Effect of density on the routine metabolic expenditure of farmed rainbow trout (Oncorhynchus mykiss)

In intensive rearing systems, increasing fish stocking density is one way t o optimize productivity. However, high rearing density is also a potential source of stress that may constrain fish growing capacity. This detrimental effect on growth is partly mediated through behavioural alterations (incre ased social interactions, aggression or chasing), which generate supplement ary metabolic expenditure and most likely alter feeding behaviour. In this study, we examined the effects of rearing density on the routine metabolic rate (RMR) of rainbow trout. Concurrently, and in order to determine the bi oenergetic significance of the density-dependent changes in RMR, we estimat ed the animals metabolic scope. Respirometry experiments were conducted at three densities: 25, 65 and 100 kg m(-3) using 11 degreesC-acclimated starv ed individuals (261 +/- 5 g), In our experimental conditions, no significan t variations of RMR were detected between 15, 65 and 100 kg m(-3). Aerobic metabolic scope was estimated at 285 mg O-2 kg(-1) h(-1). When analysed wit h regard to metabolic capacities. RMR amounted to less than 15% of fish met abolic scope. Furthermore, at all densities the RMR diel cycle was preserve d and inter-groups variability in RMR was highly significant, reinforcing t he idea that density was not a determinant factor of the rainbow trout RMR in our experimental conditions. (C) 2001 Elsevier Science B.V. All rights r eserved.