Impact of macroinvertebrate diet on growth and fatty acid profiles of restocked 0+ Atlantic salmon (Salmo salar) parr from a large European river (the Allier)

The influence of macroinvertebrate diet on growth and fatty acid profiles of Atlantic salmon ( Salmo salar ) parr released at the fry stage in three different riffles was studied in a large temperate river (Allier, France). Comparisons were made between sites and between restocked parr and hatchery-reared counterparts fed with a traditional fish diet. Significant differences were observed along the longitudinal gradient of the river and between restocked and hatchery-reared parr. Growth performance and nutritional status were higher in the hatchery and in downstream riffles and low in the most upstream site. These differences appeared to be related to different types of diet and consequently to variations in polar and neutral lipid intakes. The most favorable site for optimum growth appeared to be the intermediary riffle, with values close to those achieved in the hatchery. Simuliids and baetids, preferentially consumed in downstream sites, constitute an interesting type of food, showing quite different fatty acid composition from vegetable oils. This could be of interest for composing a new diet formula for young salmon intended for river restocking, imitating these macroinvertebrate fatty acid profiles.