Sea Cucumbers as a Global Trade Commodity

Sea cucumbers, once dried and processed into bêche-demer, are a globally important trade commodity. Exploitation was initiated over 1000 years ago in Southeast Asia by Chinese traders, who encouraged coastal communities to collect the large, thick body-walled species of sea cucumbers and taught how to process them into bêche-de-mer (Conand 1990). Sea cucumbers are an ideal fishery resource and trade commodity: collection and processing methods are straightforward, requiring no specialized skill or equipment and, once processed, bêche-de-mer has a shelf life of many years. Historically sea cucumbers were exploited opportunistically as part of a multi-species fishery because, once processed, they could be stockpiled until traders passed through the region.

Sea cucumbers are a traditional delicacy prized by Chinese and other Asian consumers for their dietary and curative properties (Conand 1990, Purcell 2010). In the international seafood trade, sea cucumbers are regarded as a specialty product that falls within the same niche market as other high-value luxury seafood products, including shark fin, fish maw and abalone (Fig. 1). Considered a delicacy and seen as a sign of prosperity, sea cucumbers are not a staple of the Chinese diet; rather, they are consumed at festivals, special occasions and banquets. Given recent increases in disposable income, demand by middle and lower income groups has increased, although additional factors are concomitantly reducing demand, such as decreasing family size and rising prices (Ferdhouse 2004).

Global Sea Cucumber Fisheries

Sea cucumbers are now exploited in 70 countries around the world in industrial, semi-industrial and small-scale fisheries that stretch from polar to temperate and tropical zones (Purcell et al. 2012). The expansion of trade and the rise in demand for bêchede- mer in the latter part of the twentieth century led to widespread over-exploitation of sea cucumber stocks and the collapse of some fisheries. In tropical small-scale fisheries, overexploitation has been accompanied by a number of warning signs, such as use of illegal fishing techniques and collection of juveniles. In the majority of cases, management has been lacking and compliance insufficient to reverse the trends. The only countries that have a history of operating sea cucumber fisheries in a sustainable manner are essentially the main consumers - China, Japan, Korea and Taiwan. The key to their success lies in aquaculture. While these countries have always managed wild stocks prudently, ensuring that fishing grounds are re-stocked through the release of hatchery-reared seed, aquaculture has progressed at such a pace in China that annual aquaculture production of the temperate species Apostichopus japonicus currently exceeds 90,000 t, surpassing production from capture fisheries.

The Sandfish Holothuria scabra

This article explores efforts to culture the commercially valuable tropical sea cucumber, Holothuria scabra. This species, commonly known as sandfish, is one of the highest-value sea cucumbers exploited in the tropical Indo-Pacific fishery, with current prices ranging from US$110-200/kg (InfoFish SA 2010). Of all tropical species, sandfish are considered the best candidate for aquaculture, primarily due to the ease of access to its habitat, shallow nearshore seagrass beds. Other attributes include its relatively sedentary nature, meaning that sandfish can be ranched or reared in sea pens, the fact that they feed at a low trophic level, consuming organic matter and detritus, requiring no additional feed, and their relatively rapid growth, with hatchery-reared juveniles reaching market size within 12 months (Battaglene et al. 1999, James 1999).

Development of Sandfish Aquaculture

Research into sandfish aquaculture was initiated by Dr. D.B. James at the Tuitcorin Research Institute of the CMFRI in India in 1988 (James 1999). A decade later, the research thread was picked up by the WorldFish Center, which ran successive research programs in the Solomon Islands (1997-2000), New Caledonia (2001-2008) and Vietnam (2003-present; Battaglene 1999, Pitt and Duy 2004, Agudo 2006). This research led to the successful development and dissemination of hatchery, nursery and grow-out technology, which is currently being implemented by a number of other agencies and research groups around the world. In this article, an overview of hatchery and nursery technology is presented, together with recent simplifications that have been developed to customize the technology to low-investment systems in developing countries (Duy 2010, Gamboa et al. 2012, Mills et al. 2012).

Hatchery Production

Sandfish are broadcast spawners with separate sexes. Adults reach sexual maturity at a minimum size of 180 g (Agudo 2006). Mature individuals can be collected from the wild and induced to spawn during the peak reproductive season, which generally occurs during a change in season when increasing water temperatures are accompanied by a boost in primary production. It is also possible to maintain broodstock year round and condition them in tanks for one month prior to spawning (Duy 2010).

Spawning induction. The most common technique to induce spawning is thermal shock, where broodstock are transferred to tanks where the water temperature is 3-5 °C greater than ambient temperature. Heat-shock treatment can be combined with a Spirulina bath, where 15 g/L of Spirulina is added, the tank drained after 1 hour, rinsed with filtered seawater, and re-filled with ambient, filtered, and UV-sterilized seawater (Gamboa et al. 2012). Males normally spawn first, rising up in a cobra-like stance, releasing sperm from a pore on their head (Fig. 2). Males can spawn for extended periods. To avoid polyspermy, after 10-15 min, males should be removed from the spawning tank. Females, on the other hand, are very sensitive and must not be disturbed during spawning; they generally display characteristic rolling and twisting movements before rising up and releasing jets of orange eggs in a series of 4-5 squirts (Fig. 3).

Read the rest of this article in the March 2013 issue of World Aquaculture Magazine here