The behaviour and the relationship between food intake and growth of juvenile Arctic charr, Salvelinus alpinus L., subjected to sustained exercise JORGEN SCHOU CHRISTIANSEN AND MALCOLM JOBLING Norwegian College of Fishery Science, University of Troms4, 9000 Troms4, Norway Received August 25, 1989 CHRISTIANSEN, J. S., and JOBLING, M. 1990. The behaviour and the relationship between food intake and growth of juvenile Arctic charr, Salvelinus alpinus L., subjected to sustained exercise. Can. J. Zool. 68: 2185-2191. The effects of long-term moderate exercise on the behaviour and the food intake - growth relationship of individually marked Arctic charr, Salvelinus alpinus L., were examined. Direct monitoring of food intake of individual fish was carried out using an X-radiographic method. Growth (weight gain) was significantly improved with increasing swimming speed, and a maximum specific growth rate was obtained at a swimming speed of approximately 1.75 body lengthsls. Growth appeared to be suppressed by high levels of aggressive interactions, and an increase in swimming speed caused a marked increase in schooling behaviour, with a concomitant reduction in agonistic activity. The exercising fish did not consume more food than controls, and moderately exercised Arctic charr showed improved growth - food intake ratios at all levels of food intake compared with fish held in standing water. Furthermore, the proportions of nonfeeding fish were significantly reduced at increasing water velocities. Thus, the relationship between food intake and growth may be strongly influenced by agonistic activity, which appears to be most prevalent in fish subjected to low water velocities. CHRISTIANSEN, J. S., et JOBLING, M. 1990. The behaviour and the relationship between food intake and growth of juvenile Arctic charr, Salvelinus alpinus L., subjected to sustained exercise. Can. J. Zool. 68 : 2185-2191. Les effets d'un exercice modCrC de longue durCe sur les relations entre comportement et nourriture d'une part et croissance d'autre part ont CtC dCterminCs chez des Ombles chevaliers, Salvelinus alpinus L., marquCs. La consommation de nourriture a CtC mesurCe directement par une mCthode radiographique (rayons X). La croissance (augmentation de masse) est significativement plus rapide a une vitesse de nage plus grande et le taux de croissance spCcifique maximal a CtC obtenu a une vitesse de nage d'environ 1,75 longueur totalels. La croissance semble entravCe par des taux ClevCs d'interactions agressives et une augmentation de la vitesse de nage s'accompagne d'une augmentation de la formation de bancs de poissons, ce qui rCduit I'activitC agonistique. Les poissons tres actifs ne consomment pas plus de nourriture que des poissons tCmoins et un exercice moyen rend le rapport croissance - consommation de noumture supCrieur au rapport enregistrC chez des poissons gardCs en eau calme. De plus, la proportion de poissons qui ne se noumssent pas diminue significativement lorsque la vitesse du courant augmente. Les relations entre la consommation de nourriture et la croissance peuvent donc Ctre fortement influencCes par une activitC agonistique, activitC qui semble prCvaloir chez les poissons soumis a une vitesse de courant faible. [Traduit par la revue] Introduction The study of energetics and growth of domestic animals involves both economical and theoretical aspects (e.g., Elliott 1982; Jobling 1985; Reeds 1987), and the elucidation of factors leading to optimalization of growth (weight gain) is an important aspect of salmonid culture. The impact of behaviour on growth has been recognized for several years in the industrialized production of domestic animals such as swine and poultry (Wood-Gush 1971 ), but behavioural studies on salmo- nids in culture ai-e sparse. In their natural environment salmo- nids are active swimmers (Brett and Glass 1973), and the natural swimming behaviour displayed by salmonids may be inhibited when they are kept in captivity at high stocking densities and under poor water-current conditions. Results of several studies have confirmed that moderate sus- tained exercise, as defined by Beamish (1980), leads to increased weight gain in salmonids (e.g., Davison and Goldspink 1977; East and Magnan 1987; Totland et al. 1987; Christiansen et al. 1989; Davison 1989), but in none of these studies was it possible to examine the relationship between food consumption and growth. The basis of any study of energetics and growth is a precise estimate of food intake. In many of the studies carried out on fish, however, the amount of food offered to the fish is assumed to equal actual food intake (e.g., Wurtsbaugh and Davis 1977), and this assumption means that realistic assess- ments of the food intake - growth relationship are precluded. Even when all food offered is consumed, there is often no information available as to amounts of food consumed by indi- vidual fish within a rearing group. Consequently, food intake and growth of individuals within groups have rarely been studied (Jobling et al. 1989). The purpose of the present study was to estimate the effects of sustained exercise on the behaviour and food intake - growth relationship of Arctic charr (Salvelinus alpinus L.), and an X-radiographic method was used to determine food intake by individual fish (Talbot 1985; Jobling et al. 1989). Since changes in environmental conditions may induce changes in behaviour of salmonids kept in captivity, observations were carried out to determine the potential impact of behavioural interactions on the food intake - growth relationship of groups of fish subjected to different levels of sustained exercise. Materials and methods Fish used in the experiment were hatchery-reared Arctic charr parr (Salvelinus alpinus L.) of the Hammerfest strain. Approximately 3 months prior to the start of the experiment, fish were individually tagged with FTF-69 fingerling tags (Floy Tag & Mfg.) sewn just beneath the anterior cartilage of the dorsal fin. At the start of the experiment the average live weight and fork length of the fish (500 individuals) were approximately 20 g and 13 cm, respectively. The fish were divided randomly into five treatment groups (two tanks per group). Each centrally drained circular tank (fresh water volume 80 L) contained 50 individuals (Fig. I). The fish were subjected to different levels of sustained exercise by being forced to swim against water currents of different velocities. Water velocities were measured weekly at points shown in Fig. 1, using an anemometer (TAD Hontzsh GmbH, measurement range 0.04- 10 m s- I), and water-exchange rates were identical for all tanks (15 L min-I). Cur- rents were created by forcing the water through vertically mounted perforated inlet pipes. Control groups of fish were held in tanks equipped Printed in Canada 1 Imprim6 au Canada Can. J. Zool. Downloaded from www.nrcresearchpress.com by Universitetsbiblioteket i Tromsoe on 01/27/14 For personal use only.