Difference in Nutritive Value of a Microalga Nannochloropsis oculata at Various Growth Phases

Abstract

A microalga Nannochloropsis oculata is commonly used as a food for mass culture of the rotifer, Blachionus plicatilis. The nutritive value of rotifers for fish larvae is evaluated by the ω3 highly unsaturated fatty acids (ω3 HUFA), especially eicosapentaenoic acid (EPA) through the alga. To produce effectively the algal cells with high nutritive value, the changes of chemical components, crude protein, crude lipid, crude ash, fatty acids and amino acids in two strains of N. oculata during the growth were examined. The cells were cultured at 25°C and 3–4 klx light and in low salinity condition 30‰. The initial cells (1X105 cells/m/ and 4X105 cells/ ml) were inoculated into the fertilized media in glass jars (10l) containing 100 mg/l ammonium sulfate, 20 mg/l calcium superphosphate, and 4 mg/l Clewat-32. The contents of EPA and crude protein in the cells at the stationary phase reduced respectively to 60% and 66% (NRIA strain) or 35% and 40% (Chinese strain) in comparison with the exponential growth phase, which continued for 5–7 days after inoculation. The most effective production of N. oculata containing the highest EPA was estimated to be attained at about 7 days after inoculation under suitable conditions (25°C, S=30%0‰, 3–4 klx). © 1990, The Japanese Society of Fisheries Science. All rights reserved.