Southeast Asian Fisheries Development Center
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Genetic diversity and stock delineation of Philippine populations of the orange mud crab, Scylla olivacea
Get PDFAbstract only.The orange mud crab, Scylla olivacea, is regarded as an important fishery resource due to high demand and high market value. However, mud crab populations are threatened by over exploitation and habitat degradation, and would benefit from resource management interventions. The study examined patterns of genetic diversity and connectivity of orange mud crab populations across the Philippines, with the aim of identifying putative management units. A total of 387 Scylla olivacea were collected from ten localities across the Philippine archipelago. Phylogenetic analysis of mitochondrial control region (mtDNA-CR) DNA sequences revealed cryptic diversity among Scylla olivacea specimens with four mitochondrial lineages recovered. Analysis of molecular variance revealed that Philippine populations do not constitute a single genetic stock (0ST=0.00262; P=0.00015). Thirteen microsatellite loci were also utilized as additional markers to infer population structure and estimate genetic variation. Overall, S. olivacea populations exhibit high haplotype diversity (mean h=0.9803) and nucleotide diversity (mean ~p3.46%), which may be indicative of a large, stable population within Philippine archipelagic waters. This study provides information on genetic diversity and population structure of S. olivacea, which will be useful towards developing management and conservation strategies for sustainable development of natural S. olivacea populations in the Philippines
Nursery and grow-out feeding management of mud crab farmers in the Philippines: Santeh experience
No full textAbstract only.Mud crab (Scylla serrata) farming has been one of the means of livelihood of many Filipino farmers in coastal areas, specifically in Southern Luzon and Visayas. Nursery and grow-out operations in these areas vary in terms of their feeding management and techniques for a better yield. Farmers in Bicol region, specifically Sorsogon which is one of the sources of wild crablets in the country, are presently using pelleted feeds for nursing different crab sizes. On the other hand, farmers in Quezon, Bataan, Masbate, Negros and Capiz are growing crabs to marketable size for domestic and export markets.
It was noted that there are still farmers in some areas that use low value fish for feeding crabs resulting in the deterioration of the pond bottom and water environment. On the other hand, pelleted feeds serve as an alternative feed that addresses the problem of the declining supply of trash fish, corn, mussel and snails. The price of trash fish has increased significantly due to its unavailability in several areas. In addition, pollution of the water environment and fluctuations in the water parameters for crabs due to improper pond preparation, pollution and climate change have added stress to the crabs
Handling, storage and transport conditions of mud crabs in trading centers
Get PDFAbstract only.This study aims to improve the handling, storage and transport conditions of mud crabs. The usual practice of the crab growers in the Philippines is to bring the market size crabs to middlemen, brokers or operators of small trading centers immediately after harvest; then the crabs are brought to municipal traders or operators of bigger buying station. The crabs are sent to the exporters in Manila or Cebu. The crabs are exported mostly to Singapore, Taiwan, Hongkong and mainland China. The crabs are classified based on the species, body weight, sex, gonad maturity and intactness of limbs. Crabs are rejected for export when they are soft-shelled, very lean, or have incomplete limbs and abnormalities. Crabs with emaciated muscle (‘hagas’), ammoniacal odor (strong urine-like smell) and in an undesirable state are also rejected.
This paper presents the initial results of the project on the Improvement in the handling, storage and transport of mud crabs under Sub-program C entitled Improvement of Feeds and Stock Management Practices in Mud Crab Grow-out Culture under the National Mud Crab Science and Technology Program. It also presents issues and concerns on the present practices, and presents possible recommendations
Enhancing mud crab population through mangrove restoration
Get PDFAbstract only.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
Luminous Vibrio and the greenwater culture of the tiger shrimp Penaeus monodon with tilapia
No full textLuminous vibriosis is a devastating infection of penaeid shrimp larvae and juveniles causing heavy mortalities. To counter the bacterial pathogen, Vibrio harveyi, shrimp farmers in the Philippines modified their growout culture method of the black tiger shrimp, Penaeus monodon, juveniles and developed the greenwater culture technique. This culture method involves the use of pond water of all-male, saline-tolerant Oreochromis hornorum as rearing water for the culture of shrimp juveniles in ponds. Such a modified culture of P. monodon juveniles was found effective in preventing the onset of luminous vibriosis. Basic studies revealed that antiluminous Vibrio factors are inherent in the bacterial, fungal, and microalgal flora of the tilapia water, dermal mucus, and gut that singly or collectively inhibit the growth of V. harveyi, in vitro. The skin mucus studies of other brackishwater fish species showed that the siganids, Siganus guttatus, and red hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus), as well as sea bass, Lates calcarifer, are promising alternative fish species for this novel shrimp culture method. A review of pond-simulated studies in tanks and ponds, similarly, confirmed these findings and the impact of the greenwater culture technique on water quality, including its economic benefits to the farmer. The greenwater culture of shrimp can sustain the successful production of shrimp juveniles by inhibition of the luminous Vibrio. This culture method is also currently used in the growout culture of the white shrimp, Litopenaeus vannamei
Sensory systems and feeding behaviour of the giant freshwater prawn, Macrobrachium rosenbergii, and the marine whiteleg shrimp, Litopenaeus vannamei
No full textInformation on the sensory basis of shrimp feeding provides the means for assessment of the effectiveness of food items in terms of smell, taste, size, and colour. This chapter summarizes information about the sensory basis of the feeding behaviour of the giant freshwater prawn (Macrobrachium rosenbergii) and the marine whiteleg shrimp (Litopenaeus vannamei). Existing literature on these shrimp species and other decapod crustaceans is reviewed, and unpublished experiments using the selective sensory ablation technique to determine the involvement of vision, chemoreception, and touch sense in the feeding behavior of the juveniles of M. rosenbergii and L. vannamei are also described. To determine the role of vision in feeding, the eyes of the juveniles were painted over (deprived of vision) with white manicure and their feeding response to commercial pellets was compared with those with untreated eyes. The untreated eyed juveniles detected and approached a feed pellet right away, but the specimens blinded by the coating detected a pellet only after random accidental touch with the walking legs while roaming on the aquarium bottom. Juveniles that had learned to feed on pellets showed food search and manipulation responses to a pellet-like pebble without smell and taste. The early larvae (zoeae) of M. rosenbergii already have colour vision (that likely persists through life) and colour preference for blue and white. The adults of L. vannamei discriminated a blue-colored well among seven grey wells in a palette, also showing colour vision in this shrimp. A behavioural experiment with dyed prawn flesh showed that L. vannamei has innate color preference for yellow food over black, red, green, and blue food regardless of the background colours of the aquarium bottom. To disrupt chemoreception, the juveniles of both the species were abruptly transferred to water of drastically different salinity and the osmotic ablation destroyed the chemosensitive sensilla. The osmotically ablated juveniles approached a pellet right away but failed to ingest it; they had learned the visual cue and texture of the pellets and recognized them by vision and tactile sense. To determine the role of sensory appendages in feeding of L. vannamei juveniles, the antennal flagella, antennular flagella, and the pincers of the pereiopods were ablated. The ablated juveniles roamed the bottom, touched a pellet at random, grabbed it with the maxillipeds, and ingested it. Subsequently they learned to lower the head, actively swim forward, sweep the bottom with the maxillipeds, detect a pellet, and ingest it—thus indicating a plasticity in feeding behaviour in L. vannamei
Recent developments and enhancing transfer of the nursery technology for the mud crab Scylla serrata
No full textThe development of hatchery techniques for seed production of mud crab is expected to address the present problem on the depletion of wild seedstock supply for stocking in grow-out ponds. The nursery serves as the link between the two phases of culture as this involves growing of juvenile crabs produced in the hatchery to sizes that are suitable for stocking in the ponds.
Nursery rearing involves the use of net cages installed in ponds as holding system for ease in harvest and retrieval of crabs. In the first nursery phase, 0.3-0.5 cm carapace width (CW) juvenile crabs are reared to 1.5-2.0 cm CW for 3-4 weeks and stocks are harvested for selling or are grown further in a second nursery phase in which crabs reach 2.5-3.0 cm after another 3-4 weeks. This paper includes a review of techniques initially developed for the nursery and more recent refinements which involve the use of higher crab instar densities, provision of suitable shelters, trimming of claws and sorting. In addition, production results in farms of collaborators are presented to highlight the efficiency of dissemination and also discusses the challenges faced by the potential nursery industry
Initiatives on mud crab culture at the Palawan Aquaculture Corporation
Get PDFAbstract only.Mud crab (Scylla spp) has long been a prime commodity in both local and global market and is regarded as one of the important high-value crustacean species produced in the Philippines. Decades ago, its culture basically relied on the availability of wild seedstock collected and grown to marketable size, or on wild lean adult crabs that were fattened for a short period.
Developments and refinements in the hatchery and nursery techniques paved the way to bringing up culture activities to commercial levels. The Palawan Aquaculture Corporation embarked on mud crab culture in the mid 2014 where initial trials started. Collaboration with SEAFDEC/AQD was later forged bringing forth improvements in the hatchery, nursery and grow-out culture. Hatchery-reared juvenile crabs are now being sold