By Peter Landergren
Fisheries Research, Volume 40, Issue 1, 1 February 1999, Pages 55-63, ISSN 0165-7836, DOI: 10.1016/S0165-7836(98)00215-X.

Interference competition for territorial space and food resources between progeny of anadromous brown trout, i.e., sea trout, Salmo trutta L., and non-indigenous anadromous rainbow trout, Oncorhynchus mykiss, was studied in stream channels under laboratory conditions. In addition, the two anadromous species were compared by measurements of fecundity, egg size, alevin size, growth rate, and timing of spawning migration. Competition was mediated through migration of sea trout parr out of the stream channels and the results suggest a negative influence on the sea trout in terms of displacement further downstream in the channels and lowered specific growth rate when fish of equal size were tested together. Given the size advantages normally found, caused by differences in spawning period, sea trout parr held their positions in the stream channels while the smaller rainbow trout parr moved out of the system or stayed in areas where sea trout were absent.
This study was initiated because an increasing number of ascending rainbow trout was reported in many streams on Gotland. Spawning rainbow trout have been observed to have destroyed sea trout spawning redds. Despite rainbow trout spawning in many streams, only one descendant from these anadromous rainbow trout has been found to date.
Keywords: Salmo trutta; Oncorhynchus mykiss; Stream; Spawning; Competition; Interactions

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