Stock-Specific Growth and Length Frequency Bimodality in Brown Trout

Abstract

The growth of three pure stocks and one hybrid stock of anadromous brown trout Salmo trutta—comprising 19 families and 15,000 individuals—was monitored under controlled conditions from hatching for a period of 16 months. Significant differences in growth were detected among the three pure stocks, and the hybrid stock outgrew its two parental stocks. Significant differences in family growth were also detected. Two of the stocks developed clear bimodal length frequency distributions, whereas the other two stocks displayed skewed or weakly bimodal length frequency distributions. The observed differences in growth among the stocks probably reflect genetic differences in growth potential. The pattern of growth and development of length frequency bimodality in the brown trout stocks reared in this study is similar to the pattern of growth and length frequency bimodality development in Atlantic salmon Salmo salar. We conclude that length frequency bimodality in anadromous brown trout is probably linked to the process of smoltification, as is the case for Atlantic salmon.