Comparison of the fatty acid composition of the freshwater fish larvae Tilapia zillii, the rotifer Brachionus calyciflorus, and the microalgae Scenedesmus abundans, Monoraphidium minitum and Chlorella vulgaris in the algae-rotifer-fish larvae food chains

The proximate and the fatty acid analysis of the warm freshwater fish, Tilapia zillii larvae, the freshwater rotifer Brachionus calyciflorus and the microalgae Scenedesmus abundans, Monoraphidium minitum and Chlorella vulgaris each constituting a different food chain with B. calyciflorus and T. zillii larvae have been carried out. C. vulgaris had significantly higher lipid content than the other two microalgae and this was also reflected in the lipid content of B. calyciflorus fed each of the microalgae separately. Five fatty acids dominated in all the microalgae, namely 18:3n - 3, 18:2n - 6, 18:0, 18:1 and 16:0 though there were significant differences both in quantitative distribution of these acids and the total fatty acid content. The content of 18:3n - 3, 18:2n - 6 and 16:0 and the total fatty acid content of C. vulgaris were considerably higher than the corresponding values in the other two microalgae. But interestingly, these strong differences were not reflected in B. calyciflorus samples fed these microalgae separately though the one fed C. vulgaris had slightly higher total fatty acid content than the other two rotifer samples. One can consider that the freshwater rotifer B. calyciflorus is capable of creating its own characteristic fatty acid content up to a sufficient level even when cultured with a fatty acid deficient algae probably by consuming excessive amounts of this algae compared to other algae of relatively high fatty acid content. The proximate and fatty acid analysis results of the three T. zillii larvae fed the three B. calyciflorus samples obtained by culturing with three different microalgae were very similar. This was an expected result because the three B. calyciflorus samples did not differ much from each other. The low 18:2n - 6 (1.66-3.53 mg g(-1) DM) and 18:3n - 3 (1.14-1.22 mg g(-1) DM) content and the relatively high 22:6n - 3 (10.72-14.38 mg g(-1) DM) content of the T. zillii larvae samples indicated that they were capable of elongating and desaturating both linoleic and linolenic acids of the B. calyciflorus samples. (C) 1999 Elsevier Science B.V. All rights reserved.