Fatty acid and lipid class composition in eyes and brain from teleosts and elasmobranchs

The fatty acid and lipid class composition of the eyes and brain were determined for the following species: Atlantic cod (Gadus morhua), saithe (Pollachius virens), redfish (Sebastes marinus), Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), Portuguese dogfish (Centroscymnus coelolepis), black dogfish (Centroscyllium fabricii), and leafscale gulper shark (Centrophorus squamosus). Fatty acid analyses of eyes from teleosts in the present study indicated that the lean species contained high ratios of docosahexaenoic acid (DHA) versus eicosapentaenoic acid (EPA), and high ratios of n-3 fatty acids versus n-6 fatty acids, while these ratios were significantly lower for the fatty fish species. The lipid class analyses revealed that among both elasmobranchs and teleosts, phospholipid was the dominant class of lipids in the eyes of lean species, while triacylglycerol was the dominant class of lipids in fatty species. Analyses of the fatty acid composition of brains revealed that the deep-sea elasmobranchs, Portuguese dogfish, black dogfish, and leafscale gulper shark, contained a level of arachidonic acid (AA) that was higher than their level of EPA and about fivefold higher than what was found in the brains of teleosts. Such high levels of AA are not normally observed in fish brains; rather, they are generally observed in brains of higher vertebrates.