Nutritional value of selected species of microalgae for larvae and early post-set juveniles of the Pacific geoduck clam, Panopea generosa

Abstract The nutritional value of eight species of microalgae for larvae and early post-set juveniles of the Pacific geoduck clam, Panopea generosa , was evaluated. The microalgae tested included two prymnesiophytes, Pavlova lutheri (PL) and Tisochrysis lutea (TL); two chlorophytes, Dunaliella tertiolecta (DT) and Tetraselmis suecica (TS); and four diatoms, Chaetoceros calcitrans (CC), Chaetoceros muelleri (CM), Phaeodactylum tricornutum (PT), and Thalassiosira pseudonana (TP). These microalgae were first tested as mono-species diets on both larvae and early post-set juveniles. The resultant best-performing mono-species diet was then tested as the major component in mixed- (bi-, tri-, and tetra-) species diets. Further experiments examined the possibility that the best-performing mixed-species diet could be improved by adding another algal species. The optimal diet, with the fewest number of algal species to support the best growth, was the bi-species diets of CC + TL for larvae and CM + TL for early post-set juveniles. The fatty-acid profiles of juveniles were influenced by the diets. Although no clear pattern between the level of any particular nutrient and growth and development of juveniles was evident, it appears that a balanced mixture of various dietary nutrients is important. Attention was given to the ratios between n − 3 and n − 6 fatty acids and between eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The best-performing diets, including the optimal one, had a n − 3/n − 6 ratio of 2.17–3.03 and an EPA/DHA ratio of 1.28–3.25 for larvae and 1.84–2.58 and 1.84–2.63, respectively, for early post-set juveniles. Results of this study can be applied to improve the commercial hatchery production of geoduck seed. Statement of relevance Nutritional value of microalgae for young geoduck clams.