Effects of monospecific and mixed-algae diets on survival, development andfatty acid composition of penaeid prawn (Penaeus spp.) larvae

Four species of microalgae (Chaetoceros muelleri, Tetraselmis suecica, Tahi tian Isochrysis sp. (T-iso) and Dunaliella tertiolecta) with distinctly dif ferent fatty acid profiles were grown in continuous culture and fed to praw n larvae (Penaeus japonicus, P. semisulcatus and P. monodon) as monospecifi c diets. The best two diets (C. muelleri and T. suecica) were also fed as a mixed diet. Experiments were run until the larvae fed the control diet of C. muelleri metamorphosed to Mysis 1. The survival and development (i.e. pe rformance) of the larvae were affected by algal diet, and the diets were ra nked in the order of decreasing nutritional value: C. mueller greater than or equal to T. suecica > T-iso > D. tertiolecta. Larvae fed a mixed diet of C. muelleri and T. suecica (2:3 by dry weight) performed as well or better than those fed C. muelleri, and the performance of both these groups of la rvae was better than those fed T. suecica. The lipid and carbohydrate compo sitions of the algae had little or no effect on the lipid and carbohydrate compositions of the larvae or their performance. However, the larvae that p erformed best (i.e. those fed C. muelleri) had significantly more lipid and carbohydrate than those that performed worst (i.e. those fed D. tertiolect a). Larvae fed C. muelleri or the mixed-algae diet had higher pro portions of the essential fatty acids eicosapentaenoic acid [EPA, 20:5(n-3)] and ara chidonic acid [ARA, 20:4(n-6)] than the larvae fed on other diets. Furtherm ore, the larvae fed T. suecica, which showed intermediate performance betwe en larvae fed C. muelleri and T-iso or D. tertiolecta, also had higher prop ortions of EPA and ARA. Both C. muelleri and T. suecica contained EPA and A RA, but T-iso and D. tertiolecta did not, except for trace amounts of EPA i n T-iso. The fatty acid ARA appears to be much more important in the diet o f larval prawns than has so far been considered. The level of the essential fatty acid docosahexaenoic acid [DHA, 22:6(n-3)] in the algal diet and the larvae was not related to the performance of the larvae; only C. muelleri and T-iso contained DHA. However, the nauplii contained large proportions o f DHA, suggesting that these were sufficient to meet the larval requirement s for DHA during their development to Mysis 1. Mixed-algae diets could impr ove the performance of larvae by providing a more comprehensive range of fa tty acids.