An enrichment experiment was performed to evaluate the changes in lipid and essential fatty acid contents of the rotifer Brachionus plicatilis fed with freeze-dried cells of tropical thraustochytrid Schizochytrium mangrovei (Isolate IAo-1). Rotifers starved for 24 h were fed with S. mangrovei cells at 200, 300, 400, 500, 600 and 700 mg L⁻¹. Enrichment was carried out at two periods (Short-term = 5 h; Long-term = 10 h) to determine the optimum time needed for the maximum enrichment of the rotifers. There was an overall significant increase in the total lipid, arachidonic acid (AA) and docosahexaenoic acid (DHA) contents of rotifers after feeding with freeze-dried S. mangrovei indicating the successful uptake of these nutrients in the rotifer's biochemical composition. On the other hand, docosapentaenoic acid (DPA) did not change significantly in enriched rotifers. Results of the present study indicate that both factors, feeding concentrations and enrichment periods, significantly affected the lipid, AA and DHA contents of rotifers. Uptakes of lipid, AA and DHA significantly increased with increasing feeding concentrations except for those fed the highest feeding concentration of 700 mg L⁻¹ for 10 h. Moreover, lipid and AA contents of enriched rotifers were significantly higher during the short-term enrichment period while DHA contents were significantly higher during the long-term enrichment period. Therefore, it is concluded that the feeding concentration of 700 mg L⁻¹ at an enrichment period of 5 h is optimum in the AA and DHA enrichment of rotifers. The strategic scheme of combining the proper amount of enrichment product and the duration of enrichment in boosting the DHA contents of rotifers will effectively ensure a reliable production of nutritionally superior rotifers at a minimal cost. This will ultimately contribute to the success of rearing marine fish larvae in the hatchery.

The black tiger shrimp (Penaeus monodon) is an ecologically and economically important penaeid species and is widely distributed in the Indo-Pacific region. Here we investigated the genetic diversity of P. monodon (n = 355) from eight geographical regions by genotyping at 10 microsatellite loci. The average observed heterozygosity at various loci ranged from 0.638 to 0.743, indicating a high level of genetic variability in this region. Significant departures from Hardy–Weinberg equilibrium caused by heterozygote deficiency were recorded for most loci and populations. Pairwise F_ST and R_ST values revealed genetic differentiation among the populations. Evidence from the assignment test showed that the populations in the West Indian Ocean were unique, whereas other populations examined were partially admixed. In addition, the non-metric multidimensional scaling analysis indicated the presence of three geographic groups in the Indo-Pacific region, i.e. the African populations, a population from western Thailand and the remaining populations as a whole. We also sequenced and analysed the mitochondrial control region (mtCR) in these shrimp stocks to determine whether the nuclear and mitochondrial genomes show a similar pattern of genetic differentiation. A total of 262 haplotypes were identified, and nucleotide divergence among haplotypes ranged from 0.2% to 16.3%. Haplotype diversity was high in all populations, with a range from 0.969 to 1. Phylogenetic analysis using the mtCR data revealed that the West Indian Ocean populations were genetically differentiated from the West Pacific populations, consistent with the microsatellite data. These results should have implications for aquaculture management and conservation of aquatic diversity.

Sediments from underneath fish cages and in mesocosm tanks were examined to establish indicators of diminished organic matter degradation potential of polychaete burrows from increased mariculture activities in Bolinao-Anda, Pangasinan, Philippines. Results showed that simple sediment characteristics may be used as sediment quality indicators to describe the contribution of burrows to biodegradable processes in sediments with extremely high deposition of organic particles. The indicators of diminished organic matter degradation potential of polychaete burrows are low redox potential (-113 to -150 mV for F. Spionidae and F. Eunicidae) at the 1 cm surface layer, absence or decreased size of burrow openings, presence of H sub(2)S, disappearance of apparent Redox Potential Discontinuity Layer (aRPD), formation of black sediment, and presence of Beggiatoa (sulfide oxidizing bacteria) and gas bubbles.

The use of levamisole as an alternative approach to disease prevention and control has been resorted to in aquaculture. Its immunomodulatory effect in several fish species is well documented but its effect on grouper, Epinephelus coioides requires further investigation. To determine its immunomodulatory effect on grouper, juveniles were injected and fed with levamisole. Intraperitoneal injection (IP) at 0 (control), 0.5, 5, 10, 20 and 50 mg levamisole/kg body weight was administered. Grouper were also fed diets containing 0 (control), 125, 250 and 500 mg levamisole/kg supplemental dry diet for 10 days. Hematocrit levels, total and differential leucocyte counts and bactericidal activity were examined 7 days post IP. Three, 5 and 7 weeks after last administration of supplemented feeds, growth and bactericidal activity werie checked. A significant (P<0.05) increase in the total leucocyte count was noted in the injection-treated fish. Granulocyte (19.39%) and monocyte (27.38%) percentages increased while lymphocyte(53.40%) population decreased in the differential leucocyte count. However, hematocrit levels were not affected by levamisole. Bactericidal activity against Vibrio anguillarum increased in treated (injected and supplemented) fish. A significant (P<0.05) increase in weight of juvenileswas observed 10 days after last feeding with supplemented diet. Groupers injected with 0.5 mg levamisole/kg body weight and those supplemented with 125 mg levamisole/kg dry diet exhibited the most significant (P<0.05) changes in parameters tested indicating immunostimulation. Growth (weight gain) and bactericidal activity peaked 5 weeks post administration of levamisole in the feeding experiment. Results of the present study strongly suggest that levamisole can enhance nonspecific defenses in grouper and opens the possibility of using immunostimulants in grouper culture.

The bacterial isolate HJ1, which was identified as a Methylobacterium sp., grew on 2, 2-dichloropropionic acid as the sole carbon source and produced a 2-haloalkanoic acid hydrolytic dehalogenase. This non-stereospecific dehalogenase E (DehE) catalysed the hydrolytic dechlorination of 2, 2-dichloropropionic acid and D, L-2-chloropropionic acid to produce pyruvate and lactate, respectively. The enzyme was purified to homogeneity and characterized. The molecular weight was 36 kDa by SDS-polyacrylamide gel electrophoresis and 72 kDa by gel filtration, suggesting that the enzyme is a protein dimer. The purified enzyme was only inhibited by HgSO₄ and was non-stereospecific to haloalkanoic acids. The K_m value for the hydrolysis of 2, 2-dichloropropionic acid was 0.25 mM. The enzyme removes chloride present on the α-position, but not on the β-position, of a number 2-carbon alkanoic acids.

Kappaphycus striatum var. sacol was grown in two separate studies: (1) at two stocking densities, and (2) at four different depths, each for three different durations of culture (30, 45 and 60 days) in order to determine the growth rate of the seaweed and evaluate the carrageenan content and its molecular weight. The results demonstrated that stocking density, duration of culture and depth significantly (P < 0.01) affected the growth rate, carrageenan content and molecular weight of K. striatum var. sacol. Decreasing growth rate was observed at both stocking densities and at four depths as duration of culture increased. A lower stocking density (500 g m^–1line^–1) showed a higher growth rate for the shortest durations, i.e. 30 days, as compared to those grown at a higher density. Likewise, decreasing growth rate was observed as depth increased, except at 50 cm after 60 days of culture. A 45-day culture period produced the highest molecular weight at both stocking densities (500 g m^–1line^–1 = 1,079.5 ± 31.8 kDa, 1,000 g m^–1line^–1 = 1,167±270.6 kDa). 'Sacol' grown for 30 days at 50 cm (1,178 kDa) to 100 cm (1,200 kDa) depth showed the highest values of molecular weight of carrageenan extracted. The results suggested that K. striatum var. sacol is best grown at a stocking density of 500 g m^–1line^–1, at a depth of 50-100 cm, and for a duration of 30 days in order to provide the highest growth rate, carrageenan content and molecular weight.

Lacking a propensity to emerge over the mud surface, the eel goby, Odontamblyopus lacepedii, survives low tide periods by continuously breathing air in burrows filled with hypoxic water. As with most marine air-breathing fishes, O. lacepedii does not possess an accessory air-breathing organ, but holds air in the buccal-opercular cavity. The present study aimed to clarify how the respiratory vasculature has been modified in this facultative air-breathing fish. Results showed that the gills apparently lacked structural modifications for air breathing, whereas the inner epithelia of the opercula were richly vascularized. Comparison with two sympatric gobies revealed that the density of blood capillaries within 10?m from the inner opercular epithelial surface in O. lacepedii (14.5 ± 3.0 capillaries mm^-1; mean ± s.d., n = 3) was significantly higher than in the aquatic non-air-breathing Acanthogobius hasta (0.0 ± 0.0) but significantly lower than in the amphibious air-breathing mudskipper, Periophthalmus modestus (59.1 ± 8.5). The opercular capillary bed was supplied predominantly by the 1st efferent branchial arteries (EBA1) and drained by the opercular veins, which open into the anterior cardinal vein. Deep invaginations at the distal end of the EBA1 and the junction with EBA2 are suggestive of blood flow regulatory sites during breath-holding and apnoeic periods. It remains to be investigated how blood flow through the gills is maintained during breath holding when the buccal–opercular cavity is filled with air.

Prevalence of monodon baculovirus (MBV) was determined using polymerase chain reaction (PCR) on deoxyribonucleic acid (DNA) extracts from the hepatopancreas of the wild black tiger shrimp, Penaeus monodon collected from 7 sampling sites in the Philippines. These sites are considered as the primary sources of broodstock and spawners used for hatchery operations. MBV was detected from all sites except Palawan during the dry season and Negros Occidental and Bohol during wet season. The prevalence of MBV showed no seasonal, sex and size variations. These results show that MBV is an established viral infection in wild populations of Penaeus monodon in the Philippines. Broodstock collected from the contaminated sites could serve as a reservoir of the virus which could infect the post-larvae used to stock in grow-out ponds.

Mangrove forests have been cleared at an alarming rate over the last century to allow space for settlements, agriculture and aquaculture and are still used today for fuel and construction. However, in the last few decades the value of the range of services and products that mangroves supply are being increasingly appreciated by policy makers. Mangrove replanting is frequently used as a method of restoring ecological function and associated goods and services but this may not be justified as once diverse forests are often replanted with mono-genus stands. In the present study the abundance of the commercially important mud crab Scylla olivacea, a top benthic predator, was used as an indicator of the ecological function of mangrove habitats. Abundance was estimated using catch per unit effort (CPUE) data obtained from an experimental standardized trapping grid. The same commercial traps also catch two other smaller non-exploited competing species, Baptozius vinosus and Thalamita crenata that are discarded by fishers. The relative abundance of these three species was used to separate the effects of habitat from fishing pressure and recruitment limitation. Four sites on Panay Island, central Philippines were selected to represent different types of mangrove habitat; a replanted fringing area predominantly of Rhizophora spp., a natural fringing area predominantly of Sonneratia spp., a diverse natural basin mangrove area and a degraded mangrove site. The relative abundance of mud crabs was found to be equivalent in the natural fringing mangrove (1.89 crabs trap⁻¹ day⁻¹) and the replanted mangrove area (1.71 and 0.81 crabs trap⁻¹ day⁻¹). Lower densities of S. olivacea in the basin mangrove area (0.33 crabs trap⁻¹ day⁻¹) appear to be due to limited recruitment, and at this site there was instead a higher abundance of the other non-commercial crab species. No mud crabs were caught in the degraded mangrove area and CPUE for other crab species was also low. Overall, the study suggests that replanting of mangroves even in mono-genus stands was effective in restoring mud crab populations, indicating recovery of an ecological function to a level equivalent to that of natural mangrove environments. The use of CPUE as an indictor of relative abundance of S. olivacea was supported by single release mark–recapture studies and a multiple release mark–recapture study in the replanted mangrove site.

Early larval stages of mud crab Scylla serrata were exposed to different concentrations of nitrite (40, 80 and 160 mg L⁻¹ and a control, without added nitrite) and three salinity levels (25, 30 and 35 g L⁻¹) using a static renewal method. No interactive effect of nitrite and salinity was detected. Estimated LT₅₀ in 96-h toxicity tests decreased in all stages with increasing nitrite concentrations in all salinity levels. The 96-h LC₅₀ values of nitrite-N were 41.58, 63.04, 25.54, 29.98 and 69.93 mg L⁻¹ for zoea 1, 2, 3, 4 and 5 respectively. As the larvae grew, they showed a progressive increase in tolerance to nitrite. The toxicity of nitrite to larvae increased with exposure time. The median lethal concentration was not affected by salinity. The chloride component of salinity within 25–35 g L⁻¹ did not seem to be as effective in alleviating toxicity as has been reported in other crustacean species. Based on 96-h LC₅₀ and an application factor of 0.1, the ‘safe level’ of rearing mud crab larvae was calculated to be 4.16, 6.30, 2.55, 2.99 and 6.99 mg L⁻¹ nitrite-N for zoea 1, 2, 3, 4 and 5 respectively.