Camp. Eiochem. Physiol. Vol. IOIA, No. 2, pp. 369-374, 1992 0300-9629/92 WI0 + 0.00 Printed in GreatBritain 0 1992 Pergamon Press plc zyxwvuts COMPARATIVE NUTRITION PAPERS FEED UTILIZATION EFFICIENCIES OF ATLANTIC SALMON (SALMO SALAR L.) PARR: EFFECT OF A SINGLE SUPPLEMENTARY ENZYME C. G. CARTER, D. F. HOULIHAN and I. D. MCCARTHY Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen AB9 2TbJ, U.K. Telephone: (0224) 272867; Fax: (0224) 272396 zyxwvutsrqponmlkjihgfedcbaZYX (Received 22 July 1991) Abstract-l. Salmon Salmo s&r parr were fed three rations of a control diet and one ration of a diet containing a supplementary enzyme, K-amylase. 2. X-Radiography was used to estimate the consumption rates of individual fish. 3. Consumption-growth relationships for wet weight, dry weight, nitrogen and carbon were established for the two diets. 4. The supplementary enzyme had no statistically significant effect on the consumption-growth relationships or feed utilization efficiency. INTRODUCTION Much of the research on the growth of fish is motivated by the desire to establish which con- ditions promote the most efficient growth. On a commercial level, the primary aim is to maximize growth and survival at minimum cost (Knights, 1985) and improvements in food utilization efficiencies are one way to achieve this. Supplementary hydrolytic enzymes have been successfully added to pig and poultry diets (Collier and Hardy, 1986; Inborr, 1990). These are intended to act whilst in the digestive tract and improve dietary utilization by increasing digestion efficiencies and thereby increasing growth efficiency. Supplementary enzymes have received little attention in fish nutrition and most studies have concentrated on larval diets (Dabrowska et al., 1979; Uys et al., 1987; Munilla-Moran et al., 1990). Food consumption rates are a major influence on growth rates and have usually been investigated on individual fish fed known rations (e.g. Solomon and Brafield, 1972; Flowerdew and Grove, 1981; Cui and Wootton, 1988) or on groups fed a range of rations (e.g. Elliott, 1976; Huisman, 1976; Store- bakken and Austreng, 1987a,b). Although well estab- lished and useful in many ways these approaches may present some problems with some species. Naturally gregarious fish such as the salmonids may not feed normally when kept individually. The individual con- sumption rates of fish maintained in groups are not known which makes it difficult to calculate individual growth efficiencies. To overcome these problems several non-destructive methods to assess individual consumption rates have been used with groups of fish (e.g. Storebakken el al., 1981; Talbot and Higgins, 1983; Jobling et al., 1989; Kadri et al., 1991). The use of reliable estimates of individual consumption rates has great protential for use in growth studies since it allows feeding patterns in individual fish to be monitored. The analysis can be extended to the construction of elemental budgets (e.g. nitrogen, carbon and phosphorus) and calcu- lation of growth efficiency. The aims of this study were to investigate the consumption, growth and retention efficiencies of individual salmon Parr. The approach was adopted to assess the feasibility of adding enzymes to pelleted diets in order to increase feed utilization efficiency. MATERULS AND METHODS Animals Salmon parr (Clone Hatcheries, Auchterarder) were ran- domly distributed in circular fibre glass tanks containing 390 dm3 of water to which fresh water was added at a rate of approximately 50 dm’/hr. The fish were left to acclimate for several weeks while fed daily on salmon fingerling diet (North Eastern Farmers Ltd). At the start of the experiment the fish were not fed for two days, anaesthetixed in MS-222 (0.1 g/dm3), weighed and individually marked with alcian blue. Four groups of 30 fish were returned to the tanks and the experimental feeding regimes started on the following day. At the same time 12 fish were placed in another tank and left without food for 30 days. A further 10 fish were selected as an initial control and were killed, weighed and frozen at -70°C until analysed. Diets and feeding A standard diet and a test diet, the standard diet plus a commercial amylase preparation (approximate activity __ added per gram of food:. 2.9 mg maltose liberated from starch ner min at 20°C at PH 6.9) were nrenared (Table 1). Pellets bf 2.4 mm diameter-were produced \;ith a t&for& pellet mill. The fish were fed once a day over an extended period of 30 min by dropping single pellets into the tanks until either all the pellets had been eaten or the last pellet to be supplied was not eaten. The standard diet was fed at three ration ceP(A) 101:2-n 369