Investigating the Effect and Relationship of Life-History Genetics and Population Density on Juvenile Atlantic Salmon (Salmo salar) Food Acquisition

Life-history decisions, and trade-offs, are affected by resource acquisition, which can vary among individuals, and during the life cycle of an individual. In Atlantic salmon (Salmo salar) many life-history decisions, such as age-of-maturity, are strongly associated with two genomic regions, vgll3 and six6. Previously, these genomic regions have been associated with food acquisition in adult sea-run Atlantic salmon; however, this has not yet been studied in juvenile salmon. Furthermore, population density strongly affects the food availability of juvenile salmon through resource competition. Here, using controlled crosses reared in semi-natural stream conditions, I investigated the effect and relationship of life-history genetics and population density on juvenile Atlantic salmon food acquisition. Stomach contents from 148 juvenile Atlantic salmon were quantified for their prey item composition, total number of prey items and dry weight, and environmental and genetic basis of food acquisition were analysed using mixed effects models. Late maturing six6 genotype fish had higher stomach-content dry weights and fuller stomachs than early maturing individuals, in low densities. Furthermore, low density fish were of better condition and had higher growth rates than high density fish. There was no association between six6 and vgll3 genotypes and food acquisition in high densities. The results support the existing knowledge of the negative effect of increasing population density on juvenile Atlantic salmon growth and condition. Furthermore, the density dependent association of six6 and food acquisition suggest a trade-off between early maturation and maximised food acquisition