The vitamin content of microalgae used in aquaculture

Abstract

The vitamin content in four Australian microalgae, a Nannochloropsis-like sp., Pavlova pinguis, Stichococcus sp. and Tetraselmis sp., were examined. These were grown under a 12:12 h light:dark regimen (100 μmol photon m⁻²s⁻¹) and harvested during late-logarithmic phase. Typically, the content showed a two- to three fold range between the species. When expressed on a dry weight basis, the content of ascorbate ranged from 1.3 to 3.0 mg g⁻¹, β-carotene from 0.37 to 1.05 mg g⁻¹, α-tocopherol from 0.07 to 0.29 mg g⁻¹, thiamine from 29 to 109 μg g⁻¹, riboflavin from 25 to 50 μg g⁻¹, total folates from 17 to 24 μg g⁻¹, pyridoxine from 3.6 to 17 μg g⁻¹, cobalamin from 1.70 to 1.95 μg g⁻¹ and biotin from 1.1 to 1.9 μg g⁻¹. Retinol was detected only in Tetraselmis sp. (2.2 μg g⁻¹); any vitamins D₂ or D₃ were below the detection limit (≤0.45 μg g⁻¹). Nannochloropsis sp. was also grown under a 24:0 h light:dark light cycle and harvested at stationary phase. The content of most vitamins in Nannochloropsis sp. cultures differed significantly, and the degree of variation was similar to that observed between the four species grown under 12:12 h light:dark regimen (100 μmol photon m⁻²s⁻¹) and harvested during late-logarithmic phase. Thiamine content was also examined in six non-Australian strains commonly used in aquaculture, Chaetoceros muelleri, Thalassiosira pseudonana, Nannochloris atomus, Nannochloropsis oculata, Isochrysis sp. (T.ISO) and Pavlova lutheri. Values (average 61 μg g⁻¹; range 40 to 82) were similar to those in the Australian strains (average 61 μg g⁻¹; range 29 to 109) and increased during stationary phase (average 94 μg g⁻¹; 38 to 131). Comparison of the data with the known nutritional requirements for marine fish species and prawns suggests that the microalgae should provide excess or adequate levels of the vitamins for aquaculture food chains. The data may be used to guide the content of vitamins included in micro-diets developed as replacements for live diets.