Use of marine yeasts as an avilable diet for mass cultures of Moina macrocopa

Abstract

A 4-week feeding trial was conducted to test the use of marine yeasts purified from seawater and sediments as a dietary source in cultivating a cladoceran, Moina macrocopa, a potential alternative live food for fish larvae. Optimal growth conditions of two yeast strains were obtained for NaCl concentration, pH and temperature. Moina macrocopa was cultivated using different diets: marine yeasts (Debaryomyces hansenii Yeast-14 and Candida austromarina Yeast-16) and a commercial diet (Erythrobacter sp. S pi-I). The essential amino acids of both the yeast strains were nearly as great as those in M. microcopa. Further, the yeast-fed M. macrocopa had essential amino acid profiles similar to the documented values for rotifers and Artemia enriched in microalgae and commercial diets. Erythrobacter sp. S pi-I lacked n-3 polyunsaturated fatty acids, 20:5n-3 and 22:6n-3, which were also low but detected in both yeasts. An increase in the 20:5n-3 [eicosapentaenoic acid (EPA)] and 22:6n-3 [docosahexaenoic acid (DHA)] levels, compared with the levels in yeast strains themselves, was more pronounced in the 22:6n-3 level of Moina fed the C. austromarina, resulting in a high DHA:EPA ratio. When the Moina diets were switched, their delta C-13 values shifted gradually towards the values of the switched diets. Diet switch from Erythrobacter sp. S pi-I to C. austromarina Yeast-16 resulted in a more rapid turnover of Moina tissue carbon than that in the inverse case. When fed a mixed diet, the delta C-13 values of Moina tissue approached the value of marine yeasts immediately. These temporal changes in the delta C-13 values of Moina tissue indicate the preferential ingestion of marine yeasts and a selective assimilation of the carbon originated from marine yeasts. These findings suggest that marine yeasts, particularly C. austromarina Yeast-16, are highly available to mass cultures of M. macrocopa, providing better nutritional and dietary values than the commercial diet (Erythrobacter sp. S pi-I).