Developing hatchery culture of the tropical sea cucumber, Holothuria scabra, using micro-algae concentrates

Abstract

Major bottlenecks to further development and expansion of hatchery-based production of tropical sea cucumbers include our lack of knowledge of their nutritional requirements and appropriate foods for larval stages. Live micro-algae have been used as the main source of food for hatchery culture. However, mass culture of adequate volumes of high quality cultured micro-algae is both labour and resource demanding and is often inappropriate for small-scale hatcheries in developing countries that generally lack the required resources and technical capacity. Alternative potential food sources for larvae include highly-concentrated marine micro-algae that is now available commercially. This study assessed the potential of commercially available micro-algae concentrates as a replacement for live cultured microalgae during hatchery culture of sandfish, Holothuria scabra. It examined ingestion and digestion of micro-algae concentrates by larval sandfish (Chapter 3), the nutritional value of micro-algae concentrates for larval sandfish during hatchery culture (Chapter 4), the relationships between hyaline spheres formation, larval food composition and subsequent settlement success (Chapter 5), and the ingestion, digestion and nutritional value of live microalgae and micro-algae concentrates for newly settled sandfish juveniles (Chapter 6). Ingestion and digestion of two live (TISO and Chaetoceros muelleri) and six concentrated micro-algae products (Instant Algae®, Reed Mariculture Inc., Campbell, CA, USA, 95008) by sandfish auricularia larvae of different ages were assessed using epifluorescence microscopy. The commercial micro-algae products were purchased from an Australian distributor. They were: (1) mono-cultured Isochrysis sp. (Haptophyceae) (Isochrysis 1800®); (2) mono-cultured Pavlova sp. (Haptophyceae) (Pavlova 1800®); (3) mono-cultured Tetraselmis sp. (Chlorophycophyceae) (Tetraselmis 3600®); (4) mono–cultured Thalassiosira weissflogii (Bacillariophyceae) (TW 1200®); (5) mono-cultured Thalassiosira pseudonana (Bacillariophyceae) (3H 1800®); and (6) a mix of four concentrated single micro-algae species: Isochrysis sp., Pavlova sp. Thalassiosira pseudonana and Tetraselmis sp. (Shellfish Diet 1800®). 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 micro-algae tested were ingested and digested by larvae with digestion occurring more rapidly in older larvae. C. muelleri was rapidly digested by 6-day and 10-day old larvae but 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 micro-algae tested in terms of ingestion and digestibility. All commercially available micro-algae concentrates tested were readily ingested and digested by H. scabra larvae with the exception of Thalassiosira pseudonana (3H 1800®) which was not…