Sandfish sea cucumbers (Holothuria scabra) are the most valued species in many tropical coastal regions, particularly Asia. This is based on their use in traditional medicine and as a delicacy. Overexploitation has led to population declines in some areas, prompting conservation efforts to protect this critical species. Therefore, sandfish sea cucumbers are no longer caught in the wild; most are reared on specialized farms. The sandfish in these pictures were collected in lagoons outside farms and returned unharmed to their habitat.
Description of sandfish
Sandfish have a cylindrical body with smooth, leathery skin and can grow up to 30 cm (abt. 1 ft.) long. They have typical transverse wrinkles over the dorsal side of their body. They are primarily detritivores, feeding on organic matter in the sediment, such as decomposing plant material and microorganisms. Their feeding behavior contributes to the ecosystem’s health by promoting nutrient recycling.
Distribution of wild sandfish
The sandfish (Holothuria scabra) is a species of sea cucumber found in tropical and subtropical regions of the Indo-Pacific, particularly in the waters of the Red Sea, the coasts of East Africa, Southeast Asia, Australia, and the Pacific Islands.
This species typically inhabits sandy and muddy substrates in shallow coastal areas, often in depths ranging from 1 to 20 meters, although they may be found deeper in some locations. Sandfish are well adapted to bury themselves in the sediment or under rocks, which helps them avoid predators and environmental stressors. The distribution of sandfish is influenced by water temperature, salinity, and substrate type. They are often found in areas with moderate wave action and good water quality.
Internal anatomy of sea cucumbers
The internal anatomy of sea cucumbers is adapted to their burrowing and detritivorous lifestyle. They have a simple digestive system, with a mouth surrounded by tentacles for feeding. The stomach and intestines process organic matter from the sediment.
Sandfish have a unique respiratory system known as the “respiratory trees,” which are specialized organs that extract oxygen from water, extending from the anus into the body cavity. They are therefore breathing through the anus!
The muscles around the anus are surrounded by anal teeth, which should avoid that larger parasites will enter into their body. This does not always help, as many sea cucumbers host pairs of eel-like pearlfish (Carapidae) inside their body. One of these pearlfish species, the worm pearlfish (Encheliophis vermicularis), even specializes in eating the gonads of their hosts.
Their circulatory system is open, lacking a heart, and they rely on the body’s fluid movement for circulation. The body is supported by a hydrostatic skeleton and small calcareous plates embedded in the skin.
How to find and collect sandfish?
Sandfish should not be collected in the wild for food, as they are already overexploited. Instead, they should be collected for research, education, or conservation purposes and returned unharmed to their habitat.
Collecting sandfish is best done during low tide when they are closer to the surface or at night when they tend to come closer to the sand surface for feeding. Early morning or late evening may also offer optimal conditions.
If not found on the surface, it can help to gently sift through the sand with small rakes, as they are often buried there. Small depressions or signs of movement in the sand are a good indication to find them. They can be held gently when caught, avoiding damage to their soft, leathery skin.
Uses of sandfish sea cucumbers
Fresh sea cucumbers for home consumption
Small numbers of live sea cucumbers are either directly used for the collector’s family sustenance or sold in wet markets for domestic consumption. After cleaning, these sea cucumbers will be either barbequed or cooked in stews or soups.
Dried sea cucumbers for export
However, most sandfish sea cucumbers are exported to Asian countries. Processing methods to achieve the dried form (bêche-de-mer) vary depending on the species, the final product, and the market to which the product will be sold. The texture of nearly all sea cucumbers exported to China is expected to be hard and not rubbery.
According to (Purcell et al., 2023), the following preparation and drying procedure is necessary to achieve such hard tack result:
- ‘Cook sea cucumbers in hot (not boiling) water for 5 minutes until they swell.
- Remove the organs by gently squeezing the body or by making a tiny cut in the mouth on the ventral surface, if this is necessary.
- Cook a second time in very hot or boiling water for 15–30 min until rubbery and firm.
- Bury in a sandpit or box with weight on top for 12–18 hours.
- Upon retrieval, rub the outer part of the body to remove chalky deposits.
- Boil a third time for 5–10 min in clean water.
- Drain and dry in hot air.
- Leave to dry in the sun (generally 4–10 days, depending on moisture content)’
The end customers in Asia will reconstitute the dried sea cucumbers and prepare various meals by braising or pan-frying with sauces. Another popular recipe is beef and sea cucumber Jiaozi (Chinese dumplings)
Nutritional value of sandfish sea cucumbers
Sandfish are considered a nutritious food source, particularly in many Asian countries where they are valued for their high protein content and medicinal properties. Their nutritional values are as follows:
- Protein: Sandfish are rich in protein, typically containing around 50-60% protein by dry weight.
- Low Fat: They are low in fat, making them suitable for low-fat diets.
- Vitamins and Minerals: Holothuria scabra are also a good source of essential vitamins and minerals, including calcium, magnesium, and potassium.
- Collagen: Sandfish’s soft tissue is rich in collagen, a protein beneficial for skin, joints, and connective tissues.
- Amino Acids: Their protein comprises essential amino acids crucial for the body’s growth and maintenance.
Due to their low fat and high protein, sandfish are a healthy food choice for those seeking a lean protein source. Additionally, they are often used in traditional medicines in some Asian cultures and are believed to have health benefits beyond their nutritional content.
Lessons learned about wild sandfish sea cucumbers in Zanzibar:
- Sandfish are the most sought-after sea cucumber species worldwide.
- Zanzibar was once rich in this species, but its wild stocks were over-exploited.
- Nowadays, most sandfish sea cucumbers are raised under controlled conditions on farms.
- Wild sandfish sea cucumbers are still regularly found in the lagoons and are primarily caught by male skin divers.
- Some of these holothurns collected in the wild are eaten by the fisherman’s family, but the large majority will be dried and exported to Asian countries.
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