Synthesis, transfer and utilisation of lipids and fatty acids in experimental marine food chains
An analytical procedure has been developed whereby the lipid class composition of marine animals can be accurately and rapidly determined using the Iatroscan TLC-FID analyser. When applied to the study of developing cod eggs, this technique revealed that phosphatidylcholine (PC) was the only lipid class to decline in absolute terms during the period of embryogenesis. A similar trend was apparent during embryogenesis in herring eggs. In contrast, PC and triacylglycerol (TAG) were catabolised to a similar extent during the longer embryogenic period of salmon eggs. Approximately 33% of the fatty acid 22:6(n-3) released from PC in developing cod eggs was preferentially incorporated into neutral lipid. PC catabolism continued during the early development of herring larvae reared in large enclosures, but a greater amount of TAG was catabolised during this period. Following the initiation of feeding, the dietary intake of herring larvae was directed towards growth but larvae soon began to accumulate reserves of TAG. The magnitude of the TAG reserves of herring larvae during the 6 weeks after the initiation of feeding correlated positively with larval nutritional condition. Consequently, there would appear to be considerable potential for a larval condition index based on the quantification of TAG reserves. The TAG content of herring larvae during the period of metamorphosis was minimal but TAG reserves rapidly accumulated in metamorphosed juveniles. Polyunsaturated fatty acids (PUFA) of the (n-3) series represented a high proportion of the fatty acids synthesised by enclosure populations of phytoplankton during the spring bloom period. Changes in the (n-3) PUFA content of phytoplankton could be explained in terms of cell senescence or species succession. Lipid represented a generally consistent proportion (mean S.D. = 21.9% 5.6) of the photosynthetic products of phytoplankton, despite variation in species composition, cell growth stage, nutrient concentration and incubation depth.