Influence of cell density of Escherichia coli and the dinoflagellate Crypthecodinium cohnii on life history traits of the nematode Panagrolaimus sp. strain NFS 24-5, a potential larval food for marine aquaculture

Abstract

The nematodePanagrolaimussp. NFS 24-5 has potential for use as living food for larval shrimps and fish in marine aquaculture. The nematodes are usually produced on bacterial or yeast cells. Nematodes cannot synthesise the long chain fatty acid docosahexaenoic acid (DHA) which is essential for feeding marine aquaculture organisms. The eukaryotic, heterotrophic dinoflagellateCrypthecodinium cohniiconsists of approximately 20% DHA. To culture the nematodes and simultaneously enrich them with DHA, single adult male and female individuals were cultured in hanging drops with variable cell density ofC. cohnii. Life history traits, such as net reproductive rate (), population doubling time (PDT) and intrinsic rate of natural increase (), were assessed and compared with data obtained from cultures onEscherichia coli. A maximum was recorded at a cell density of 4 × 106C. cohniicells ml−1, corresponding to 2478.82 μg dry mass ml−1. The same was achieved with 7× lower biomass ofE. coliat a cell density of 3 × 109cells ml−1, corresponding to 335.63 μg dry mass ml−1. The results exclude the use of the dinoflagellate culture from application in mass production of the nematode for aquaculture food and limit the use to post-harvest enrichment of the nematodes with essential fatty acids. At a density of 3 × 109E. colicells ml−1the PDT was lowest and the was highest, indicating that this cell density might be closest to optimum conditions for nematode reproduction. Exceeding this cell density yielded fewer offspring within a longer time period. Implications for mass production in monoxenic liquid cultures are discussed.