Effects of dichlorvos and formalin on fatty acid metabolism of rainbow trout (Oncorhynchus mykiss) skin cells in primary culture

Abstract

The effects of sub-lethal doses of dichlorvos and formalin, antimicrobial/parasitic agents used in aquaculture, on lipid composition and metabolism of rainbow trout skin cells in primary culture were investigated. [1-14C]Stearic (18:0), [1-14C]linoleic (18:2n-6) and [1-14C]linolenic (18:3n-3) acids were used as tracers to determine effects on fatty acid incorporation and metabolism. Formalin increased cell numbers and reduced the lipid content of the cells and the incorporation of radioactive fatty acids. The effects of dichlorvos were qualitatively similar but quantitatively less. Formalin induced relatively small but significant changes in lipid class composition including a decreased proportion of phosphatidycholine with increased proportions of phosphatidylethanolamine and phosphatidylserine. Dichlorvos had no significant effect on lipid class compositions. The trout primary skin cells expressed substantial Δ9, Δ6 and Δ5 fatty acyl desaturase activities. Although, as expected, the cells were more active towards [1-14C]18:3n-3, the cells were unusually active towards [1-14C]18:2n-6. Both dichlorvos and, especially, formalin appeared to significantly inhibit Δ9 and Δ6 desaturase. Changes in the distribution of radioactivity between individual phospholipid classes was also influenced by formalin and dichlorvos, and this may be related to changes in desaturase activity. This study has shown that topically active agents used in aquaculture, formalin and dichlorvos, had a range of effects on the rainbow trout skin cell cultures that may affect cell proliferation and lipid and fatty acid metabolism. Both agents significantly inhibited desaturation of fatty acids, particularly of 18:2n-6 to 20:4n-6 and, as 20:4n-6 is a major eicosanoid precursor in fish and considering the importance of eicosanoids in the biochemistry of skin ,it is suggested that these agents may have direct effects on fish skin that may have important consequences for fish health in general.