Morphological changes in the embryos, egg size and development, incubation period and morphological structures of newly hatched zoea of three mud crab Scylla species were determined. The three species exhibited similar embryonic development composed of 10 stages. The mean egg diameter of Scylla serrata was significantly larger (P<0.05) at the prehatch stage. The mean egg diameters of Scylla tranquebarica and Scylla olivacea were similar (P>0.05). The incubation period was the longest in S. serrata and the shortest in S. olivacea. There was a positive relationship between egg size and larval size, as S. serrata exhibited the largest egg size and first zoea. However, no correlation was detected between egg size at prehatch and lengths of the morphological structures of the newly hatched zoea. The three species exhibited similar lengths of cephalic structures, but S. olivacea had significantly shorter (P<0.05) abdominal structures. The duration of spawning from ablation was the shortest in S. tranquebarica and the longest in S. olivacea. The study is relevant to aquaculture and fisheries management of Scylla species.

The effects of removing or trimming the chelipeds at various molt stages on regeneration, molt interval (MI) and specific growth rate (SGR) were determined in mud crab Scylla serrata. These strategies in combination with provision of shelters and food were tested in relation to survival and growth. Hatchery-reared S. serrata juveniles (1.3–2.2 g body weight) in the postmolt, intermolt, and premolt stages were subjected to autotomy of two chelipeds, and trimming of dactylus and pollex. Intact crabs served as the control group. Interval from stocking to first molt was significantly longer in crabs autotomized at intermolt or premolt than in trimmed or intact crabs, but was similar to intact crabs when autotomy was done at postmolt. However, MI from first to second molts was longer compared to intact crabs when chelipeds were removed or trimmed at premolt. After the first molt, autotomy and not trimming caused significant decrease in SGR. The SGRs at the end of the test were similar to intact crabs (postmolt: 7.90 ± 0.39, intermolt: 5.64 ± 0.50) when trimming of chelipeds was done at postmolt (8.01 ± 0.75) or intermolt (4.38 ± 0.40). However, SGR was lower when premolt crabs were subjected to autotomy (4.11 ± 0.67) and trimming (5.29 ± 1.40) than when chelipeds were intact (9.45 ± 0.47). A two-factor experiment was conducted in the second phase where intermolt crabs with autotomized or trimmed chelipeds (factor A) were either fed or starved but provided with shelters or fed but without shelters (factor B). After 10 days, higher survival was obtained in crabs with autotomized (95.55 ± 2.94%) or trimmed chelipeds (93.33 ± 3.33%) than in intact crabs (73.33 ± 6.67%). Survival was not affected by factor B, but higher final mean body weights were attained in fed crabs with (0.78 ± 0.04 g) or without shelters (0.74 ± 0.04 g) than unfed ones (0.48 ± 0.04 g). A third experiment was conducted to verify these results. Crabs with trimmed or intact chelipeds were either fed or unfed. No shelters were provided. Crabs with trimmed chelipeds (88.57 ± 0%) had higher survival than intact crabs (59.76 ± 7.56%) regardless of whether they were fed or starved; and fed crabs (0.82 ± 0.04 g) had higher mean body weight than unfed crabs (0.61 ± 0.07 g) regardless of whether chelipeds were intact or trimmed. These results indicate that trimming or total removal of chelipeds are effective strategies in reducing cannibalism.

Hatchery-reared animals for stock enhancement should be competent to survive and grow at rates equivalent to those of wild conspecifics. However, morphological differences are often observed, and pre-conditioning steps may be required to improve the fitness of hatchery-reared juveniles prior to release. In the present study, hatchery-reared Scylla serrata juveniles were reared either individually (HR-solitary) or groups in tanks (HR-communal), the latter group being exposed to intraspecific competition and foraging for food. After 21 days, both groups were compared to similar size wild-caught juveniles in terms of morphometric measurements of carapace spination, abnormalities and carapace colouration. There were some limited significant differences between HR-communal crabs and HR-solitary crabs in terms of length of 8th and 9th lateral spines and in body-weight-carapace width ratio, but both treatments differed from wild crabs, which were heavier and had longer carapace spines for thei

Early instars of three mud crab Scylla species were reared in different salinities and survival and growth were compared. Scylla olivacea were reared in salinities of 12, 16, 20, 24, and 32 g/l (control). Scylla serrata and S. tranquebarica were reared in salinities of 8, 16, 20, 24, and 32 g/l (control) After 75 days, survival of S. olivacea and S. serrata was not affected by salinity but survival in S. tranquebarica was significantly higher in 8-20 g/l than in 24 and 32 g/l. The molt interval was shorter in S. olivacea, and more animals attained the fifth molt, than in the other species. The molt interval was shorter in 12-20 g/l than in 24 and 32 g/l for S. olivacea, did not vary among test salinities for S. serrata, and was shortest in 20 and 24 g/l in S. tranquebarica where fewer animals attained a fourth molt in 32 g/l than in 8-20 g/l. The molt increment was influenced by salinity only in S. olivacea. At the end of the test, all three species exhibited lower internal carapace width and mean body weights in 32 g/l. Among the three species, S. serrata was most versatile in tolerating a wide range of salinities during nursery culture.

Growth and feed efficiency were determined in red snapper, Lutjanus argentimaculatus (Forsskal 1775), fed diets containing L-ascorbyl-2-monophosphate-Mg (AMP). Fish (13.39±0.08 g) were fed a practical diet without vitamin C supplement for four weeks then stocked in twelve 650-l tanks at 30 fish/tank and fed one of four practical diets containing AMP at 0, 60, 180, or 540 mg/kg dry diet for 17 weeks. Survival rates in all treatments were similar (88.9-98.9%). Fish fed the 0 or 540 ppm diets had inferior final average weights, protein efficiency ratios, and feed conversion ratios than fish fed the 60 or 80 ppm diets (p<0.05). Growth of fish fed the 0 or 540 ppm diets slowed down on day 60 and fish fed the AMP-free diet exhibited clinical signs of vitamin C deficiency with a soft body and a significantly high (p<0.05) hepatosomatic index. Ascorbic acid in brain and liver tissues rose with the level of dietary AMP. Fish fed the 540 ppm diet had significantly lower hematocrit (p<0.05) than fish fed the 60 or 180 ppm diets. Histological analysis of the liver and kidney of fish fed the 180 and 540 ppm diets showed changes indicative of possible toxic effects. Based on growth, feed efficiency, tissue histology, and hematocrit level, AMP at 540 ppm is toxic to snapper. Thus, supplementation of 60 ppm AMP or its equivalent 26 ppm ascorbic acid in practical diets for red snapper promotes optimum growth and feed efficiency and prevents vitamin C deficiency symptoms.

Different aquaculture species such as finfishes and bivalves have been reported to control the luminous bacterial disease of shrimp, usually caused by Vibrio harveyi. The use of seaweeds in shrimp culture system has reportedly improved water quality and reduced the bacterial count. This study evaluated the potentials of two species of seaweeds, Gracilaria heteroclada (Ad Xia) and Kappaphycus striatum (Schnitz), to control the growth of V. harveyi. V. harveyi was inoculated into control tanks containing shrimps only and into treated tanks containing both shrimp and macroalgae. Luminous bacterial counts were monitored daily. From day 2 to day 6, luminous bacterial count in tanks with G. heteroclada was significantly lower than those in tanks with K. striatum. Bacteria isolated from the rearing water containing K. striatum and G. heteroclada and from the seaweed homogenized in sterile seawater showed anti-Vibrio harveyi activity. The seaweed homogenate per se also showed anti-luminous bacterial property. Presence of both G. heteroclada and K. striatum in shrimp culture system has the potential to control the growth of luminous bacteria. G. heteroclada was more efficient and sustainable, as shown by the lower luminous bacterial count and the higher percentage recovery of this macroalga after 11 d in experimental tanks.

Luminous bacterial disease caused by Vibrio harveyi has devasted the shrimp industry. The use of different strains of tilapia and other fish species polycultured with shrimp cultured at a salinity of 24 ppt to control luminous bacteria has been reported. These species, however, could not tolerate salinities higher than 24 ppt. Alternative species/strains that could be used to control luminous bacteria at high salinities need to be investigated. Likewise, the effect of fish size on the growth of luminous bacteria is worth studying. Shrimp (Penaeus monodon Fabricius) were stocked in concrete tanks filled with 34 ppt cartridge filtered seawater. Tanks were stocked with two sizes (16 pcs, average body weight (ABW) = 55 g and 6 pcs ABW=250 g) of the red tilapia hybrid Oreochromis mossambicus Peters x O. niloticus Linnaeus, except for the tanks that served as the control. Luminous bacteria (V. harveyi) were inoculated into the tank water to a density of 10⁴ Cfu mL^-1. Significantly lower luminous bacterial count was observed in tanks with either of the two sizes of red tilapia hybrid compared with the control, after 5-7 d. Bacteria isolated from the fish feces, mucus and rearing water; and the fish feces and mucus themselves demonstrated anti-V. harveyi activity. Results showed that the red tilapia hybrid could be used to control luminous bacteria at salinities as high as 34 ppt and that the size of the fish did not affect its efficiency. The ability of the red tilapia hybrid to control the growth of the luminous bacteria V. harveyi is attributed to different factors such as the mucus, the feces and the bacteria associated with tilapia culture. Bacteria associated with the fish mucus and feces also contributed to the anti-V. harveyi activity of these biological substances.

Growth of several genetically improved Nile tilapia (GIFT or Genetically Improved Farmed Tilapia, FaST or Freshwater Aquaculture Center Selected Tilapia, SEAFDEC-selected) and domesticated red tilapia (BFS or Binangonan Freshwater Station, NIFI-red or National Inland Fisheries Institute red, HL or Hacienda Luisita) stocks were compared in controlled (tank) and uncontrolled farm conditions (lake-based cages) with unselected NIFI or Chitralada Nile tilapia as control. Specific growth rate differed significantly (P = 0.009) in tank-reared Nile tilapia stocks where GIFT grew best at 1.358%/day followed by FaST (1.307%/day), control stock NIFI (1.257%/day) and SEAFDEC-selected (1.202%/day). Genetic effect explained 84.4% of the variance in growth of Nile tilapia in tanks. Although Nile tilapia growth in cages followed the same trend where GIFT grew best at 1.570%/day, no significant stock differences (P = 0.479) were noted. Meanwhile, red tilapia reared in either tanks or cages showed no significant stock differences in terms of growth. However, survival of the red tilapia stocks in cages differed significantly with HL having the highest percentage survival at 93.3%. The different growth responses of the Nile tilapia stocks especially under controlled (tank) farm conditions were largely due to genetic factors (stock differences).Under uncontrolled farm conditions, environmental factors were generally observed to have also affected the survival and to some extent, the growth of Asian Nile and red tilapia stocks.

Carposporophytes of the seaweed, Kappaphycus striatum, from the wild were made to shed spores in the laboratory and grown in multi-step culture method until they reached maturity. For each succeeding transfer onto increasingly bigger culture vessels, there was a marked increase in the growth of carposporelings. When plantlets were ready for outdoor culture, they were placed in aquaria and concrete tanks and later moved to the sea in net cage and long-line for grow-out culture. Successfully growing sporelings from carposporophytes in the laboratory until they reach market size seems to depend on the stage of sporelings and environmental factors such as photoperiod and temperature. In this study, carpospore progenies (diploids) also matured into tetrasporophytes and haploid progenies showed resistance to higher temperature.

The reduction of the survival of mud crab during culture has been largely attributed to aggressive encounters and cannibalism. In some crustaceans, suppressed aggression is linked to increased concentration of circulating and brain serotonin (5-hydroxytryptamine, 5-HT). Likewise, tryptophan (TRP), a precursor of 5-HT is reported to suppress the aggression and improve the survival of some cultured fish through dietary supplementation. We investigated the effects of feeding formulated diet with different TRP levels (0.32% as control, 0.5%, 0.75% and 1% of dry diet) on the agonistic behavior, growth and survival of juvenile mud crab Scylla serrata. Mud crabs were individually stocked and fed the experimental diets for 4 weeks before they were set to a one hour fight experiment. The fights were recorded using a video camera and the aggressiveness of the crabs was quantified. Hemolymph was sampled after 15 and 30 days of feeding (resting) and right after the fight to measure circulating 5-HT concentration. Higher TRP levels suppressed the aggressiveness of mud crab in a dose dependent manner. The intensity and frequency of attacks were both significantly lower (P < 0.05) in those given diets containing 0.75% and 1% TRP as compared with the control. Serotonin-ELISA assay revealed that 5-HT levels in the hemolymph before the fight (after 15 and 30 days; resting) were not significantly different between treatments. However after the fight, 5-HT concentration was significantly higher in TRP-supplemented mud crabs as compared with the control (0.5% = P < 0.05; 0.75% and 1% = P < 0.01). Furthermore, mud crabs (0.16 g BW) were reared in 0.40 m² circular tanks at 20 crabs/tank and fed the experimental diets for 30 days to determine growth and survival. Survival was higher in TRP-supplemented mud crabs (0.5% = 35%, 0.75% = 33.33%, 1% = 35%) as compared with the control (18.33%). However, daily growth gain (DRG), relative growth rate (RGR) and specific growth rate (SGR) were reduced in TRP-supplemented groups than with the control group. In conclusion, the data shows that the aggressive behavior of juvenile mud crab can be suppressed by supplementation of L-TRP. The survival of juvenile mud crab can be improved by increasing the level of TRP to 0.5%–1%. However, higher TRP levels may affect growth of mud crab. TRP supplementation resulted to a significant increase of 5-HT concentration in the hemolymph which was clearly observed after the fight suggesting that 5-HT plays an important role in suppressing the agonistic behavior of mud crab during aggressive encounters.