Ingestion and digestion of live microalgae and microalgae concentrates by sandfish, Holothuria scabra, larvae

Information on the nutritional requirements and preferred diets of sea cucumber (Holothuriidae) larvae is extremely limited and this has hindered development of hatchery culture methods. This study assessed ingestion and digestion of two live (TISO and Chaetoceros muelleri) and six concentrated microalgae (Instant Algae®, Reed Mariculture Inc.) by sandfish (Holothuria scabra) auricularia larvae of different ages using epifluorescence microscopy. This is the first study to report the use of epifluorescence microscopy with larval echinoderms and experiments were conducted using 2, 6 and 10 day old auricularia larvae. Seven of the eight microalgae tested were ingested and digested by the larvae with digestion occurring more rapidly in older larvae. C. muelleri was rapidly digested by 6-day and 10-day old larvae but our results indicate that C. muelleri is unsuitable as a food for 2-day old sandfish larvae. TISO was well ingested by sandfish larvae in both live and concentrated forms and live TISO was the most suitable of the microalgae tested in terms of ingestion and digestibility. All commercially available microalgae concentrates tested were readily ingested and digested by H. scabra larvae with the exception of Thalassiosira pseudonana (3H 1800®) which was not ingested by larvae of any of the three ages tested. Our results show potential for using microalgae concentrates as alternatives to live microalgae in hatchery culture of sandfish. However, further research should be conducted to assess the relative nutritional values of digestible microalgae as a basis for optimising a diet for hatchery culture of sandfish, and to provide further information on the nutritional requirements of sandfish larvae.