Nannochloropsis limnetica: A freshwater microalga for marine aquaculture

Abstract

Despite the availability of inert commercial feeds, microalgae are still the preferred feed for mass production and enrichment of the rotifer Brachionus plicatilis. Although good growth results can be obtained with different freshwater Chlorella species, marine species of the genus Nannochloropsis are most commonly used due to their high growth rate and content in polyunsaturated fatty acids, mainly EPA. In this work we explored the response of the freshwater species Nannochloropsis limnetica to different temperatures in semi-continuous cultures and compared its nutritional value for the rotifer B. plicatilis to that of the marine species Nannochloropsis gaditana both at laboratory scale and in hatchery facilities. N. limnetica could be cultured in the range 15–27 °C with highest dry-weight productivities at 22 °C. When compared with N. gaditana in semicontinuous cultures at laboratory scale, with a daily 40% harvesting rate, productivity of both species was similar, reaching a daily production of 0.64 g L−1 day−1. Both species have an almost identical fatty acid profile. In laboratory-scale cultures with high algal rations, growth and egg-ratios of the rotifer B. plicatilis cultured with N. limnetica were more than twice than with the same doses of N. gaditana, while maintaining the same fatty acid profile in the filter-feeder, confirming the potential of this freshwater species for marine aquaculture. In hatchery-scale experiments in which B. plicatilis was fed with baker's yeast supplemented either with on-site produced fresh microalgal cultures or with concentrated algae, similar growth results were obtained for both microalgal species in 5-day batch cultures, although higher dry weights and slightly better egg ratios were observed with the freshwater species. Results indicate the potential of this freshwater species as a substitute of freshwater Chlorella in live-feed production protocols, due to its better fatty acid profile. Statement relevance: The freshwater microalga Nannochloropsis limnetica promotes higher growth in the rotifer Brachionus plicatilis than the marine species N. gaditana. Results indicate the potential of this species as a substitute of freshwater Chlorella due to its better fatty acid profile. Moreover, no potentially pathogenic marine bacteria would be present in cultures of the freshwater species in comparison to its marine counterparts.