Compensatory growth for free?: A field experiment on brown trout, Salmo trutta

Laboratory studies suggest that animals may be capable of compensatory growth after periods of food shortage. There is, however, a lack of field experiments investigating the incidence and consequences of compensatory growth in the wild, and the relevance of compensatory responses in natural populations has recently been questioned. Here we addressed the hypotheses that (1) food restriction during critical growth periods can induce compensatory growth, and (2) that compensatory growth is associated with delayed costs in natural populations. These hypotheses were addressed by (1) manipulating the food intake of brown trout in spring, (2) measuring growth rate responses over the first month following release, and (3) measuring growth and mortality (i.e. recapture rate) over the subsequent fall and winter. We found that brown trout restored lost body weight and condition within a month, providing the first experimental demonstration of compensatory growth in the wild. However, no delayed costs of the compensatory response could be detected within the timespan of the experiment. We suggest that wild brown trout have an adapted buffer capacity to withstand fluctuations in food supply, allowing restoration of lost lipid reserves when feeding conditions improve. However, when prolonged food deprivation affect structural components, compensation may not be possible without compromising long-term performance.