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

Abstract

In intensive rearing systems, increasing fish stocking density is one way to 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 (increased social interactions, aggression or chasing), which generate supplementary 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 bioenergetic significance of the density-dependent changes in RMR, we estimated the animals metabolic scope. Respirometry experiments were conducted at three densities: 25, 65 and 100 kg m −3 using 11°C-acclimated starved individuals (261±5 g). In our experimental conditions, no significant variations of RMR were detected between 25, 65 and 100 kg m −3. Aerobic metabolic scope was estimated at 285 mg O 2 kg −1 h −1. When analysed with regard to metabolic capacities, RMR amounted to less than 15% of fish metabolic scope. Furthermore, at all densities the RMR diel cycle was preserved and inter-groups variability in RMR was highly significant, reinforcing the idea that density was not a determinant factor of the rainbow trout RMR in our experimental conditions.