The effects of salinity on the embryonic development, growth, and survival of D-larvae to plantigrade as well as settling in Placuna placenta were studied. Embryos were developed to D-larvae of shell length (SL) 86±12 μm (SL±S.D.) after 20 h at salinities of 22–34 ppt, but not at lower salinity levels. Percentage production of straight-hinged larvae from fertilized eggs at these salinities ranged from 51% to 63% (P≥0.05). P. placenta larvae survived and settled in salinities of 16–34 ppt. Settlement occurred first (14 days) in salinities of 22–34 ppt and later (19 days) in 16 ppt when SL≥200 μm. Larval size at metamorphosis was not significantly different among these salinities (P≥0.05). Percentage survival of plantigrades at 34 ppt (13%) was significantly higher (P≤0.05) than at 16 ppt (4.5±3%), but not greater than at 22 (6.3±3%) or 28 ppt (7±4%) salinity. The best salinity levels for embryonic development and larval survival at metamorphosis ranged from 22 to 34 ppt and larval growth from 16 to 34 ppt. The tolerance of P. placenta to lower and higher salinities progressively increased as larvae develop from embryo to the plantigrade stage.

Monitoring of the fungal flora of spawned eggs of captive mud crab, Scylla serrata, was conducted in several hatchery runs at the Aquaculture Department of Southeast Asian Fisheries Development Center in Iloilo, Philippines. Quantification of the egg mycoflora revealed the dominance of oomycetes, particularly Haliphthoros spp. among spawners which aborted their eggs prior to hatching. Two species of Haliphthoros (H. philippinensis and H. milfordensis) were identified from the 24 isolates collected. Haliphthoros milfordensis was the dominant species. Physiological studies on vegetative growth and sporulation of the two species show that H. philippinensis have wider optimal range for salinity and temperature requirements than H. milfordensis, especially in sporulation. The pathogenicity study showed that only H. milfordensis was pathogenic to spawned eggs of S. serrata, while H. philippinensis was not. Infection of S. serrata eggs by H. milfordensis was observed starting at two days after inoculation of zoospores with 2-5% infection rate, reaching up to 10% at five days post-inoculation.

The milt production responses of sexually mature sea bass Lates calcarifer to (D-Ala⁶, Pro⁹-N- ethylamide) luteinizing hormone-releasing hormone (LHRHa) and 17α-methyltestosterone injections were examined. At 24 h after injection of a low dose of LHRHa (20 μg/kg BW), the sperm count decreased significantly compared to saline-treated fish, but it returned to pre-treatment levels 48 h after injection, suggesting a possible hydration of the milt. Other milt parameters (milt volume, spermatocrit, sperm production) in LHRHa-treated fish did not vary from their controls at 24 or 48 h after injection but the overall pattern suggested a reduction in milt viscosity. Total expressible milt and spermatozoa collected over the 48-h experiment was approximately three-fold higher in LHRHa-injected fish than in saline-injected fish, indicating a stimulation of spermatozoa production, not merely milt dilution due to hydration. In a second experiment, sperm count and spermatocrit were significantly lower than those of saline-injected fish at 17 and 48 h after a single injection of a high dose of LHRHa (80 μg/kg BW). A methyltestosterone injection combined with the LHRHa injection also resulted in a significantly lower sperm count, but the spermatocrit remained comparable to the control group, suggesting a suppression of the LHRHa-induced milt hydration response. Results demonstrate that LHRHa stimulates milt hydration and spermatozoa production in milting sea bass and that a simultaneous methyltestosterone injection partially suppresses this response.

The occurrence pattern and population dynamics of Acartia tsuensis were investigated in a brackish-water pond in Panay Island in central Philippines by implementing both bi-monthly and daily sampling schemes. A. tsuensis occurred in the pond during the dry season (November-April) when the salinity of the water is in the range of 14 ~ 40 ppt but was completely absent at lower salinities. An almost constant rate of development from the nauplius 2 through to copepodite 5 stages of A. tsuensis was observed both in the pond and in the laboratory. The generation time ranged from 5.9~11.3 days. Fecundity had a positive linear corelation with chlorophyll a. Salinity and chlorophyll a affect the stage duration, mortality, and fecundity of A. tsuensis in the pond.

The effects of alternate starvation and refeeding on food consumption and compensatory growth of hatchery-bred abalone, Haliotis asinina (Linnaeus), were determined. Two groups of abalone juveniles (mean shell length = 29 mm, body weight = 5 g) were alternately starved and refed a macro-alga, Gracilariopsis bailinae at equal duration (5/5 or 10/10) over 140 days. A control group (FR) was fed the seaweed ad libitum throughout a 200-day experimental period. Starved and refed abalone showed slower growth rates (DGR, 63 and 70 mg/day in the 5/5 and 10/10 groups respectively), as a result of reduced food intake (DFI 15% and 16% day⁻¹ respectively), after repeated starvation and refeeding cycles. Percentage weight gains (5/5 = 196%, 10/10 = 177%) were significantly lower than that of the control (397%). When refed continuously over 60 days, the starved groups exhibited increased DFI and fed at the rate of 24% and 25% day⁻¹, which were not significantly different from that of the control at 26% day⁻¹. At the end of the experiment, no significant differences were observed among three treatments in terms of shell length (range: 46–48 mm), body weight (range 25–28 g), % weight gain (392–465%) and per cent survival (range 87–98%). The results indicated that H. asinina had a complete compensatory growth following a return to full rations after a series of intermittent starvation and refeeding cycles.

In an attempt to understand growth regulation in milkfish, the milkfish growth hormone (GH) and its cDNA were characterized and the expression of GH mRNA in embryos and larvae was examined by RT-PCR. The milkfish GH was purified from an alkaline extract of the pituitary by reverse-phase high-performance liquid chromatography and detected as an immuno-positive protein with anti-salmon GH serum. The complete sequence of milkfish pre-GH was determined by cDNA cloning and nucleotide sequencing. On the basis of the N-terminal amino acid analysis of the native protein, the pre-GH was found to consist of a signal peptide of 22 amino acids and a mature protein of 188 amino acids. Milkfish GH shows higher amino acid sequence identity with GHs of carps (91–94%) and salmonids (70%) than with GHs of more advanced teleosts (<60%) in good accordance with its taxonomic position in teleosts. It has five half Cys residues, four of which are at positions homologous with those of other known GHs and the extra Cys with those of carp GHs. The molecular weight of milkfish GH was estimated to be 22 kDa, which is comparable to the theoretical value. This suggests that milkfish GH is a simple protein, although it has two potential N-glycosylation sites. Semiquantitative RT-PCR showed that GH mRNA expression was relatively weak in embryos and newly hatched larvae but was already strong in 2-day old and older larvae.

The effect of different dietary protein and lipid levels, and protein to energy (P/E) ratios on growth and body composition of the mud crab, Scylla serrata, was evaluated. Six practical test diets were formulated to contain three protein levels (32%, 40% and 48%) at two lipid levels (6% and 12%), each with P/E ratios ranging from 20.5 to 31.1 mg protein/kJ. Individual crabs were stocked in 36 units of 60-l tanks and maintained on a 40% protein diet until each molted (M₀). Newly molted crabs were weighed and fed the test diets until termination at 30 days from the third molt (M₃₊₃₀). Crabs were monitored daily and body weight (BW) taken after each molt, at intermolt and at termination. Average initial BW (11.18±0.66 g) was taken at 18 days after M₀. Carapace width (CW) at M₃₊₃₀ and of the exuviae (at molt 1, 2, and 3 or M₁, M₂ and M₃), weight of exuviae (M₁ to M₃), feed conversion ratio or FCR, duration of intermolt, and total number of days of feeding test diets (M₀ to M₃₊₃₀) were determined. At the end of the study, crabs were freeze-dried for analysis of nutrients in the flesh, exoskeleton and fat body. The FCR (3.21–4.21), intermolt duration and total number of days of feeding test diets (111.3–131.2 days) were not affected by dietary treatments (P>0.05). Analysis of covariance was used with CW at M₁ and BW at M₀₊₁₈ as covariates. CW in the 40% protein with 6% lipid or 40/6 diet (P/E ratio, 27.5 mg protein/kJ) did not increase when lipid was increased to 12% (40/12), and it was significantly wider than crabs fed the 48/6 and 48/12 diets (P/E ratios, 31.1 and 27.2 mg protein/kJ). CW and BW did not differ in the 40% and 32% protein diets and were not affected by dietary lipid level at every level of protein. Ca in the exoskeleton was lowest in the 32/6 diet, while exuviae weight was about one-fourth of BW. Crude fat in the lipid deposit of crabs fed 48% protein diets were low. Results showed that the mud crab, S. serrata, grow well when fed diets containing 32–40% dietary protein with either 6% or 12% lipid at dietary energy ranging from 14.7–17.6 MJ/kg.

Growth and survival of hatchery-bred Asian catfish, Clarias macrocephalus (Günther), fry reared at different stocking densities in net cages suspended in tanks and ponds were measured. The stocking densities used were 285, 571 and 1143 fry m⁻³ in tanks and 114, 228 and 457 fry m⁻³ in ponds. Fish were fed a formulated diet throughout the 28-day rearing period. Generally, fish reared in cages in ponds grew faster, with a specific growth rate (SGR) range of 10.3–14.6% day⁻¹, than those in cages suspended in tanks (SGR range 9–11.3% day⁻¹). This could be attributed to the presence of natural zooplankton (copepods and cladocerans) in the pond throughout the culture period, which served as additional food sources for catfish juveniles. In both scenarios, the fish reared at lower densities had significantly higher SGR than fish reared at higher densities. In the pond, the SGR of fish held at 228 and 457 m⁻³ were similar to each other but were significantly lower than those of fish held at 114 m⁻³. The zooplankton in ponds consisted mostly of copepods and cladocerans, in contrast to tanks, in which rotifers were more predominant. Per cent survival ranged from 85% to 89% in tanks and from 78% to 87% in ponds and did not differ significantly among stocking densities and between rearing systems. In conclusion, catfish nursery in cages suspended in tanks and ponds is density dependent. Catfish fry reared at 285 m⁻³ in tanks and at 114 m⁻³ in ponds had significantly faster growth rates than fish reared at higher densities. However, the desired fingerling size of 3–4 cm total length for stocking in grow-out culture can still be attained at stocking densities of 457 m⁻³ in nursery pond and 571 m⁻³ in tanks.

Six microsatellites were used to study (1) the genetic diversity of wild Penaeus monodon shrimp from four geographic regions (Palawan, Quezon, Capiz and Negros Occidental-W) in the Philippines, and (2) its association with the status of mangroves and intensity of shrimp culture systems in these regions. Two cultured populations (Negros Occidental-C and Antique) were used for comparison. All six microsatellite loci were polymorphic. A total of 184 different alleles were found over all loci. The total number of alleles per locus ranged from 6 to 54, with allele size ranging from 159 base pairs (bp) to 400 bp. The observed heterozygosity of the six loci ranged from 0.47 to 1.00. The number of genotypes per locus ranged from 5 to 70. F_st values showed significant genetic differentiation among the four wild populations. Genetic differences between wild populations were also detected by pairwise comparison based on genotypic and allelic frequencies. Genetic differentiation among wild populations exhibited a positive correlation with mangrove status and intensity of culture systems at P=0.083. The Negros Occidental-W population, which originated from an area with the most severe mangrove loss and the most intensive culture systems, was the most significantly differentiated population. It also showed less genotypes per locus than the other three wild populations, suggesting a decrease in genetic diversity in this population. The population from Capiz, a province with a wide area of extensive culture ponds and few remaining secondary mangroves was the second most differentiated population. The Quezon population, which originated from an area with a few extensive culture ponds and less mangrove destruction, was not genetically different from the Palawan population, which was from a pristine site with mostly primary mangroves and no major aquaculture industry. The cultured populations showed less genetic diversity and were significantly different from the four wild populations based on pairwise F_st values and pairwise comparisons of allelic and genotypic frequencies. The results suggest that (a) there was a significant genetic differentiation among the wild P. monodon populations in the Philippines, and (b) the cultured populations were significantly differentiated from the natural populations. More replicate samples from each of the geographic regions are needed to conclusively determine the possibility of an association between genetic differentiation and the status of mangroves and/or intensity of shrimp culture systems.

Two independent experiments on mud crab (Scylla serrata, Portunidae) fattening were conducted simultaneously in 150 m² ponds for 30 days: Expt. I - monosex male (286 ± 1.2 g) vs. monosex female (267 ± 0.9 g) stocked at 0.5·m^-2, and Expt. II - monosex male (338 ± 3.1 g) or female (338 ± 2.8 g) vs. mixed sex (338 ± 3.4 g) stocked at 0.25·m^-2. The crabs were fed daily a mixed diet of 75% brown mussel flesh and 25% fish bycatch at 10% of the crab biomass. Intermolt full male crabs weighing ≥ 400 g and roed females ≥ 350 g were partially harvested from the ponds after 20 days of culture using lift net and current method. Results of partial harvest from all treatments in both experiments showed a total yield of 51-55% of the total initial number of stocked crabs (450 crabs in Expt. I, and 338 crabs in Expt. II). From this partial harvest, crabs in Expt. I attained a mean final body weight of 496 g, a specific growth rate (SGR) of 2.75% in males and 432 g, SGR of 2.4% in females. Expt. II gave a mean final body weight of 520 g (males), 484 g (females), and 517 g (mixed sex) and SGR of 1.1, 0.73 and 0.81, respectively. Results of total harvest showed that the overall mean final body weight (372 ± 4.5 g) of monosex male crabs in Expt. I was significantly higher (P < 0.05) than monosex females. However, specific growth rate, carapace length and width, survival, and production were not significantly different (P > 0.05) between monosex males and females. On the other hand, growth and production of monosex crabs in Expt. II was not significantly different (P > 0.05) from mixed sex crabs. However survival of monosex crabs (100%) was significantly higher (P < 0.05) than mixed sex crabs (87 ± 1.88%).