aquaculture

The Australian Centre for International Agricultural Research (ACIAR) is a statutory authority that operates as part of the Australian Government’s development cooperation programs. The Centre encourages Australia’s agricultural scientists to use their skills for the benefit of developing countries and Australia. Geoff Allan and Don Fielder (from ACIAR) have published a .pdf document for download entitled Mud Crab Aquaculture in Australia and Southeast Asia.

The summary:

Mud crab aquaculture has been practised for many years in Southeast Asia, based primarily on capture and fattening of juvenile crabs from the wild. There is an unmet demand for mud crabs and this has led to over-exploitation in many areas. Difficulties with obtaining wild caught juveniles for farming operations, plus concerns of further over-exploitation, have led to major investments in research into hatchery techniques. To review mud crab aquaculture in Australia and Southeast Asia, ACIAR funded a scoping study, followed by a workshop to review the study and discuss status and problems in different regions. Those results are presented in this report.

A.F. Medina Pizzali has published research via the FAO entitled Low-Cost Fish Retailing Equipment and Facilities in Large Urban Areas of Southeast Asia. Of particular interest from a mangrove crab perspective is a case study from metro Manila.

Four species of crabs are of commercial importance in Metro Manila; these are pelagic swimming crab (Portunus pelagicus), mangrove crab (Scylla serrata), peregrine crab (Varuna litterata) and horned ghost crab (Ocypode spp). Mangrove crabs are considered a delicacy and are always marketed alive. The Metro Manila market is characterised by consumer preference for live mangrove crabs which command high prices; in particular, ripe females fetch premium prices. The domestic market is supplied with mangrove crab the year-round, with a peak season from May to September. During the Christmas period, there is an increased demand and prices of live mangrove crab are relatively higher.

The FAO has published a document entitled ‘Farming Freshwater Prawns – A manual for the culture of the giant river prawn (Macrobrachium rosenbergii)‘ (2002).

From the abstract:

This manual provides information on the farming of Macrobrachium rosenbergii. Many of the techniques described are also applicable to other species of freshwater prawns that are being cultured. The manual is not a scientific text but is intended to be a practical guide to in-hatchery and on-farm management. The target audience is therefore principally farmers and extension workers. However, it is also hoped that, like the previous manual on this topic, it will be useful for lecturers and students alike in universities and other institutes that provide training in aquaculture.

After a preliminary section on the biology of freshwater prawns, the manual covers site selection for hatcheries, nurseries and grow-out facilities, and the management of the broodstock, hatchery, nursery and grow-out phases of rearing. Harvesting and post-harvest handling are also covered and there are some notes on marketing freshwater prawns. The reference and bibliography section is generally restricted to a list of relevant reviews, as well as other (mainly FAO) manuals on general aquaculture themes, such as water and soil management, topography, pond construction and simple economics. Every attempt has been made to illustrate the management principles described in this manual by photographs and drawings. The manual contains many annexes on specific topics, such as the production of larval feeds, size variation and stock estimation. The final annex is a glossary; this lists not only terms used in the manual itself but also terms which the readers may find in other documents that they may consult.

The Culture and Management of Scylla Species (CAMS) project was a collaboration among four institutions worldwide – the University of Wales (Bangor) in the United Kingdom, Artemia Reference Center of the University of Ghent in Belgium, Can Tho University in Vietnam, and SEAFDEC/AQD in the Philippines. The CAMS project has reported on disease control and management projects in the Philippines and Vietnam. The objective: To improve the reliability and sustainability of crab hatchery systems through the use of probiotic bacteria as an alternative to microbials in disease control. The reports from the Philippines and from the Vietnamese research are available online. From the introduction:

For 2002 and 2003, monitoring activity of problems in large-scale hatchery rearing of crab larvae was done to identify windows of opportunity for probiotic application. These led to identification of various microbial fouling and disease-causing organisms in spawned eggs and hatchery-reared larvae.

Celia R. Lavilla-Pitogo and Leobert D. de la Pena, from the Aquaculture Department, Southeast Asian Fisheries Development Center Tigbauan, Iloilo, Philippines; published a report (December 2004) entitled Diseases in Farmed Mud Crabs Scylla spp.: Diagnosis, Prevention, and Control. From the forward:

Aquaculture production has suffered many set-backs due to the occurrence of diseases. Many of the diseases are caused by infectious organisms that are difficult to detect and need sophisticated instruments for diagnosis, but most disease occurrence and mortality in farmed aquatic animals are related to poor rearing water quality. It is, therefore, important for technicians and farmers to recognize the relationship between the animals they culture and the aquatic environment. The Government of Japan, through the Regional Fish Disease Project, funded research on diseases affecting mud crabs in order to come up with sound prevention and control methods.

This book is a collection of observations gathered from various research and commercial culture activities, and gives emphasis on disease recognition using simple techniques and gross observations of affected crabs. However, since many of the diseases are caused by microorganisms, microscopy is an important technique for their diagnosis. The authors of the book encourage active cooperation between farmers and diagnostic laboratories for disease identification, prevention, and control in order to build up more information to increase production. The Regional Fish Disease Project supports sustainable mud crab production and hopes that farmers and other users of this book will attain their production goals.

The report is located within a framed web site. Chapter 1 includes information about diseases in eggs and larvae. Chapter 2 includes information about diseases in juveniles and adults. The appendix includes documentation of various microscopy techniques. There is also a glossary.

A great deal of research into mud crab husbandry at academic levels and at more grassroot levels has been undertake in the Philippines. Esperanza A. Santos and Leah Charito T. Tambolero have written about a Bureau of Fisheries and Aquatic Resources – Fisheries Resource Management Project entitled Reviving a Coop: Rising Above Waters Through Mangrove Crab Culture. The coop also raised tilapia and prawns as secondary stocks. The authors report report: ‘After a full year implementation, the project provided substantial earnings for all the members of the coop. They hope that their learnings will be valuable lessons as well for those areas, families and people’s organizations interested to venture into mangrove crab culture.’

The Science and Development Network sumarises, and the New Agriculturalist reports on research to more closely integrate crab culture with sustainable mangrove management. From the introduction:

The rapid spread of aquaculture in recent decades has brought riches to some, ruin to many, exclusion to the poorest coastal dwellers, and environmental degradation. Scientists in the Philippines are adapting aquaculture to make it sustainable over the long term and suitable for small-scale, family-level operators. An innovative system of captive crab culture in live mangrove is being developed in the central Philippines and is now being verified and demonstrated on the southern island of Mindanao.

The Culture and Management of Scylla Species (CAMS) project was a collaboration among four institutions worldwide – the University of Wales (Bangor) in the United Kingdom, Artemia Reference Center of the University of Ghent in Belgium, Can Tho University in Vietnam, and SEAFDEC/AQD in the Philippines. The CAMS project has reported on aquasilviculture projects in the Philippines and Vietnam. The objective: To refine systems for integrated aquasilviculture of mud crabs within mangroves, specifically by reducing fish biomass requirement through low cost incomplete feeds and utilization of natural productivity. The aquasilviculture reports are available online.

Mud crabs, Scylla spp., also known as mangrove crabs, occur naturally in association with mangrove swamps and nearby intertidal and subtidal muddy habitats. Mud crabs can exceed 3kg in body weight, yielding high volumes of delicate flavoured meat and are accordingly sought after as a quality food item. Easily caught with simple traps or nets, they remain alive for considerable periods after capture and they are highly valued as an important income source for small-scale fishers throughout the Asia-Pacific region.

Scylla spp. seem to adapt to an aquaculture regime reasonably well, and they have been cultured in China for at least 100 years, and throughout the rest of the region for decades. In Japan, sea-ranching of hatchery reared mud crab seed has been employed but seed production has not proved reliable. Almost all crab aquaculture production relies on wild-caught stock, as larval rearing has not yet reached a commercially viable level for stocking into aquaculture farms. Megumi Minagawa, Takeshi Hayashibara, Motohiko Sano, Motoya Tamaki, Kouki Fukuoka, and Katsuyuki Hamasaki, from the Seikai National Fisheries Research Institute, have published a brief report (in English) entitled Habitat characters of juvenile mud crab, Scylla serrata.

In Australia, Clive P. Keenan, from the Bribie Island Aquaculture Research Center, has published a report entitled Aquaculture of the Mud Crab, Genus Scylla – Past, Present and Future. From the abstract:

Crabs of the genus Scylla are strongly associated with mangrove areas throughout the Pacific and Indian oceans and form the basis of substantial fishery and aquaculture operations. Aquaculture production currently relies on wild-caught seed for stocking ponds, as larval rearing at a commercial scale is still difficult. One of the major problems for effective mud crab management and aquaculture is the likelihood that there are a number of genetically distinct species. Research has demonstrated the presence of at least four distinct species. Laboratory experiments of the larval stages of each species should provide valuable information on each species’ biological and ecological requirements. There are two basic forms of land-based mud crab aquaculture: fattening of crabs with a low flesh content, and grow-out of juveniles to market size. Fattening is a very profitable activity, employing high densities of crabs and low costs. However, total production is low because of mortalities due to cannibalism. Grow-out systems for mud crabs show much more variety and production can be very high. Grow-out systems are usually pond-based, with or without mangroves, although intertidal pens can also be used. Without mangroves, lower stocking rates provide the best return. In shallow mangrove ponds, there are two distinct forms of aquaculture: (i) intensive, with higher stocking rates and supplemental feeding; and (ii) extensive, in large mangrove silviculture ponds where the stocking rate is very low, and no supplemental feeding is involved. Growth rates under all systems are comparable, with production of commercial-sized crabs three to four months after stocking with seed crabs. Further research is required into the habitat preferences of each species so that production techniques can be modified to suit their respective requirements. With advances in the hatchery production of mud crab juveniles for stocking into ponds and enclosures, the future of mud crab aquaculture looks promising.