To address the crablet supply shortage for grow-out ponds, two experiments were conducted. The first aimed to identify the optimal combination of stocking density (SD) and culture duration (CD), while the second utilized this combination to determine the most effective ratio of artificial feed (F) to mussel meat (M) for nursery rearing of mangrove crab (Scylla serrata) megalopae into crablets. Each pond-based net cage (1 m² area) was provided with 1 unit each of shelter and feeding tray. The first experiment assessed four SDs (50, 100, 200, and 300 ind.m⁻²) at two CDs (3 and 4 weeks). Results showed that crablets at 50 ind.m⁻² had carapace width (CW) of 17.3 mm and final body weight (FBW) of 0.65 g after 4 weeks while the highest specific growth rate (SGR) of 19%/day was observed at 3 weeks. Although survival rates were higher (80–84%) at SD 50, 100, and 200 ind.m⁻², a higher final harvested number of crablets was achieved at higher SD 200–300 ind.m⁻² of 162 and 215 ind.m⁻², respectively. Using the SD 200 ind. m⁻², the second experiment evaluated 50F:50 M, 70F:30 M, 80F:20 M, and 100F alone on megalopa reared for 3 weeks. Results indicated that the 70F:30 M treatment obtained the highest SR of 69.9%, FBW of 0.28 g, CW of 12 mm, and SGR of 21.33%/day (p > 0.05). Our results indicate that a SD of 200–300 ind.m² and a feed ratio of 70F:30 M for 3 weeks are recommended for optimal growth and maximizing crablet production of Scylla serrata megalopae in nursery rearing.

The aim of this study was to investigate the effect of malachite green on the post-exposure filtration rate of Blood Clam, Barbatia virescens. Blood Clams were collected from the rocky coast and acclimated to laboratory conditions for 18 days. Bioassays were conducted wherein Blood Clams were exposed for 24 h to a clean medium (no malachite green), 0.06 mg l^-1 malachite green, 0.32 mg l^-1 malachite green, 5.06 mg l^-1 malachite green, and then to the same concentrations for 48 h. Filtration rate in all concentrations and malachite green-exposure durations were determined at 0.5, 1, 2, 3, 4, and 6 h. Blood Clams exposed for 24 h and 48 h to 0.32 and 5.06 mg l^-1 had significantly lower filtration rates than the control (p <0.05). Similarly, those exposed to 0.06 mg l^-1 for 48 h showed significant reduction in their filtration rates. The lower rate was associated with longer exposure to malachite green. In addition, Blood Clams exposed for 48 h were not able to improve their filtration rate, although they were transferred to a clean medium for 6 h. The green colouration on Blood Clams’ muscles was also not eliminated. These findings suggest the ecological risk of malachite green to bivalves and its implications to the health of sessile coastal organisms.

Supplementation of probiotics in live feeds and rearing water may improve the growth, survival, and resistance of fish larvae. This study examined the beneficial effect of a commercial probiotic bacteria Lactobacillus casei on the growth, body composition, and stress resistance in early-stage silver therapon (Leiopotherapon plumbeus) larvae. Larvae at 12 d post-hatch (DPH) (9.76 ± 1.32 mm total length [TL] and 13.48 ± 4.80 mg body weight [BW]) were reared in triplicate groups of 15 larvae per tank from 12 – 40 DPH (Phase 1) and 41 – 96 DPH (Phase 2). From 12 – 40 DPH, larvae were fed (I) unenriched Artemia nauplii (no-PB or control group); (II) probiotic-enriched Artemia nauplii (PB); and on (III) probiotic-enriched Artemia nauplii and rearing water (PB + W). The same feeding regime was used from 41 – 96 DPH except that the larvae were co-fed Artemia nauplii and microparticulate diet (MPD). Mean survival rates at 40 (97.78% – 100%) and 96 DPH (86.67% – 91.11%) did not show significant differences among treatments. However, except for body depth (BD) and Fulton’s condition factor (K), mean TL, BW, length increment (LI), and length- (SGRL) and weight-specific growth rates (SGRW) of PB + W-fed larvae were significantly higher than PB-fed and no-PB-fed larvae at 40 DPH. While these parameters were similar among treatment groups at 96 DPH, slightly higher values for BW and SGRW were noted for the PB + W group, as supported by the higher proportion of L. casei to total microbiota in the intestines of early-stage larvae. Whole body protein and lipid contents were highest in the PB + W and PB groups, respectively, but did not differ from the no-PB group. Survival rates (93.33% – 100%) after 18 h exposure to 30 ppt did not show significant differences. However, recovery rates after 15 min of air exposure of early juveniles in the PB and PB + W groups (93.33%) were significantly higher than those fed unenriched Artemia (66.67%). These results indicate that supplementation of probiotic bacteria L. casei in live feed and rearing water may support growth of early-stage larvae of silver therapon and its resistance to stress conditions during culture.

Factors such as nutrition, season, sex ratio and broodstock density affect reproduction in red tilapias. However the extent by which genetic strain differences influence reproductive performance in red tilapias is not fully understood. Hence an experiment was conducted to compare the reproductive efficiency of three genetically diverse Philippine red tilapia strains (“BFS”, “FAC” and “PP’) and one imported Asian strain (“NIFI” from Bangkok, Thailand). Breeders (one male: four females) from each strain were tested in two types of fry production systems (2 m x 2 m x 1 m concrete tanks and lake based 2 m x 2 m x 1 m hapa net cages). Spawning activity, fecundity, and hatchability were monitored and recorded. Seed production in all strains were noted to be lower in cages than in tanks. Daily mean seed production per spawner in the land-based hatchery system was highest at 13.662 for NIFI followed by FAC ( 13.236), BFS (10.966), and PF (7.77). In the hapa net cages, the BFS strain produced 1.137 seeds per female daily while PF, NIFI and FAC gave daily harvests of 0.968, 0.773 and 0.517 seeds per spawner. Seed production was significantly influenced by the type of hatchery system (P = 0,000) , strain (P = 0,021) and strain x hatchery system (P = 0,007), No significant strain differences were found when spawning percentage and hatchability data were analysed.

Our inland waters continue to suffer from pollution. This has resulted in prolonged exposure of fish and other organisms to pollutants. This study was carried out to determine some of the possible long-term effects of exposure to heavy metals in the Nile tilapia, Oreochromis niloticus. One month old 0. nifoticus fingerlings were exposed for 2 months to a mixture of 0.01 mg per 1 Hg, 0.1 mg per 1 Cd and 1.0 mg per 1 Zn. The survivors were grown to sexual maturity in a natural environment (lake) then spawned. Results showed that the exposed 0. niloticus can recover from the prolonged exposure to the metals as demonstrated by their spawning success and fry survival which was comparable to the unexposed group. This could be because the accumulated heavy metals were eliminated by the fish during the lake grow-out phase. By the time the fish were spawned, they have eliminated the 85 to 98% of the heavy metals from their body. The progenies of the exposed parents (EP) were subsequently exposed to another mixture of the three metals: 3.0 mg per 1 Zn, 0.30 mg per 1 Cd and 0.01 mg per 1 Hg, in both static and static-renewal system. Another group from unexposed parents( UP) received the same treatment. Results showed that in both exposure systems, the survival of the progeny of EP was significantly higher (P < 0.05) than the those from UP. Survival was three to five times better in the progenies of EP than those of UP. Exposure of the parental stock resulted in the culling out of individuals which were more susceptible to the heavy metals. The more resistant members of the population (the survivors) which have the ability to adapt to the toxicants were able to pass on the resistance to their offspring. The results are supported by other studies which demonstrate high resistance in populations of organisms living in contaminated sites.

Five marine fish species (milkfish, Chunos chanos; Asian sea bass, Lates calcarifer; grouper, Epinephelus coioides; rabbitfish, S&anus guttatus; snapper, Lutjanus argentimuculatus) and three freshwater fish species (tilapia, Oreochromes niloticus; bighead carp, Aristichthys nobilis; Asian catfish, Clarias macrocephalus) of commercial importance are currently the subjects of breeding and seed production research in the Philippines, primarily at the SEAFDEC Aquaculture Department. Natural and induced spawning of milkfish have been achieved. Although seed production is now a commercial enterprise, work on hormonal induction of off-season maturation is being pursued to obtain fry during periods when these are scarce. Hormone regimes to manipulate spawning and advance maturation in sea bass have been developed, while hormone-induced spawning of rabbitfish and snapper have been achieved. Studies on hormonal induction of sex inversion in juvenile and adult groupers are being undertaken. Research programs to develop and select improved tilapia strains and chromosomal manipulation for production of all-male tilapia hybrids are under way in several aca- demic and research institutions. Work on induced and spontaneous spawning of the Asian catfish, an endangered species in the Philippines, has recently started while research on bighead carp addresses problems such as alternative agents for spawning and declining reproductive performance of inbred stocks. With few exceptions, fish breeding research in the Philippines is production-oriented and empha- sizes development of practical methods adapting those developed for other fish species. Because of technical, institutional, and funding constraints, very limited work can be done to investigate the physiological mechanisms regulating reproduction, development and growth in any of these species. Attempts to apply information gathered from other species to our local species have met with both success and failure, and reasons to explain these results have been mainly speculative. Because of the varied species available for research, there is a wide room in which to investigate specific problems that are currently of interest to comparative endocrinologists. This can only be done in collaboration with other institutions in developed countries carrying out similar research.

The relationship between virulence and overall within-host fitness of the fish rhabdovirus Infectious hematopoietic necrosis virus (IHNV) was empirically investigated in vivo for two virus isolates belonging to different IHNV genogroups that exhibit opposing host-specific virulence. U group isolates are more virulent in sockeye salmon and M group isolates are more virulent in rainbow trout. In both single and mixed infections in the two fish hosts, the more virulent IHNV type exhibited higher prevalence and higher viral load than the less virulent type. Thus, a positive correlation was observed between higher in vivo fitness and higher host-specific virulence in sockeye salmon and rainbow trout. Comparisons of mean viral loads in single and mixed infections revealed no evidence for limitation due to competition effects between U and M viruses in either rainbow trout or sockeye salmon co-infections.

In milkfish farming, when food wastage is high and assimilation is poor, most of the nutrients added to the culture species may ultimately pollute the environment. Assessment of water dispersion from ponds and cages rarely take into account the physical properties of feeds. This study dealt with settling velocity, physical stability, and the amount of nutrients (nitrogen and phosphorus) generated by milkfish feeds alone in water. Four locally manufactured milkfish (Chanos chanos) pelleted feeds labeled as: Grower A, Grower B, Grower C, and Finisher D were tested, with freshwater, brackishwater and seawater as test media. Settling velocities of the four feeds were generally greater in freshwater than in brackishwater and in seawater, ranging from 11.0-11.5 cm s^-1 for 6-8. mm long pellets, and 12.8.0-13.0 cm s^-1 for 9-11 mm pellets with Milkfish Finisher D. In brackishwater, settling velocities of size ranges 6-8 and 9-11 mm long were 9.8-10.0 and 11.0-11.6 cm s^-1 respectively. In seawater, settling rates of milkfish feeds were 8.0-8.5 and 9.8-10.1 cm s-1, for the same size ranges. There was no significant difference on the settling velocities among feed brands tested but significantly different within water types (P> 0.05). Water stability of these pellets was tested within 15, 30, 60 and 120 minutes immersion time. The four-feeds tested showed a range of water stability of 84.4-87% for the first 15 min in seawater, 70-82 % in brackishwater and 74-82% in freshwater. They are not that water stable after one hour with water stability of 35-40%. Nutrient contribution assessment of these feeds was also carried out by submersion test. Total ammonia nitrogen (TAN) concentrations in freshwater generated by the four feeds were low and were not that significant during the first two days. Values abruptly rose above the initial concentrations of 0.04 to 3.25-6.97 mg l^-1 on the6th day of submersion. In freshwater, Grower A had the highest TAN concentration value of 6.97 mg l^-1 and Grower D had the lowest value of 0.1 mg l-1. Nitrite concentration was low at a range of 0.01-0.04 mg l^-1 while nitrate ranged from 0.1-0.76 mg l^-1 for all the feeds. In brackishwater, TAN concentrations steadily rose to a range of 2.5-3.5 mg l^-1 in all feeds, while in seawater a lower concentration than the brackishwater of 0-1.2 mg l^-1 within 7 days of submersion was obtained. Phosphate-P concentrations rose on the second day of submersion in all test media and abruptly fell on the fifth day. Grower B gave the highest phosphate concentration of 1.55 mg l^-1 in freshwater and 1.44 mg l^-1 in brackishwater by the same feed and 2.0 mg l^-1 by Grower A in seawater. ANOVA showed no significant differences among the feeds in terms of N and P concentrations obtained within seven days of submersion (P< 0.05). Nutrient inputs from feed undergo nutrient transformation and nutrient buildup was very apparent especially in freshwater and in brackishwater. The results of this study are measures of the significance of physical properties and nutrient releases of commercial feeds on the water quality of milkfish culture system. Data gathered can be applied into feeding management techniques, selection of good quality feeds and can be incorporated into models defining the impact of pollution from commercial feeds on the environment.

The onset of digestive enzymes in the various regions of the digestive tract of sea bass, Lates calcarifer (Bloch) at days 0. 2, 5, 10, 20, 30, and 40 after hatching was investigated. This study aims to correlate which enzymes are detectable in stated regions of the developing gut and to relate this pattern to the feeding habit of sea bass. Alkaline phosphatase and esterase were localized in the intestine of the 2 day old larvae. At 5 days post-hatching, esterase was present in the esophagus. At the beginning of metamorphosis (20-days post-hatching), alkaline phosphatase, esterase, and amino peptidase were localized in the pyloric caeca. Aminopeptidase's and lipase were observed in the brush border of the intestinal epithelial cells. At the end of metamorphosis (30-days-post-hatching), all enzymes investigated in this study were present. Esterase was demonstrated in the columnar cells of the stomach while lipase and amylase were observed in both columnar cells and gastric glands. Protease and amylase were present in the pyloric caeca and intestine. During the early juvenile stage (40-days-post-hatching), esterase was localized in the gastric glands of the stomach. The appearance of esterase activity as early as day 2 was correlated with endogenous to zooplanktivorous feeding. In the same manner, the presence of aminopeptidase's, lipase, protease, and amylase at day 20 to 30 onwards was related to a change in feeding habit of sea bass from zooplanktivorous to real carnivorous. The findings of this study demonstrate the need for basic studies for feed formulation and management of the fish.