Apparent in Vivo Δ-6 Desaturase Activity, Efficiency, and Affinity Are Affected by Total Dietary C18 PUFA in the Freshwater Fish Murray Cod

Dietary fatty acids are known to modulate fatty acid metabolism in fish. However, the innate capability of fish to bioconvert short chain fatty acids to health promoting long chain fatty acids (LCPUFA) is insufficient to compensate for a reduced dietary intake. While many studies have focused on the dietary regulation of the fatty acid bioconversion pathways, there is little known regarding the effects of the dietary levels of C-18 polyunsaturated fatty acids (PUFA) on fatty acid metabolism. Here, we show a greater degree of apparent enzyme activity (Delta-6 desaturase) in fish fed a diet with higher amounts of dietary C-18 PUFA. In particular, fish receiving high amounts of dietary C-18 PUFA had a greater amount of Delta-6 desaturase activity acting on 18:3n-3 than 18:2n-6. However, with the gradual reduction of dietary C-18 PUFA there was a shift in substrate preference of Delta-6 desaturase from 18:3n-3 to 18:2n-6. This information will provide valuable insight for the implementation of low fish oil diets, which permit the maintenance of n-3 LCPUFA levels in farmed Murray cod.