Development of hyaline spheres in late auriculariae of sandfish, Holothuria scabra: Is it a reliable indicator of subsequent performance?

This study assessed the influence of diet composition on hyaline sphere (HS) development in auricularia larvae of the sandfish, Holothuria scabra , and the subsequent relationships between the presence and size of hyaline spheres and competency through settlement and early juvenile performance. Two-day old larvae were fed one of three commercially available micro-algae diets that varied in their nutrient compositions: (1) Isochrysis sp. (Haptophyceae); (2) Pavlova sp. (Haptophyceae); and (3) Thalassiosira weissflogii (Bacillariophyceae) or a ternary combination of the three. There were positive significant correlations between HS development in late auriculariae on days 10, 11, 12 and 13 post-fertilisation, and the proportion of competent doliolariae on day 15, post-settlement size (day 21) and post-settlement survival (day 25). The dietary components that most strongly influenced these relationships were carbohydrates and the n-3 polyunsaturated fatty acids arachidonic acid (ARA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Our result confirm the strong relationship between HS formation in late auriculariae of sandfish and subsequent larval competency through settlement. As such, the presence and size of HS is a reliable indicator of subsequent performance for sandfish. Given that HS development was influenced by the nutrients available to sandfish auriculariae, there is clear opportunity for development of more appropriate diets for hatchery culture of this species that will improve HS formation and larval performance supporting improved hatchery production. Statement of relevance Our results have confirmed that for sandfish larvae, the presence and size of HS at the end of the auricularia stage, is indeed a reliable indicator of subsequent performance. Our results have also confirmed that HS formation and size is significantly influenced by the nutrient composition of the auricularia diet, and that there are significant positive correlations between HS formation and dietary levels of carbohydrate, EPA:DHA and EPA:ARA ratios. This information provides a strong basis for development of more appropriate diets for sandfish larvae that will improve HS formation and larval performance during hatchery culture and in turn improve hatchery production of this species. [ABSTRACT FROM AUTHOR]