Influence of fish density on the energy allocation pattern of juvenile brook trout (Salvelinus fontinalis)
Our objectives were (i) to assess the influence of fish density on the energy allocation pattern of juvenile brook trout (Salvelinus fontinalis) and (ii) to define the mechanism by which this influence occurs. We estimated growth, consumption, and activity rates of brook trout held in 8-m3 enclosures characterized by two different densities (four or eight fish per enclosure; D4 and D8 enclosures, respectively). Eight experiments designed to estimate these variables were performed during a 27-day period. Fish from D4 enclosures ( DELTA W bar = 0.46 g) grew twice as much as those from D8 enclosures ( DELTA W bar = 0.24 g). For any given experiment, consumption rates were not significantly different between the two fish densities (0.434-1.09 g dry ·100 g wet-1 ·day-1). However, fish stocked in D8 enclosures displayed more aggressive behavior, executed 5.5 times more movements, and swam at speeds 13% faster than fish in D4 enclosures. These differences resulted in activity rates fourfold higher in D8 enclosures than in D4 enclosures. Empirical analyses combining our results with published values of growth, consumption, and activity rates supported the hypothesis that competition can have a negative effect on growth through a decrease in consumption rates and an increase in activity costs.