Usefulness of the euglenophyte Eutreptiella eupharyngea as a new diet alga for clam culture

Abstract Microalgae are an essential primary feed source in aquaculture. However, there is a deficiency of microalgae that can provide a stable supply of nutrient-rich feed at low water temperatures during the winter and spring. The aim of this study was to develop a new diet microalga that can grow well outdoors at low water temperatures and possesses the essential nutritive constituents. In laboratory experiments, the euglenophyte Eutreptiella eupharyngea grew well at water temperatures of 10–25 °C, but could not grow at 30 °C. In outdoor experiments, E. eupharyngea also grew well in mid-winter, and produced maximum cell densities of 3.2 × 10 5 cells mL −1 and 2.5 × 10 5 cells mL −1 at salinities of 25 and 30, respectively. During these experiments, water temperatures ranged from 4.0 to 20.3 °C, with a mean of 10.1 °C. The dietary effect of E. eupharyngea per dry weight on juvenile Ruditapes philippinarum of >1.5 mm shell length exceeded that of the diatom Chaetoceros neogracile . These findings are attributable to the high nutritional value of E. eupharyngea as typified by its high protein and sugar content and high content ratio of n-3 fatty acids such as eicosapentaenoic and docosahexaenoic acid and n-6 fatty acids such as arachidonic acid. This high nutritional value, combined with the species' high growth potential at low temperatures, means that E. eupharyngea may offer significant advantages as a new diet alga for the seed production of mollusks in late fall and spring.