Enhanced larval performance of Holothuria arguinensis using mixed microalgae diets: Comparative effects of Isochrysis sp. and Rhodomonas sp. on growth, survival, and development

Abstract

Sea cucumber aquaculture represents a sustainable alternative to wild fisheries to supply the exponential demand for this product. Yet larval rearing remains a critical bottleneck in the production of European sea cucumbers. This study investigated the effects of different microalgae feeding regimes on larval development, growth, and settlement competency of Holothuria arguinensis, a promising candidate species for European aquaculture. Larvae were daily fed either a single-species diet of Isochrysis sp. (10,000 cells mL−1) or a mixed diet combining Rhodomonas sp. and Isochrysis sp. (5000 cells mL−1 each), over a four-week period. Biochemical analyses revealed that Rhodomonas sp. contributed elevated protein content (44.51%) and n-3 polyunsaturated fatty acids (54.25%), particularly eicosapentaenoic acid (EPA, 5.68%), while Isochrysis sp. provided high lipid content (30.18%). Larvae fed the mixed diet exhibited significantly enhanced performance across multiple parameters: wider body dimensions at the late auricularia stage (744.31 ± 130.57 μm), higher survival rates (62.11% vs. 40.44% at 14 days post-fertilization), accelerated formation of hyaline spheres, and most notably, exclusive progression to pentactula and juvenile stages within the experimental timeframe. This represented a 53.6% improvement in survival rates at 14 dpf compared to the monospecific diet. By day 28, all larvae in the mixed treatment had successfully reached the juvenile stage, whereas those fed Isochrysis sp. alone remained at earlier developmental stages. These findings demonstrate that dietary diversity and complementary biochemical composition are critical determinants of larval performance in H. arguinensis, providing valuable insights for optimizing feeding protocols in commercial hatchery operations and advancing sustainable sea cucumber aquaculture expansion in Europe.