Behavioural responses of salmonid fry to low amino acid concentrations

The behaviour of start feed brown trout, Salmo trutla , and Atlantic salmon, Salmo salar , fry was observed in response to 5, 50 and 500 nM concentrations of L‐alanine, L ‐proline, L‐arginine and glycine. In addition, salmon fry were tested with dilute concentrations of shrimp extract. Five behaviour patterns (snap, yawn, dart, twitch movements and active swimming) were shown in response to all amino acid and shrimp extract concentrations. Snapping, darting and active swimming increased in both species as a function of amino acid concentration, and in the salmon fry as a function of increasing shrimp extract concentration. Otherwise, the salmon showed twice as much yawning and more twitch movements than the trout, but the trout showed more active swimming than the salmon. Both species showed an increase in activity in response to L‐proline at 5 nM, and the salmon also responded to L‐arginine and glycine at this concentration. Both species first responded to L‐alanine at 50 nM, but the trout did not respond to glycine until a concentration of 500 nM was presented. The salmon fry responded to shrimp extract at c. 10 14 g l ‐1 , but no differences in their activity were observed in response to concentrations between c. 10 ‐12 and 10 ‐6 gl ‐1 .