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

Abstract

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.