Pre-winter lipid stores in brown trout Salmo trutta along altitudinal and latitudinal gradients.

Pre-winter lipid stores of brown trout Salmo trutta L. parr were compared along altitudinal (0-920 m a.s.l.) and latitudinal (58-71° N) gradients. There were increases in lipid content (size adjusted to common lipid-free dry mass of 2·0 g, corresponding to fresh mass of 10 g) with both increasing altitude and latitude. Mean size-adjusted lipid content for S. trutta in high altitude rivers was 60% higher than at low altitude (0·29 and 0·18 g, respectively). Mean size-adjusted lipid content for S. trutta in northern rivers was 30% higher compared to that in southern rivers (0·30 and 0·23 g, respectively). There was a marked between-river variation in mean lipid storage, probably reflecting different strategies or opportunities for the pre-winter acquisition of lipid both locally within rivers and between different populations. This study shows that temperature or winter length, not latitudinal covariates such as annual light regime, governs lipid storage patterns in juvenile salmonids.