The gross and amino acid compositions of batch and semi-continuous cultures of Isochrysis sp. (clone T.ISO), Pavlova lutheri and Nannochloropsis oculata

Three species of microalgae commonly used in mariculture - Isochrysis sp. (clone T.ISO), Pavlova lutheri and Nannochloropsis oculata - were grown in batch and semicontinuous modes to compare their biochemical composition and production rates. In batch mode, logarithmic-phase cultures of all species had high levels of protein (25.2 to 41.1%) and low levels of carbohydrate (7.1 to 10.3%) and lipid (8.8 to 14.9%). At stationary phase, cultures of Isochrysis sp. (clone T.ISO) and N. oculata contained significantly less protein (21.8% and 20.3%, respectively), all species contained more carbohydrate (14.8 to 30.6%), and P. lutheri contained more lipid (16.6%). In semi-continuous mode, cultures maintained at late logarithmic-phase contained more carbohydrate, Isochrysis sp. (clone T.ISO) contained less protein, and P. lutheri more lipid than logarithmic-phase batch cultures of the same species. Neither growth phase nor harvest regime affected the amino acid composition of the microalgae significantly. However, the concentration of proline in N. oculata was higher in batch cultures in logarithmic phase (9.4%), than in either semi-continuous cultures in logarithmic phase (5.8 to 7.9%) or batch cultures in stationary phase (5.6 to 5.9%). The production rates from batch and semi-continuous logarithmic-phase cultures were not significantly different for any of the species, and there were only minor differences in the production rates of the species (range 12.4 to 17.1 mg algae dry weight/l/d). The different culture and harvest regimes produced significant differences in the proportions of protein and carbohydrate in the microalgae. Which regime is chosen for culturing these microalgae as food will depend on the nutritional requirements of the animal species being fed.