Fixing fish brains in paraformaldehyde solution in order to do morphological measurements prevented us from performing fatty acid analysis of the brain tissue. Therefore, we have used the muscle tissue as a proxy of n-3 LC-PUFA content in fish body. Muscles provide a good proxy for this purpose, because they represent the majority of fish biomass, and thus muscle metabolic activity and fatty acids content reflects individuals as a whole (Norin & Malte 2012; Gladyshev et al. 2018). In addition, biochemical composition of muscle tissue of salmonids has been shown to respond in similar direction to dietary deprivation of n-3 LC-PUFA as brain tissue, but with higher magnitude (Závorka et al. 2021). Thus, samples (~1 g of wet mass) of dorsal and ventral muscle tissue samples were taken from the left side below the dorsal fin, above and below the lateral line respectively. Bones and skin residuals were mechanically removed from the tissue samples, before they were stored on dry ice and subsequently frozen at -80 °C.