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.

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.

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.

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.

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.

From the introduction:

A series of management proposals were developed to ensure the continuation of the coconut crab on Niue. A summary of the recommendations follows:

1. No female coconut crabs with large orange-tinted abdomens or bearing external eggs to be taken or interfered with.
2. Introduction of a minimum legal hunting size of 36mm thoracic length for all coconut crabs (includes providing a size-guide for hunters to use in the field to size crabs).
3. Banning of all coconut crab exports.
4. Introduction of closed hunting seasons.
5. A comprehensive public awareness campaign (involving production of a large coconut crab conservation poster and educational video movie).
6. Establishment of formal coconut crab sanctuaries.
7. Banning use of dogs by coconut crab hunters.
8. Instigation of a coconut crab monitoring programme.
9. Preservation of coconut crab habitat.

Its large size (up to 1 metre) and land-based behaviours suggest Coconut Crab is a species with the potential for aquaculture, but there is very little published research available. It has been noted that wild populations of Coconut Crab are shrinking in the Cook Islands. H. H. Taylor, P. Greenaway, and S. Morris published a report (1993) in the Journal of Experimental Biology entitled Adaptations to a Terrestrial Existence by the Robber Crab Birgus latro – osmotic and ionic regulation on freshwater and saline drinking regimens.

Joan Martinez-Alier, from the Department of Economics and Economic History, Universitat Autònoma de Barcelona, Spain has published a report entitled Ecological Conflicts and Valuation – mangroves vs. shrimp in the late 1990s. From the abstract:

Shrimps are produced in two different ways. They are fished in the sea (sometimes at the cost of turtle destruction) or they are “farmed” in ponds in coastal areas. Such aquaculture is increasing around the world as shrimps become a valuable item of world trade. Mangrove forests are sacrificed for commercial shrimp farming. This paper considers the conflict between mangrove conservation and shrimp exports in different countries. Who has title to the mangroves, who wins and who loses in this tragedy of enclosures? Which languages of valuation are used by different actors in order to compare the increase in shrimp exports and the losses in livelihoods and in environmental services? The economic valuation of damages is only one of the possible languages of valuation which are relevant in practice. Who has the power to impose a particular language of valuation?

From the Introduction:

In many coastal areas of the tropical world, in Ecuador, Honduras, Sri Lanka, Thailand, Indonesia, India, Bangladesh, Philippines, Malaysia, there is social resistance against the introduction of shrimp farming for export, since this implies the uprooting of mangroves in order to build the ponds. In such areas, poor people live sustainably in or near the mangrove forests, by collecting shellfish, by fishing, by making use of mangrove wood for charcoal and building materials. The mangroves are usually public land in all countries, being in the tidal zone, but governments give private concessions for shrimp farming or the land is enclosed illegally by shrimp growers. Illegality is prevalent not only because of the public character of the land, but also because there are often specific environmental laws and court decisions protecting the mangroves as valuable ecosystems.

Shrimp or prawn production entails the uprooting of the mangroves, and the loss of livelihood of people living directly from, and also selling, mangrove products. Beyond direct human livelihood, other functions of mangroves are also lost, perhaps irreversibly, such as coastal defence against sea level rise, breeding grounds for fish, carbon sinks, repositories of biodiversity (e.g. genetic resources resistant to salinity), together with aesthetic values. Pollution from the shrimp ponds destroys the local fisheries. Also, wild shrimp disappear because of the loss of breeding grounds in mangroves and because they are overharvested as seed for the ponds.

Yabbies (Cherax albidus and Cherax destructor) are indigenous to central and eastern Australia and have received considerable aquacultural interest. Although some yabbies are produced from ponds on purpose-built farms, the vast majority of commercial yabbie production in Australia comes from trapping in farmers’ dams what are essentially wild yabbies. This use of existing farm dams originally built to water stock has enabled rapid expansion of the industry because of the low entry cost. The yabbie industry currently harvests around 4000 farm dams in Western Australia. The rapid growth experienced by the industry is expected to continue, with processors reporting an increase this year of up to 400% in the number of farmers harvesting yabbies.

Australian yabbies are in demand internationally due to their high quality, larger size than crayfish produced by overseas competitors, acceptance by European markets as a replacement for diminishing stocks of their own native crayfish, freedom from major diseases and ability to be landed live in the major international markets.

Research has been undertaken to develop better performing varieties – often unmanaged populations become stunted because of overpopulation. Quantum – ABC Television reported in 1999 about the development of cross-breeding yabbies to produce all male offspring.

Dr Ian W Purvis of the Australian Government’s Rural Industries Research and Development Corporation has published Breeding Bigger Yabbies – Developing a genetically improved yabby to facilitate farm enterprise diversification. From the summary:

Aims of the Research
The objective of the research was to establish the best wild strains for aquaculture by discovering the heritability of desired characteristics, such as fast growth and large meaty tails. These strains were then selectively bred to develop a strain of yabby better suited to aquaculture.

Once such a yabby exists in an aquaculture environment, the yabby farmer can better control growth and quality of the livestock, important factors to maintaining a reliable and continuing market for this product.

Methods Used
Superior performing broodstock yabbies, from various geographic populations, identified by a strain comparison trial were combined to create a new “commercial” strain and subjected to four generations of within family selection. Faster growth was the primary selection goal. At the beginning of the trial the program was based on the evaluation of 100 full siblings from each of 30 families. Poor survival of three families reduced the total number in the program to 27. A control line consisting of randomly bred individuals from the 30 families was also maintained to allow assessments of genetic gain to be made through selective breeding.

Results
Of the four generations of selection, significant differences in mean liveweight at harvest were observed between select and control lines. The difference represented an average response to selection in both sexes of 12% per generation and a realized heritability for liveweight of 30%.

These results demonstrate that response to selection for liveweight in the yabby, Cherax destructor, can be successfully achieved. By selecting within families, significant gains were achieved in generations F2 and F3 that averaged around 15%. Coupled with the initial gains achieved by selecting the F1 founder generation, the select animals in generation F3 grew at 60-70 % faster than the average of all strains taken from the wild to initiate this study.

The full report is available as a .pdf.

This is based on a number of advantages of this species over many other crustaceans. It adapts to a relatively wide range of temperature from a minimum of 15 to a maximum of 35°C. This species has a relatively short larval life. It is also a fast growing species. Fast growing individuals reach market size in about 7–8 months, and the meat is of high quality in terms of tests and texture.

Food is normally the largest single item in the running expenditure of a prawn hatchery or prawn farm. If prawns are held in artificial confinement where natural food are absent or limited, an external food source should be added. For example, the external food of freshwater prawn larvae that are held in tanks may consist of live food (nauplii of brine shrimp) or artificial food (fish egg, fish flesh, formulated feeds, etc.)

The production of freshwater prawn stocked in pond depends on the ability of the environment to produce natural food. Various factors such as soil and water fertility, water temperature and intensity of solar radiation affect the production level of natural food in the pond. However, for maximum rate of performance, the supplemental feeding programme is supposed to be important. Hence, the knowledge of nutrient requirements, the preparation of suitable feeds from the local available ingredients, feeding techniques, and the cost effectiveness of prepared feeds is of paramount importance to commercial success.

The FOA have published a free report from November 1986 (available online) on the Optimum Dietary Protein Requirement for Macrobrachium rosenbergii Juveniles, by Jocelyn L. Antiporda, a Research Associate from the Southeast Asian Fisheries Development Center (SEAFDEC – AQD), (Binangonan Research Station, Binangonan, Rizal Philippines 3106).

Abstract: The dietary protein requirement of M. rosenbergii juveniles was determined in growth trials performed in indoor aquaria using rations based on fish meal and shrimp meal as the main sources of protein. Five protein levels from 20 – 40% at 5% interval were tested to assess the best growth. Mean body weights and lengths of 4 replicate treatments were subjected to analyses of variance in determining differences between protein levels. Results showed no significant differences in all variables considered. Under this laboratory feeding experiment, the prawns attained weights of 0.95 g (994% gain), 0.94 g (921% gain), 1.3 g (1417% gain), 0.95 g (996% gain) and 1.17 g (1263% gain) for 20%, 25%, 30%, 35% and 49% crude protein levels, respectively in 89 day-culture period.

From the introduction:

One of the major factors limiting the economic success in any commercial culture of a species is the food requirement. Shang and Fujimura (1977) estimated feed cost to account for about 13 – 27% of the total annual cost of production. Protein, being an important dietary constituent among animals, directly influence the formulation of diets and consequently affect the cost of production. Accumulated knowledge on the nutrient requirements of the prawn is limited and the lack of standard techniques among researches resulted to wide variations of findings thereby making direct comparisons difficult. Most of the available data relating prawn growth and dietary protein levels have been reviewed by Forster (1976), New (1976) and Wickens (1976). Data on the nutritional requirements of M. rosenbergii are scarce. Several workers have tried to develop artificial diets capable of sustaining good growth using a variety of foodstuffs (Kanazawa, et al., 1970; Cowey and Forster, 1971; Deshimaru and Shegino, 1972; Sick et al., 1972; Andrews et al., 1972; Forster, 1972; Balazs et al., 1973). Studies by Weidenbach (1982) confirmed that prawns ingest commercial pellets when available and that prawns also utilize available vegetation regardless of the presence of commercial pellets. Among the foodstuffs used, flesh of molluscs and crustaceans were found the most acceptable, producing the best growth especially among the marine prawns (Deshimaru and Shegino, 1972; Forster and Beard, 1973). Deshimaru and Shegino (1972) stated that marine prawn growth correlates with the amount of crude protein in the diet and that diets having crude protein above 60% showed high feed efficiency as a rule.

The book is subtitled: ‘An introduction to the study of zoology’. I particularly enjoy the ‘kinder, gentler’ writing style and it feels (or perhaps more accurately – reads) as though Huxley is very attuned to a more holistic approach to describing the crayfish.

The online version is supported by the original elegant woodblock illustrations and, as well, Rich has created a glossary (which was not part of the orginial edition).