The binding capacity of six natural and eight synthetic feed binders were tested in a basal diet formulated for the mud crab. Incorporation levels of natural binders ranged from 1 to 25% while those of synthetic binders ranged from 0.1 to 5% and these were tested for pellet stability in seawater by a) 10-min immersion, and b) at different time intervals. Pellets with synthetic binders were more water-stable than pellets with natural binders. Three synthetic binders and natural binders (glutinous rice starch and carrageenan + CMC) showed best results. The Apparent Digestibility Coefficients (ADC) of crude protein (ADCCP) and crude fat (ADCCFt) of the basal diet were determined when selected feed binders were included in the formulation. These were determined by using an inert indicator, chromic oxide. Results showed that the ADCCP and ADCCFt of the basal diet were not similar when different binders were used, and these differences ranged from 3 to 7%. Carrageenan combined with a synthetic binder improved ADCCP and CDCCFt values.

The effect of feeding different ratios of natural food to formulated feed on the production and profitability of Phases 1 and 2 of nursery culture (3 weeks per phase) of hatchery-produced crab Scylla serrata was investigated. The feeds consisted of: mussel meat (M) alone, formulated diet (FD) alone, and their combination at M:FD ratios of 5 : 95, 10 : 90, 15 : 85, 20 : 80, 25 : 75 and 30 : 70. The crabs were stocked randomly in 12-m² net cages installed in the nursery pond at stocking density of 50 m^-2 for Phase 1 and 10 m^-2 for Phase 2. Crabs were fed three times daily at 0830, 1300 and 1630 h. Results showed that in both phases, the survival rate, body weight, carapace width, and feed conversion ratio of crabs fed M, FD, and combination at different ratios were not significantly different (p>0.05). Profitability was better in 15 M:85 FD or 20 M :80 FD (Phase 1) and 30 M:70 FD ratio (Phase 2). The use of complete formulated diet as feed for crabs reduced the reliance on wet natural food.

The socio-economic implications of technology transfer of mud crab culture on small-scale growers in Northern Samar and the mechanism of nursery technology transfer were investigated. The study covered four Peoples Organizations (POs), each operating in villages of the four municipalities of Northern Samar namely, Lavezares, Rosario, Laoang, and Pambujan. These were sites of the Philippine-Australian Community Assistance Program - assisted mud crab (Scylla) culture livelihood projects. Interviews from 60 beneficiaries revealed that most (76%) were relatively new to mud crab culture, particularly fattening or growout, but 65% were gleaners of mud crabs for more than 5 years. The average age of respondents was 45 years old and were predominantly male. Most (93%) were married with an average household size of six. A cost and return analysis of mud crab fattening in pens using only two compartments showed that the net income (P4,832/month for a 30-day culture period) is not sufficient if shared among 40 PO members participating in only one economic activity. Consequently, most (63 %) respondents whose livelihood projects were cooperative undertaking were no longer keen with the cooperative-run project. Interestingly, those (83 %) who operated their own farm wanted to continue and expand (26 %), particularly those in Rosario. The motivation factors that influenced growers to continue mud crab culture and adopt the nursery technology being disseminated were primarily economic with extra income and source of cash as main reasons for adoption. Majority also claimed that the nursery technology that was being transferred by SEAFDEC/AQD was simple. The mud crab pond nursery technology transfer involved community training and participation of beneficiaries, beginning with the linking of technologists and socio-economists with on-the-ground partners. Thereafter, season-long training and farm demonstration followed comprising lecture series and hands-on demonstration. Nursery pond operations were conducted in an open pond (Rosario) and in a pond within a mangrove area (Pambujan). Survival in the pond within a mangrove area was higher (68 %) than in an open pond (50 %) for phase 1, suggesting that the mangrove played a role on mud crab endurance. However, survival in phase 2 (72 %, Pambujan; 83 %, Rosario) showed a reversed trend, suggesting that bigger crablets can withstand/endure harsh pond conditions. Results of the demonstration indicated that the nursery technology is a viable enterprise, showing an ROI of 93.50% in Rosario and 198.04% in Pambujan. Most (83%) of the growers were interested in the nursery technology, although only few PO members participated in the season-long training. Ownership of area, market, and farm distance from household were the more important considerations that influenced small-scale growers in adopting the technology.

Mangroves are known as important nurseries for different species of fish and shellfish. In the Philippines, mud crabs Scylla spp. are among the most valuable crustaceans harvested from the mangroves and are considered a delicacy. However, varying levels of overfishing have been reported in different parts of the country. The decrease in production may be due to increasing demand for the resource and the loss of mangrove habitat. This problem may be addressed through regulation of fishing effort, rehabilitation of habitats, mangrove-friendly aquaculture and enhancement of wild crab stocks. This study shows the effect of mangrove rehabilitation on mud crab population. From July 2010 to December 2011, a total of 2.166 tons of mud crabs (n=17,558) have been collected from a 66.5 ha abandoned pond that has been recolonized by mangroves. The catch was dominated by S. olivacea (79.96%), then S. tranquebarica (19.92%) and S. serrata (0.12%). Male to female ratio was at 1.09:1. Individual daily yield ranged from 0.06 to 8.4 kg while catch per unit effort in terms of quantity and biomass ranged 0.02-1.46 crab gear^-1 day^-1 and 1.1-213.54 g gear^-1 day^-1, respectively. The results showed that mud crab population in this study site was much higher than the population in the reforested (Walton et al., 2006, 2007) and natural mangroves (Lebata et al., 2007) with almost the same area. For 18 months of sampling (April 2002-September 2003), only 3,924 crabs were sampled in the natural mangroves while 10,504 in the reforested mangroves. Mud crab production in the present study site resulted in a yield of 21 kg ha^-1 yr^-1, 5 and 3 times higher than the yield reported in the natural and reforested mangrove areas, respectively. These results imply that habitat restoration can be very effective in restoring natural populations of mud crab.

Development of economically viable techniques for growing hatchery-reared juvenile crabs to suitable sizes will address the problem on the source of seed stocks for soft-shell crab farming. This paper reports the production of hatchery-reared mud crab Scylla serrata from juveniles in the nursery to 73-106 g body weight (BW) crabs in the grow-out pond for the individual system soft-shell crab farming. Likewise, the performance of hatchery-reared S. serrata, and wild S. tranquebarica and S. olivacea juveniles was determined in the soft-shell crab production set-up. The BW increased from 1.8-1.9 g to 78-113.7 g when stocked at 0.5 ind m^-2 and from 1.6-2.3 g to 73-106.7 g at 1.0 ind m^-2 after 75 days. Growth rates at both stocking densities were comparable. However, survival was significantly higher (P<0.05) in lower (63.6~c1.01%) than in higher (35.6~c3.34%) stocking density. Male S. serrata (46.0 ~c 1.75%) had significantly higher BW increase than females (39.4 ~c 2.05%). Crabs stocked at sizes of 51-60 g showed significantly greater percent increase in BW (43.26~c 0.98%) compared with those at 61-70 g (40.98~c1.33%), 71-80 g (38.55~c 1.04%), 81-90 g (36.34 ~c 1.27%) and 91-100 g (38.52 ~c 1.67%). Among the three species, hatchery-reared S. serrata (42.14 ~c 1.34%) had significantly higher mean percent BW increase compared with S. olivacea (38.23 ~c 0.49%) and S. tranquebarica (36.16 ~c 0.78%). S. serrata had significantly shorter mean culture period (24.11 ~c 0.95 days) than S. tranquebarica (28.48 ~c 0.54 days) and S. olivacea (28.75 ~c 0.34 days).

Non-specific immune activitation is considered a potential prophylactic approach in the prevention of disease outbreaks in crustacean aquaculture. The present investigation evaluates the dietary supplementation of bacterial and algal derived immunostimulants including peptidoglycan, ergosan, mannan oligosaccharide and acidic polysaccharides from Ulva, Sargassum and Padina to enhance the immunological responses and resistance of Scylla serrata juveniles against white spot syndrome virus (WSSV) infection. Each of the test immunostimulant was optimized for dose and frequency of administration. Results showed significant enhancement of shrimp survival against WSSV infection if Mannan oligosaccharide is supplemented at 2000 mg kg^-1 diet applied every 3 days. Optimum dose and frequency of application for peptidoglycan was determined as 1000 mg kg-1 diet applied every 3 days while a dose of 2000 mg kg^-1 diet applied every 3 days was found optimum for ergosan. Enhancement of survival was also observed in crabs given the acidic polysaccharide extracts from seaweeds. Better survival was observed in the treatment receiving Ulva at 1000 mg kg^-1 applied every 3 days. Similar dose and frequency were also observed to enhance the resistance of the juvenile crabs against WSSV when maintained with diets supplemented with Padina and Sargassum acidic polysaccharides. The high survival in these treatments is associated with the prominent enhancement of immunological responses including phenol oxidase activity, respiratory burst and total hemocyte counts. At optimum dosage and application frequency, these immunostimulants are observed to improve overall growth performance of the juvenile crab. These results suggest that dietary supplementation of peptidoglycan, ergosan mannan oligosaccharide, and acidic polysaccharides from Ulva, Sargassum and Padina at a dose described above can be used to boost the immunological response and enhance the resistance of S. serrata juveniles against WSSV infection.

Studies were conducted towards the pilot scale production of stable and nutritionally adequate pellets suitable for mud crab Scylla serrata to help in efforts to increase mud crab production in the Philippines. Preliminary studies showed that mud crabs preferred pellets which were spherical or cylindrical and contained marine based attractants. Two practical diets were formulated and prepared in the Pilot Feed Mill of SEAFDEC/AQD. The extruded diets, along with a commercial mud crab grow-out diet, were subjected to proximate and Ca/P analyses as well as cholesterol analysis and water stability tests. The diets were fed to crabs in a controlled laboratory experiment using fiberglass tanks with flow-through, aerated seawater, and monitored from initial molt (M0) up to the second molt (M2). Tests revealed that the crabs fed Diet 1 (CP 48.28 %, CF 7.74 %, Ca 5.23%, P 12.93 %, cholesterol 0.173 %) showed the highest growth and better survival than those fed Diet 2 or commercial diet. Crabs fed Diet 1 took a shorter time to attain two molt cycles from M0. Survival was 70% after M2. Diet 1 was water stable within two hours. Abnormalities were observed including absent swimming legs or chelae, exposed gills, sores on exoskeleton, incomplete molting, or soft exoskeleton, but none that could be directly attributed to a specific treatment. Incomplete molting and slow hardening of the exoskeleton in crabs that accounted for the mortalities could be due to the low cholesterol levels in the diets especially in the commercial diet which had the lowest cholesterol level. Cholesterol supplementation of the artificial diet would be needed to improve molting success and survival of mud crabs in grow-out culture. The results of these experiments will be used to formulate a cost-effective grow-out diet for mud crab (supported by DOST-PCAARRD Grant in Aid).

Marphysa mossambica is commonly found in brackishwater ponds and is an important natural food for cultured stocks particularly mud crabs. To understand the burrowing activity of polychaete, survival and capacity to bioremediate pond sediments, tank experiments were conducted. In a completely randomized design with three replicates per treatment, small (1-month old, 28 mg) and large (3-month old, 139 mg) hatchery-bred M. mossambica were reared in two sediment types for 30 days without feeding. Aeration was supplied and water change was done every other day. Polychaete-free sediments served as control. Sediments obtained from SEAFDEC/AQD Dumangas Brackishwater Station were sun-dried, ground and passed through 1-mm sieve. Initial sediment A had 1.86% organic matter, 1,171 ppm available sulfur (SO₄^2-), 194.23 ppm iron (Fe) and 7.86 pH while initial sediment B contained higher organic matter (4.1%), available sulfur (2,456.67 ppm), similar iron level (199.34 ppm) and was more acidic (4.91 pH). In sediment A, small and large polychaetes did not differ (p>0.05) with the control in reducing organic matter but both significantly reduced (p<0.05) available sulfur (77-73%) and iron (69-71%). However, only the large polychaetes increased the pH (p< 0.05, 2.67%). In sediment B, only the large polychaetes reduced (p<0.05) organic matter (27%) but both small and large polychaetes significantly reduced (p<0.05) available sulfur (64-70%) and iron (70-74%). The pH increase was similar to control (17-24%). Large polychaetes had higher survival (93%, p<0.05) than small polychaetes (60%) in sediment B but not different (p>0.05) in sediment A (97%, 87%). The study demonstrated the bioremediation capacity of M. mossambica particularly in reducing available sulfur and iron in sediments.

Mud crab aquaculture industry in the province of Capiz received much attention after production constraints due to diseases were encountered by the prawn industry. Fishpond operators sought for an alternative high value species and realized the potential of the king crab, Scylla serrata. This species is not native to Capiz and has to be sourced from other parts of the country, particularly from the Bicol region and Samar. The techniques for grow-out culture were gradually refined as farmers learned from the experiences of others. Presently, mud crab aquaculture is being done by private sectors based more on art. However, mud crab culture requires a lot of science to make the production consistent and sustainable. The practices of farmers and the problems they have encountered are presented together with the overall industry concerns.