Modelling growth and food intake rhythms of brook trout Salvelinus fontinalis under the effects of density and ration

We previously found short periodicities of 4–10 days in the relative growth rates in length and in mass of brook trout Salvelinus fontinalis that persisted under constant lab conditions as well as under different levels of stocking density, food ration and handling. In this experiment, we used the multifrequential periodogram analysis and ANOVA of finite Fourier transform to study growth rates and food intake under different levels of stocking density (1.52 kg m−3 versus 0.76 kg m−3) and ration (1.25% versus 2.5%). We found significant periodicities: 4–6 days in growth rate in length, and 5–10 days in mass respectively explaining 82 and 80% and of the total variation. We also found that daily food intake did not follow the same rhythmic patterns as growth rate with periodicities of 6 and 20 days explaining 91% of the total variation. Stocking density and ration level significantly affected daily food intake but not growth rate rhythms. We developed a system of trigonometric functions of time in days that incorporated significant frequencies estimated by the multifrequential periodogram. The models captured the short-term temporal variations of relative growth rates and daily food intake of young-of-the-year (YOY) brook trout and accounted for the effects of in food ration and stoking density. The models also predicted the relative growth rates and daily food intake with a Rpred2 varying from 73 to 93%. Our findings could improve our understanding of the dynamics in growth rates and food intake of fish populations in natural environments and could have practical consequences for the design of growth experiments and pisciculture.