Diet-tissue Stable Isotopic Fractionation of Tropical Sea Cucumber, Holothuria scabra

Abstract

Many species of tropical sea cucumbers in many countries in the Pacific and Indian Oceans are being over-exploited for processing into bêche-de-mer (dried form) 5,8,18 . As the demand for sea cucumbers increases and fishery stocks dwindle in many areas of these countries, there is a growing demand to produce sea cucumbers by aquaculture and stock enhancement using juveniles produced in the hatchery. There is also growing interest in co-culturing sea cucumbers alongside other organisms to utilize organic debris and thus mitigate eutrophication within and around the aquaculture facilities 4,22,33,37,46 . To this end, an increasing number of studies have recently been performed to develop techniques for hatchery, aquaculture and stock enhancement of sea cucumbers, especially sandfish, Holothuria scabra, the most valued species of tropical sea cucumbers 3,4,28,37 . The hatchery production of H. scabra seeds has got underway in countries, such as Vietnam, India, New Caledonia and the Philippines 1,11,36 , but the high mortality and slow growth rate of cultured juveniles have been problematic. Despite the various food items used in broodstock maintenance and juvenile production and grow-out of H. scabra, including Spirulina spp, Schizochytrium spp, Navicula spp, homogenized Sargassum spp, ground shrimp feed, shrimp head meal, soya bean powder, rice bran, chicken manure and seagrass powder 1,3,11,36 , juveniles often grow much faster in sea pens or earthen ponds where no artificial feeding is conducted. Information about H. scabra diets is indispensable in improving hatchery, aquaculture and reseeding techniques, as well as monitoring environmental conditions for wild stocks.H. scabra are benthic detritus feeders, which ingest muddy sandy sediment and assimilate the organic matter AbstractTo provide a basis for a stable carbon and nitrogen isotope ratio (δ 13 C / δ 15 N) analysis to determine the assimilated organic matter in sea cucumber, Holothuria scabra, diet-tissue fractionations were experimentally determined by mono-feeding rearing with diatom. While δ 15

Assimilation Dynamics of Different Diet Sources by the Sea Cucumber Holothuria scabra, with Evidence from Stable Isotope Signature

“…Therefore it is likely that detritus, as a result of processed diet sources, has a significant contribution to the sediment composition. These results confirm the previous study by [30] that indicates similar low assimilation patterns by comparing the isotopic 's fecal pellet and its potential ).…”

“…It is well known that enrichment of carbon and nitrogen stable isotopes for consumers relative to their diet is 1 and 3.4‰ respectively [24, 32,33]. Even the isotopic value of H. scabra obtained from secondary data [30] has lower δ 15 N values compared to primary data of this study. Both [30] and this study use an acidification process for removing carbonate content from the samples that may affect the reduction of the nitrogen isotopic value [34].…”

“…Both [30] and this study use an acidification process for removing carbonate content from the samples that may affect the reduction of the nitrogen isotopic value [34]. Watanabe et al [30] estimated that the mean δ 15 N fractionation for the intestine (1.5‰) to be about half of the common range; meanwhile the mean δ 13 C fractionation for the intestine (2.2‰) was about double the common range.…”

“…In order to obtain a more comprehensive snapshot, also secondary data of stable isotope signature were included in the biplot. Stable isotope signature of H. scabra body wall and intestine (H.s.b.w and H.s.i.x) refer to [30]. Additional stable isotope signature of the prospected diets (Enhalus acoroides/ Ea2, Thalassia hemprichi/ Th and suspended particulate matter/ SPM) refer to [31].…”

Growth Pattern of the Tropical Sea Cucumber, Holothuria scabra, under Captivity

“…Accordingly, there has been growing interest in developing hatchery, aquaculture and stock enhancement techniques; particularly for sandfish, Holothuria scabra, one of the most valued tropical sea cucumber species (Battaglene et al 1999, Purcell & Kirby 2006. There has also been growing interest in developing polyculture methods using sea cucumbers, which can consume nutrient from aquaculture debris and thus bio-mitigate environmental degradation (Ahlgren 1998, Slater & Carton 2007, Pitt et al 2004, Watanabe et al 2012a, Watanabe et al 2013. However, there is a paucity of basic biological and ecological information of H. scabra to design an effective polyculture system.…”