Sandfish (Holothuria scabra) have the same general anatomy as other sea cucumbers. The gonads (ovaries or testes) lie in one tuft and open dorsally at the anterior end of the body through a single gonopore (i.e. genital orifice). The digestive system is composed of a mouth, oesophagus, stomach, intestine, cloaca and anus. Respiratory trees, which sandfish use to obtain oxygen, lie in the posterior of the body and open to the cloaca. The body wall that is processed into bêche-de-mer accounts for about 56% of total weight.
Sandfish move with the help of tube feet densely distributed on the ventral face, and through muscular action of the body wall. Sandfish feed on detritus, i.e. organic matter in the mud or sand. They appear to feed continuously using the peltate tentacles surrounding the mouth to place sediment into the mouth. Sandfish are usually observed partially buried in sediment. The daily burrowing cycle varies according to environmental conditions.
The growth rate of sandfish depends on environmental conditions and the time of year. At medium size, sandfish grow on average 0.5cm per month, corresponding to 14g per month. Under good conditions they grow to a size of 300g in one year. We still do not know how long sandfish live, but it may be around 10 years.
Sea cucumbers have tiny calcareous plates called spicules in their skin. Microscopic examination of spicules is used to distinguish species. Sandfish have many spicules in the shape of tables and knobbed buttons.Sandfish can be sexually mature at a size as small as 200g. There is no apparent relationship between fecundity (egg production) and body size.
Like other sea cucumbers, sandfish can regenerate some of their organs. After spending long periods out of water, or being affected by the use of chemicals, being handled during collection and transport, or when stressed by predators, sandfish may eviscerate their internal organs. Regeneration of internal organs occurs within 2 months. Sandfish and other tropical sea cucumbers can produce numerous toxins from their skin and viscera. These toxins inflict distress, loss of equilibrium and death in fish, but do not affect humans.
Sandfish are found in many countries in the Indo-Pacific, from east Africa to the eastern Pacific. They are usually found between the latitudes of 30°N and 30°S.
The preferred habitats of sandfish are shallow tropical waters, usually less than 20m deep, such as sheltered areas with high levels of nutrients, including muddy substrata and seagrass beds. They can tolerate reduced salinity (20 ppt) for short periods and so are sometimes found in brackish water.