Handling and stocking-density effects on growth rhythms of brook trout, Salvelinus fontinalis

We evaluated the effects of handling and stocking density (3 vs. 6 fish/150 L) on the growth-rate rhythms of brook trout, Salvelinus fontinalis. The length of nonhandled fish was estimated with a stereo-video technique and the length and mass of handled fish was measured directly. The main effects of handling and stocking density and their interactions on growth rates were not statistically significant, whereas the main effects of time were significant, as shown by repeated measure analysis. Multifrequential periodogram analysis indicated significant infradian rhythm components of about 8 d in the relative growth rate in length and of about 5 and 11 d in the relative growth rate in mass, regardless of the treatment applied. The characteristics (period, amplitude, and phase) of the rhythms found were not altered, either by handling or by stocking density.