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

The sea cucumber Holothuria scabra has a high commercial value and a great potential to be cultivated. A thorough feeding strategy is needed to overcome juvenile rearing technique constraints. Stable isotope analysis can be used for determining diet sources of sea cucumbers that play a role as deposit feeders. This study aims to determine suitable diet sources and elucidate the potential of organic matter assimilation of H. scabra by combining three different mixed diets including 10% seagrass Enhalus acoroides bulk, 45% grass Pennisetum purpureum and 45% of cow feces (diet A); 20% seagrass E. acoroides, 40% grass P. purpureum and 40% of cow feces (diet B) and 33% seagrass E. acoroides, 33% grass P. purpureum and 33% cow feces (diet C) and identifying the fecal pellet isotopic properties and compare it to the diet sources and the surrounding sediment. Stable isotope signature of H. scabra and its prospected diet sources, altogether with sediments and fecal pellets were plotted in a conservative bi-plot δ13C and δ15N. The isotopic value of fecal pellets and diet sources indicate a low assimilation rate, the organic matter contained in the sediment is similar to that of the diet sources. Sea cucumber feeds the bulk of the sediment and the detritus of the diet sources and then assimilates the organic matter as soon as the bulk enters the intestine. Due to the low assimilation rates, we suggest for the mariculture of H. scabra that the food should be homogenised and then mixed into the sediment, where the sea cucumber is cultured.

Inferior Assimilation of Algae-based Diets by Sea Cucumber Holothuria scabra under Laboratory Condition Expressed by Stable Isotope Mixing Model

Aim: To investigate the dietary preferences of sea cucumber Holothuria scabra fed with algal food sources like Sargassum, Fucus, Spirulina, Ulva in combination with marine pellet under laboratory condition. Carbon stable isotope technique (δ13C) was used to better understand the assimilation of different dietary food sources. Study Design: A microcosm approach was undertaken where 24 experimental aquaria were set up, each having juvenile H. scabra. These aquaria were segregated into four different dietary treatments with six replicates per treatment. (SGP treatment= Sargassum + marine pellet, FCP treatment= Fucus + marine pellet, SPP treatment= Spirulina + marine pellet, ULP treatment= Ulva + marine pellet). Place and Duration of Study: Marine Experimental Ecology Unit (MAREE), Leibniz Centre for Tropical Marine Research, Bremen, Germany, between January and October 2017. Methodology: We included 24 sea cucumber juveniles for conducting the feeding trial. CN contents, C/N ratio and carbon stable isotopes were measured in food sources as well as in H. scabra body wall. The growth of H. scabra was also monitored. Stable isotope mixing model was used to calculate the exact food preference under laboratory condition. Results: The results of carbon stable isotopes (δ13C) of sea cucumber body wall exhibited depleted values that are significantly different (ANOVA, P˂0.05) from all the dietary treatments (SGP, FCP, SPP, ULP) thereby suggesting inferior assimilation of food ingredients. The poor performance of selected food sources (algae and marine pellet) towards the growth of sea cucumber was clearly reflected in the data (ANOVA, P>0.05). Conclusion: Therefore, it is assumed that some additional food source co-existed within the microcosm and could have contributed to their food uptake, probably sediment microbes that require further clarification.

No Difference in Nutritional Profiles of Wild and Cultured Juvenile Sandfish, Holothuria scabra

The demand for sandfish, Holothuria scabra has rapidly grown in the last decades. In order to better understand the quality of this species as human food, nutritional profiles of farmed and wild juvenile sandfish were investigated in this study by measuring the proximate body compositions of carbohydrates, proteins and lipids, including the amino acid and fatty acid contents. Body wall of juvenile wild sandfish from Medana and Sekotong in Lombok, Indonesia were compared with body wall of juveniles cultivated at Marine Bio Industry LIPI, and fed with mashed sea grass Enhalus acoroides leaves for a three months feeding period. The results show that protein, lipid and carbohydrate contents of juvenile farmed sandfish were similar to juvenile wild sandfish. Amino acid compositions of wild and farmed juvenile sandfish predominantly consist of glycine, glutamic acid and alanine. Polyunsaturated fatty acids (PUFAs) were the major fatty acids in the body wall of wild and farmed H. scabra. Arachidonic acid (C20:4n6) was recorded as the highest component among all PUFAs. The contents of total PUFAs, total omega-3 and total omega-6 in the body wall of farmed H. scabra were slightly higher compared to wild H. scabra. In summary, both wild and farmed juvenile sandfish contain high amounts of valuable nutrients that have the potential to be used as a functional food for human health due to beneficial FA ratios, besides being adelicious and healthy seafood for human consumption.

Length-weight Relationships of Four Commercially Important Fish Species in Indonesia

Length-frequencies and length-weight relationships of the four economically important fish species Encrasicholina heteroloba (Rüppel 1837), E. punctifer Fowler 1938, Katsuwonus pelamis (Linnaeus 1758) and Rastrelliger kanagurta (Cuvier 1816) were analysed to assess the condition of the respective stocks. Length-frequency data were analysed to estimate the theoretical maximum size of fish in a stock (L∞) and the coefficient K, indicating how fast fish reach that size. A power model approach was used with length and weight data to estimate the condition factor a and allometry coefficient b. The two anchovy species (Encrasicholina) showed similar values with = 9.45 cm, K = 1.10 year-1, a = 0.00672 and b = 2.919 for E. heteroloba and L∞ = 10.78 cm, K = 1.00 year-1, a = 0.01031 and b = 2.871 for E. punctifer. For both species, the allometry coefficient was below 3, implying allometric growth. The estimated parameters for the skipjack tuna K. pelamis and the Indian mackerel R. kanagurta were L∞= 72.32 cm, K = 0.38, a = 0.0395 and b = 2.766 and L∞= 27.83 cm, K = 0.92, a = 0.00556 and b = 3.216, respectively. All data were collected in Pasir Kendang, Padang, West-Sumatra in 1993 and 1994.