The feeding behaviour of cultured and wild Atlantic salmon, Salmo salar L., in the Louvenga River, Kola Peninsula, Russia

Abstract

Abstract An underwater survey was conducted in the Louvenga River to investigate the behaviour and distribution of juvenile Atlantic salmon, Salmo salar L., and the adaptation of cultured fish to the natural environment. The food and feeding habits of 34 wild and 44 cultured parr released from the Kandalaksha hatchery were also studied. The cultured salmon fed mostly in the bottom 15 cm of the water column in current velocities of 0.2–0.35 m s−1. In contrast to wild fish, when cultured fish moved away from these areas and into areas with higher current velocities (average speeds of 0.52 m s−1) and lower drift density (2.66 particles m−3), they did not show a tendency to return to slower moving water. The diet of cultured parr was made up of benthic invertebrates (20%), terrestrial insects (32%), and drift items (33%), but these proportions were different in the diet of wild parr (2%, 24%, and 67%, respectively), with drift items predominating. The mean quantity of food per stomach indicated that the wild parr were feeding more actively than cultured parr. Invertebrates made up 3% of items in the drift, with the remaining 97% being exuvia of aquatic and terrestrial insects, algae, and various plant remains. Poor quality food items were found in 13% and 25% of the stomachs of wild and cultured parr, respectively, demonstrating that the cultured parr were less able to differentiate food items in the water column and made 20–30% more false feeding attempts than wild fish. The cultured parr were also more aggressive in terms of the frequency of aggressive interactions and reacted to each other at greater distances than wild fish. Thus, wild parr were able to optimize their feeding conditions by choosing habitats with preferred sizes of food items, higher densities of drift items, and current velocities that allowed them to maintain station and to feed more effectively. Conversely, cultured parr usually occupied suboptimal areas.