To address the preference of mud crab farmers for larger size Scylla serrata juveniles (5.0–10 g body weight or BW; 3.0–5.0 cm internal carapace width or ICW), a study was conducted to compare the growth and survival of crab juveniles (2.0–5.0 g BW; 1.0–3.0 cm ICW) produced a month after stocking of megalopae in net cages when reared further in net cages installed in earthen ponds or when stocked directly in earthen ponds. In a 3 × 2 factorial experiment, three stocking densities (1, 3 and 5 ind m⁻²), two types of rearing units (net cages or earthen pond) were used. Megalopae were grown to juvenile stage for 30 days in net cages set inside a 4000 m² brackishwater pond and fed brown mussel (Modiolus metcalfei). Crab juveniles were then transferred to either net cages (mesh size of 1.0 mm) or earthen ponds at three stocking densities. After 1 month, no interaction between stocking density and rearing unit was detected so data were pooled for each stocking density and rearing unit. There were no significant differences in the growth or survival rate of crab juveniles across stocking density treatments. Regardless of stocking density, survival in net cages was higher (77.11±6.62%) than in ponds (40.41±3.59%). Growth, however, was significantly higher for crab juveniles reared in earthen ponds. The range of mean BW of 10.5–16.0 g and an ICW of 3.78–4.33 cm obtained are within the size range preferred by mud crab operators for stocking grow-out ponds.

A number of researchers have applied multivariate methods to elucidate the population structure of fishes. In this study, we also used multivariate techniques to examine meristic and morphological variations in the silver perch, Leiopotherapon plumbeus (Kner, 1864), from three Philippine lakes, namely, Laguna de Bay, Sampaloc Lake, and Taal Lake. We also aimed to determine whether or not there are meristic and morphological differences among the populations of silver perch from the three lakes, considering that this fish species was introduced from Laguna de Bay into Sampaloc Lake and Taal Lake in the late 1950s and early 1970s, respectively. A total of 710 specimens from four different sites were used in the study: 155 each from Binangonan and Tanay areas of Laguna de Bay and 200 each from Sampaloc Lake and Taal Lake. Based on analysis of variance, eight meristic and 26 transformed morphometric characters were selected for subsequent analyses. Nineteen (19) principal components extracted from the 34 significant variables accounted for 82.3% of the variation in the original variables. Factor analysis using varimax rotation produced four factors: factor 1 was dominated by fin measurements while the highest loadings for factor 2 were gill raker counts. Factors 3 and 4 were dominated by various body and head measurements. Cluster analysis showed specimens from Sampaloc Lake and Taal Lake in one group, while majority of the specimens from Binangonan and Tanay are in another cluster. This suggests a closer morphological similarity between specimens from Sampaloc and Taal. Discriminant analysis gave relatively high correct classification rates (76.13–95.50%). Lower gill raker count was the most discriminating variable. Since both the silver perch from Sampaloc Lake and Taal Lake were introduced from Laguna de Bay, the observed clustering and morphological variation could be attributed to similarities and differences in the lake environments. Laguna de Bay is a shallow eutrophic lake, while Sampaloc Lake and Taal Lake are deep lakes. Further studies, however, are needed to determine which of the myriad of biological and/or physico–chemical factors might have the greatest influence on the observed morphological divergence between the source population and transplanted populations that we found in our study.

Some aspects of the reproductive biology of Charybdis feriatus (Linnaeus) were investigated to identify suitable techniques for broodstock management and seed production. Likewise, factors such as ablation, water depth and light requirements affecting survival or reproductive performance were tested. Production of megalops in tanks and juveniles in net cages installed in earthen ponds was conducted. Wild-caught berried females produced a significantly higher number of zoeae per gram body weight (BW) of the female (3300±600) than captive spawners (867±58). Ablated and unablated crabs spawned after a month and ovaries of both had oocytes in all developmental stages after spawning, indicating that ablation was not necessary. Broodstock survived higher when stocked in 1 m-deep water and kept in dark conditions compared with shallow (0.5 m depth) water or ambient lighting. There were six zoea and one megalopa stage. Megalops were produced (survival of 2–22% in 1 tonne or 23–55% in 3 L tanks) when methods for the mud crab Scylla serrata (Forsskål) were used, but feeding with Artemia started only at the Z4 stage. Survival of megalops after 1 month was higher when stocked in net cages installed in an earthen pond (32–82%) than when reared continuously in land-based tanks (5–11%).

Stock enhancement through habitat restoration and habitat release have both been considered as approaches to the management of declining Scylla spp. Prior to stock enhancement trials, the present study was conducted to monitor recruitment and yields of three Scylla spp. in ∼70 ha of natural mangroves in Aklan, Panay, Philippines. Results showed that Scylla olivacea (Herbst, 1796) was the most abundant mud crab species, comprising 95% of the catches over the 4 yr sampling period. Size distribution for this species indicated year-round recruitment with peaks in the numbers of smaller, immature crabs during the summer months. The decreasing mean size at capture, yield and CPUE in terms of weight throughout the 4-yr sampling period is an indication that the area has been subjected to heavy fishing pressure. The constant CPUE in terms of numbers of crabs suggests that recruitment is constant, though this is likely to be lower than in other mangrove areas due to the topography of the site with limited access to the open sea, resulting in relatively low crab abundance and yields. Combined with the fidelity of S. olivacea to the mangrove habitat, this indicates a suitable population for investigation of the effectiveness of a hatchery-release program.

Distribution of nervous necrosis virus in asymptomatically infected orange-spotted grouper Epinephelus coioides was determined by PCR assay in this study. Fourteen different tissues and organs were collected from apparently healthy groupers including seven individuals of broodstock and 17 juveniles with body weight ranging from 4 to 12 kg and from 2 to 9 g, respectively. No cytopathic effects were found in E-11 cells inoculated with filtrates of sample homogenates. However, all the broodstock and juveniles were positive by nested PCR test except for one juvenile. One hundred percent detection rate of the virus was obtained only from the brain.

The toxicity of formalin and trifluralin to the larval stages of the mud crab Scylla serrata was compared in a static bioassay. Prophylactic doses of 5, 10, 15, 20 and 25 μg L⁻¹ formalin and 0.05, 0.1, 0.2, 0.4 and 0.8 μg L⁻¹ trifluralin were used. Toxicity was assessed on the basis of survival of larvae after 24, 48, 72 and 96 h exposure to the test chemicals and metamorphosis to the next larval stage. Result shows that larval survival in all stages was significantly reduced at concentrations of 20 and 25 μg L⁻¹ formalin whereas larvae were able to tolerate all trifluralin treatments. However, larvae became more tolerant to high formalin concentrations as the larval stage progressed. Survival was better at 5, 10 and 15 μg L⁻¹ formalin and in all trifluralin treatments than the control in almost all the larval stages. Faster metamorphosis was observed at 5 and 10 μg L⁻¹ formalin and 0.05, 0.1 and 0.2 μg L⁻¹ trifluralin concentrations. Doses of formalin and trifluralin obtained from the toxicity experiments were applied as prophylaxis to newly hatched larvae in white plastic basins. Prophylactic doses of 5 and 10 μg L⁻¹ formalin and 0.05 and 0.1 μg L⁻¹ trifluralin applied every other day were found to be effective in enhancing survival and larval development to megalopa compared with control. However, no megalopae survived to crab instar in all formalin treatments. Although the use of fungicides in rearing systems resulted in higher survival compared with controls, other strategies (i.e. maintenance of good water quality and hygienic practices in the hatchery) should be further investigated as an alternative to the use of chemicals in hatcheries.

Phytoplankton supports fisheries and aquaculture production. Its vital role as food for aquatic animals, like mollusks, shrimp, and fish cannot be overemphasized. Because of its contribution as a food source for fish, the growth kinetics of Microcystis aeruginosa, a dominant cyanobacterium in the lake, was studied. The regular occurrence of M. aeruginosa is experienced during the months of May to July or from September to November in Laguna de Bay, the largest freshwater lake in the Philippines. M. aeruginosa was collected from Laguna de Bay, isolated, and established in axenic conditions. Data on the growth kinetic parameters for nitrate-nitrogen and phosphate-phosphorus utilization by M. aeruginosa gave the following values: half-saturation constant (K_s), 0.530 mg N. L⁻¹ and 0.024 mg P. L⁻¹ respectively; maximum growth rate (μ_max), 0.671. d⁻¹ and 0.668. d⁻¹ respectively; maximum cell yield, 6.5 and 6.54 log, cells. ml⁻¹ respectively; nutrient level for saturated growth yield, 8.71 mg N. L⁻¹ and 0.22 mg P. L⁻¹ respectively; and minimum cell quota (Q₀), 2.82 pg N. cell⁻¹ and 0.064 pg P. cell⁻¹ respectively. The low K_s value and high maximum growth rate (μ_max) for phosphorus by M. aeruginosa would suggest a high efficiency of phosphorus utilization. On the other hand, the high K_s value for nitrogen indicated a low rate of uptake for this nutrient.

Competition for coastal land use and overexploitation have reduced or degraded mangrove coverage throughout much of their distribution, especially in South-east Asia. Timber production was the initial motivation for early mangrove reforestation projects. More recently, benefits from protection against erosion and extreme weather events and direct improvements in livelihoods and food security are perceived as justifications for such restoration efforts. This study examines the socioeconomic impacts of a community-led reforestation project in the Philippines through a survey of the local fishers. Revenues from mangrove fisheries, tourism and timber result in an annual benefit to the community of US$ 315 ha⁻¹ yr⁻¹. This figure is likely to be considerably more if the contribution of the mangrove to the coastal catch of mangrove-associated species is included. This estimate only includes direct benefits to the community from mangroves, and not intangible benefits such as coastal protection, which paradoxically is perceived by the community as one of the most important functions. More than 90% of all fishers, regardless of where they fished, thought the mangrove provided protection from storms and typhoons and acted as a nursery site and should be protected. Those fishing only in the mangrove perceived more benefits from the mangrove and were prepared to pay more to protect it than those fishing outside. This study concludes that replanting mangroves can have a significant economic impact on the lives of coastal communities. Acknowledgement of the value of replanted mangroves compared with other coastal activities and the benefits they bring to the more economically-vulnerable coastal dwellers should support better informed policy and decision-making with regard to coastal habitat restoration.

The efficiency of Tilapia hornorum to control luminous bacteria in a simulated shrimp farm environment has been reported. However, the effects of different factors such as feed input and the shrimp biomass were not taken into consideration. This study investigated the effect of feeding and increased shrimp biomass on the efficiency of tilapia to inhibit the growth of luminous bacteria. Results showed that feeding enhances the antibacterial activity or improves the efficiency of tilapia to inhibit the growth of luminous bacteria. However, the efficiency of tilapia at a biomass of 500 g/m³ is reduced if the shrimp biomass is greater than 80 g/m³. This explains the discrepancies in the results obtained in the use of tilapia to control luminous bacterial disease in shrimp ponds. The effect of starvation on the bacterial load of tilapia, grouper and milkfish feces and the amount of feces in the intestine was also investigated. Results showed that total bacterial and presumptive Vibrio count of fish feces decreased after 1 week of starvation except for the presumptive Vibrio count of grouper. The amount of feces in the intestine also decreased as starvation progressed. Moreover, bacteria isolated from the three species have antibacterial activity against the luminous bacteria Vibrio harveyi.