Feeding behaviour, energy expenditure and growth of rainbow trout in relation to stocking density and food accessibility

Abstract

The effect of stocking density on feed intake, feed utilization and feeding behaviour was studied in groups of rainbow trout submitted to different levels of food accessibility. In the first experiment, 18 groups of 100, 300 or 500 fish (initial individual weight 26 + 0.5 g) were held in 1 m 3 tanks where they were fed: in excess using belt feeders; or by means of self-feeders with a fixed reward level (4 g per trigger actuation); or a reward level proportional to fish density (2 g/100 fish/trigger actuation). Final biomass after 125 days was c. 25, 70 and 100 kg/m 3 in groups of 100, 300 and 500 fish respectively. Growth and feed intake was affected by fish density, feeding technique and reward level. However, feed efficiency, body composition, as well as nutrient retention and loss were unaffected by the treatment. In the self-fed groups, daily pattern of feeding activity was affected by fish density when the reward level was fixed but not when the reward level was proportional to fish density. In a second experiment, groups of 100 or 500 fish (same initial individual weight) had access to one or three self-feeders. Access to multiple self-feeders had no positive effect on any of the studied parameters. The fish used only one of the three feeders at a time, and the three feeders where not used equally. We conclude that feed intake but not feed utilization was impaired by increased density, indicating that density in itself is not stressful to the fish. Food accessibility is the main factor responsible for the observed density ± related decrease in growth.

Effect of Stocking Density on Production of <i>Clarias Gariepinus</i> (Tuegels) in Floating Bamboo Cages at Kubanni Reservior, Zaria, Nigeria

“…The cost of production ( Table 4) recorded shows that there was a marginal decrease in terms of profit from 7,969.95 to ₦5,185.80 as the stocking density increased. Values with different superscripts in the same row are significantly different at P 0.05 DISCUSSION Stocking density is one of the main factors determining fish growth (Engle and Valderrama, 2001;Rahman et al, 2005) and the final biomass harvested (Boujard et al, 2002). Identifying the optimum stocking density for a species is a critical factor not only for designing an efficient culture system (Leatherland and Cho, 1985), but also for optimum husbandry practices.…”

Fin condition of fish kept in aquacultural systems

“…Most of publications are focused on Salmonids rearing, mainly rainbow trout. High stocking density over 500 fi sh m −3 limits an access of food to some individuals, it reduce fi sh apetite, infl uences fi sh growth (Boujard et al, 2002) ) than at high stocking density (124 kg.m −3 ). Other subordinate fi sh have mostly damaged dorsal fi ns caused by high ranking individuals and a damage level of dorsal fi ns can be used as social hierarchy indicator inside the fl ock (Moutou et al, 1998).…”

Behavioural indicators of welfare in farmed fish

“…Indirect suggestions come from the effect of stressors on the use of self-feeders. Boujard et al (2002), for example, showed that increased stocking densities of rainbow trout reduced the number of operant tasks (use of self-feeders) executed to obtain a fixed food reward. Other examples, although not in an aquaculture context, come from exposing rainbow trout to noxious stimuli, which has been shown to affect an individual's exploratory behaviour (Sneddon et al 2003).…”