Wednesday , 23 September 2020

Sandfish: expensive, endangered, and ecologically essential

A box of dried sea cucumbers sold at a store in Hong Kong for HK$4,280. Photo by JP Altamirano

 

Sandfish, or Holothuria scabra, is one of the most threatened tropical sea cucumbers because of its high price, reaching up to $1,600 per kilogram (approximately P80,800) when processed and dried into trepang or beche-de-mer which are used in exotic Asian cuisine and medicinal products.

Because of the high demand for these expensive invertebrates, their natural population have drastically decreased in the recent decades. These creatures live in shallow sand flats and seagrass beds where gleaners can easily pick them up from among their close relatives, the starfishes and sea urchins.

Thankfully, sandfish is among the easiest to propagate of the tropical sea cucumbers because of established hatchery production techniques; thus, providing hope to alleviate the threat to their numbers in the wild.

Production of sandfish, from the hatchery to the farm, is being optimized at one of the leading institutions in sandfish research – the Southeast Asian Fisheries Development Center Aquaculture Department (SEAFDEC/AQD) based in Tigbauan, Iloilo.

Through science, the institution aims to replenish their numbers in the wild and promote a healthier environment where the sandfish are grown.

Just off the shores of Molocaboc Island in Sagay, Negros Occidental, overharvesting reduced stocks to a mere three sandfish per hectare prior to 2015. That number has grown by fortyfold since SEAFDEC/AQD released hatchery-grown sandfish in the area in 2015.

The release of sandfish, which began in 2015, was part of SEAFDEC/AQD’s successful community-based sea ranching project which also released abalone beginning 2011 after years of social preparation.

Aside from their economic value, sandfish also play an important role in keeping the marine environment healthy.

Sandfish regularly bury into the sediments every day from early morning until the late afternoon, as documented in a study by SEAFDEC/AQD sandfish expert Dr. Jon Altamirano and his team published in Fisheries Research in 2017. This “plowing” behavior helps mix available nutrients and oxygenate the sediments.

Sandfish also feed by grazing on the surface of the sediments, ingesting everything that can fit through its mouth – from small animals and plants, decaying matter, and even bacteria and sand particles. In effect, they re-work and transform all these materials in their gut and discharged as “useful” feces.

Because of these environment-friendly behaviors, sandfish and other sea cucumbers are often referred to as the earthworms of the sea.

In another research published in 2012 by SEAFDEC/AQD’s visiting scientist Dr. Satoshi Watanabe and his team, sandfish juveniles in tanks grew much better when fed with detritus (organic matter from decomposing plants and animals) and shrimp feces collected from tiger shrimp culture ponds.  Studies like this show that sandfish may also potentially help minimize wastes accumulation in some aquaculture systems. / RH LEDESMA

A buried sandfish emerging to feed at the sea ranch site in Molocaboc Island, Sagay, Negros Occidental. Photo by JP Altamirano

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