Gill tissue lipids of salmon (Salmo salar L.) presmolts and smolts from anadromous and landlocked populations

Composition of membrane lipids from the gills of juvenile Atlantic salmon (Salmo salar) in presmolt and smolt phases of development was compared among anadromous and non-anadromous populations. Three stocks migrating from spawning rivers to either lake (landlocked stock), brackish water or full strength sea water were grown under common garden conditions, and gill lipids and their acyl and alkenyl chains were examined in February (presmolts) and at the end of May (smolts) by mass spectrometry and gas-liquid chromatography. The most remarkable changes upon transition from the presmolt phase to the smolt phase were: (i) increase in the cholesterol/phospholipid ratio, (ii) decrease in the abundance of phosphatidylinositol (PI) content, (iii) increase in the amount of sulfatides, (iv) increase in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) species with two highly unsaturated acyl chains, and finally (v) convergence of interstock differences in PC and PE species composition towards a similar lipid composition. Increases in the gill membrane content of cholesterol and sulfatides are discussed as pre-adaptation of salmon gills for salt-secretion, which may occur by increases in membrane microdomains (rafts) harboring ion channels and pumps. The decreases of PI were likely related to adjusting the gill membrane permeability to ions by diminishing prostanoid production. The similarity of those changes among three salmon stocks and the convergence of initially (presmolt phase) different PC and PE species profiles between the stocks towards similar lipid composition suggests that smoltification process of the gill epithelium is largely similar in anadromous and landlocked populations.