Buoyancy Comparisons between Juvenile Atlantic Salmon and Brown Trout of Wild and Hatchery Origin

Abstract

Buoyancies of juvenile Atlantic salmon Salmo salar and brown trout Salmo trutta were examined, as differences may influence stream distribution and feeding habits of these species. Among age-0 and age-1 fish living and tested in moving water, hatchery-reared Atlantic salmon were less buoyant than brown trout. After four days in still water, Atlantic salmon had increased their buoyancy to the point that age-0 (but not age-1) fish were as buoyant as comparably aged brown trout. In streams, low buoyancy would help Atlantic salmon to stay near the substratum where water velocity is less. This would enable them to inhabit areas of higher velocity than brown trout. Body density, and swim-bladder length and weight, did not appear related to buoyancy differences between species. Among brown trout, hatchery fish were more buoyant than wild fish, possibly due to differing diets (especially lipid contents) or to genetic differences.