Chanos chanos Forsskal) reared from wild-caught fry and from hatchery-bred fry matured at 3.5-5.5 years (2.3-4.9 kg). Maturation and spawning of the hatcherybred fish marks the first time the milkfish life-cycle has been completed in captivity. Milkfish at various stages of gonadal development were obtained in July-October 1980 and March-June 1981 derived from wild-caught fry, and in February-June 1983 from the hatchery-bred fish. The fish were held in floating net cages 9 m and 10 m diameter by 3 m deep, located in 7 m deep water off Igang, Guimaras Island, Philippines. Annual ranges of temperature and salinity were 25-33°C and 25-38 ppt, respectively. The fish were fed commercial feed pellet (42% protein) at 1.5-2% of body weight twice daily. Sexual maturation occurred during the natural breeding season of wild milkfish in the nearby waters. Gonadosomatic index (GSI) of mature males was 0.32-3.95 (wild-caught, 0.32-3.95; hatchery-bred, 1.71-3.85). For mature females it was 1.24-8.12 (wildcaught, 1.56-7.62; hatchery-bred, 1.24-8.12). Two spawnings were recorded in August 1980 and eight in May-July 1981 from the broodstock derived from wild-caught fry, with 342-6293 eggs collected from each spawning, while 14 spawnings were observed in May-June 1983 from the hatchery-bred fish, with 770-114 000 eggs collected. The time of spawning was between 23.00 and 02.00 h. Fertilization rate was 55-99% for the broodstock from wild-caught fry and 47-100% for the hatchery-bred fish. Hatch rate varied from 9 to 80%. Factors affecting spontaneous maturation, spawning and rematuration are discussed. Although slight improvements in egg collection were obtained, further innovations in egg collecting techniques will have to be developed. The results indicate the potential for hatchery production of milkfish fry from captive broodstock and for restocking of waters deprived of naturally occurring fry.

Prawn culture is becoming more widespread in the Philippines. In recent years, prawn production in brackishwater ponds has been adversely affected by a chronic soft-shell syndrome. A field survey of prawn ponds in the island of Panay showed that occurrence of soft-shelled prawns could be predicted with 98% accuracy under poor soil and water conditions in the ponds. Some management practices were also highly correlated with the soft-shell syndrome. Soft- and hard-shelled prawns collected during the survey were analyzed for calcium and phosphorus levels. In soft-shelled prawns, calcium and phosphorus levels were significantly higher in the hepatopancreas, and phosphorus was significantly lower in the exoskeleton than in hardshelled prawns. Chitinoclastic bacteria, Vibrio and Aeromonas, were isolated from soft-shelled prawns but experimental infection with these species to induce soft-shelling gave largely negative results. Laboratory experiments using an organostannous pesticide revealed that a 96-h exposure to at least 0.0154 ppm of the pesticide could result in soft-shelling of 47-60% of the prawns. Soft-shelled prawns were fed various quantities of frozen mussel meat for 4 weeks to find out if soft-shelling could be reversed by dietary manipulation. Successful reversal of soft-shelling, general improvement of shell quality, and best growth and survival rates were observed in prawns fed a 14% mussel meat diet.

Penaeus monodon larvae were reared from zoea₁ (Z₁) to mysis₃ (M₃) using two different algal feeds, Chaetocero calcitrans and Tetraselmis chuii. Artemia nauplii were added to both treatments at mysis₂. Mean survival and growth rates in both treatments were different at 5% level of significance on the second and third day of culture, but did not differ during the mysis stage and the end of the 8-day culture period. Z₃ and M₃ larvae fed with C. calcitrans had a lower crude protein but a higher lipid content than T. chuii-fed larvae. Differences in carbohydrate content were noticed in M₃ larvae. The implication of the findings are discussed.

Two-week old milkfish (Chanos chanos ) larvae (7.5 mm standard length, 2.3 mg wet body weight) previously fed only rotifers were weaned abruptly to six artificial diets (commercial feed TP, artificial plankton AS and BP, experimental SEAFDEC diets CT and CB, and moist egg diet) with control larvae fed Artemia nauplii. Survival rates ranged from 38% on moist egg diet to 63% on BP, with 42% in the control. On day 43, larvae attained mean lengths of 7.7 mm on moist egg diet to 13.4 mm on Artemia , with no significant differences between diets. The mean wet weights were highest in larvae fed Artemia (77.8 mg). Results show the feasibility of weaning (gradually) even younger milk-fish larvae in hatcheries, using artificial diets.