Aquaculture International 6, 95–102 (1998)
Influence of dietary fat level on feed intake, growth and fat deposition in the whitefish Coregonus lavaretus J. Koskela1, M. Jobling2,* and R. Savolainen1 1
Finnish Game and Fisheries Research Institute, FIN-41360 Valkola, Finland Norwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway 2
Whitefish, Coregonus lavaretus, of initial mean weight 260–265 g were fed either a high-fat or a low-fat diet (dietary fat: 27.5% vs. 12.6%) to examine the influence of dietary fat level on feed intake, growth and patterns of fat deposition. The fish were held at 14.5 °C under a 24L:0D photoperiod, and were fed for 4 h each day. The experiment was run for 11 weeks during which feed intake (three times by X-radiography) and growth were monitored. Samples of fish were taken for body composition analysis at the start and end of the experiment. There were only small differences between dietary treatment groups in feed intake and final body weights, but the body composition of the fish was significantly influenced by the fat content of the diet. The whitefish fed the high-fat diet tended to have higher relative fat contents in the viscera [% fat as mean (SD): 29.6 (9.4)% vs. 22.1 (10.0)%] and carcass [% fat: 12.7 (1.9)% vs. 10.5 (1.3)%] than their counterparts fed the low-fat diet. This resulted in a higher whole-body fat concentration [% fat: 14.0 (1.9)% vs. 11.5 (1.5)%] amongst the fish fed the high-fat diet, and these fish had a higher energy gain than the whitefish fed the low-fat diet. The results confirm that it is possible to manipulate the chemical composition of whitefish by changing dietary composition. KEYWORDS: Coregonids, Daily ration, Fat deposition, Growth, Whitefish (Coregonus lavaretus)
INTRODUCTION Coregonids are popular food fishes in several northern and eastern European countries, and juvenile whitefish are reared for stock enhancement purposes (J¨arvinen, 1988; Todd and Luczynski, 1992; Luczynski et al., 1995). In recent years attention has been directed towards intensive production methods, but information about the growth and nutritional requirements of larger fish in culture is limited (Koskela, 1992, 1995; Todd and Luczynski, 1992; Luczynski et al., 1995). It is well known that growth and chemical composition of fish can be influenced by dietary manipulation (Reinitz, 1983; Shearer, 1994), and there is increased interest in devising methods for the control of chemical composition and food quality attributes of farmed fish (Haard, 1992; Wathne, 1995). Consequently, the influence of dietary fat level on feed intake, growth and energy deposition has been examined in * Author to whom correspondence should be addressed (e-mail:
[email protected]). 0967–6120 © 1998 Chapman & Hall
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whitefish, Coregonus lavaretus, to obtain information that may assist in the development of feeding practices for this species in culture. MATERIALS AND METHODS The growth trial was carried out between 28 June and 11 September 1996 at the Laukaa Research Station of the Finnish Game and Fisheries Research Institute (62°30'N, 26°E). The fish used were 21hatchery-reared whitefish of initial weight about 265 g (Table 1). At the start of the experiment, a subsample of 10 fish was taken for analysis of body composition. Experimental groups, two per dietary treatment, were established by transferring 60 fish to each of four 4 m2 hatchery tanks (volume: 1.2 m3), such that the mean weights of fish within each tank were within the range 260–265 g (Table 1). The rearing tanks were supplied with freshwater (approx. 14.5 °C; range 14–15.7 °C) flowing at a rate of 14 l min–1. Fish were exposed to continuous light provided by lamps in the roof of the rearing hall, and feed was supplied for 4 h per day, in the period 0800–1200 h, using belt feeders. The fish were fed on either a commercial dry pellet (Ewos Vextra Elips; composition: protein, 50.3%; fat, 27.5%; energy, 24.4 kJ g–1), or this feed without the fat top dressing (composition: protein, 59.1%; fat, 12.6%; energy, 21.2 kJ g–1). Diets used for feed intake measurement were prepared from subsamples of the high- and low-fat feeds by grinding, homogenization and incorporation of known quantities of X-ray-dense ballotini glass beads (Jencons Ltd, Leighton Buzzard) followed by compression into pellets and re-drying at 40–45 °C. Standard curves were then prepared by weighing small subsamples of the marked feed, taking an X-ray photograph, and counting the numbers of ballotini on the developed plate. The marked high-fat feed was prepared using ballotini size 10, and gave the following standard curve: Feed (g) 5 0.023 Ballotini – 0.096 (n 5 16; r2 5 0.93; p , 0.001)
(1)
whereas size 8.5 ballotini were used for preparation of the marked low-fat feed, and the standard curve for this feed was: Feed (g) 5 0.021 Ballotini – 0.074 (n 5 16; r2 5 0.92; p , 0.001).
(2)
All feeds were stored at 5 °C prior to use. Feed intake was measured by X-radiography (Talbot and Higgins, 1983; Jobling et al., 1993) three times during the course of the experiment (on 30 July, 26 August and 11 September). Following the termination of the feeding session with marked feeds, the fish were anaesthetized (MS-222), X-rayed (Siemens Nanodor X-ray machine, Agfa Structurix D7 film) and weighed to the nearest 0.1 g. X-ray plates were then developed and the amounts of feed consumed estimated from the numbers of ballotini present in the gastrointestinal tracts of the fish. Feed intake and weight data were then used to calculate tank means, giving a single value for each replicate within a dietary treatment (n 5 2). At the end of the growth trial, subsamples of fish (five fish per tank) were taken for analysis of body composition. Fish were dissected, and then the viscera and carcass were analysed separately. Samples were first dried for 24 h at 105 °C and then
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ground to a fine powder. Subsamples were then taken for the analysis of fat (by petroleum ether/ether extraction) and energy content (by adiabatic bomb calorimetry). The contribution of fat to body energy stores was estimated using the calorific coefficient 38 kJ g–1 (Jobling, 1994). Statistical analyses were performed using SYSTAT statistical software (SYSTAT, 1996), with possible differences among treatments and groups being tested by ANOVA (Sokal and Rohlf, 1995). Where appropriate, arcsin transformations of data were performed prior to the carrying out of statistical tests, and p , 0.05 was taken as the level of significance. RESULTS The relative feed intakes (g kg–1 d–1) of the groups of whitefish fed the two diets were similar, although towards the end of the experiment there was a trend towards greater consumption by the fish fed the low-fat diet (Table 1). Although no significant differences in feed intake were recorded on any of the three sampling dates, there was an overall indication of a higher energy intake amongst the fish fed on the high-fat diet (Table 1). Any differences in energy intake might have been expected to result in differences in growth and fat deposition. Although the statistical analyses of the weight data failed to reveal significant differences between treatments, there was a trend towards higher rates of growth in the groups of fish fed the diet with the higher fat content (Table 1), a trend that was reflected in the final weights of the fish (treatment means (SD); n 5 2: 512.4 (20.0) g vs. 458.5 (15.5) g for the fish on the high- and low-fat diets, respectively). Dietary treatment had a more marked influence on the chemical composition of the body (Table 2) than upon changes in body mass. When fish were sampled at the end of the experiment, the whitefish fed the high-fat diet tended to have higher proportions of fat in both the viscera and carcass that those fed the low-fat diet. This resulted in a significantly higher percentage of whole-body fat amongst the fish
TABLE 1. The efect of dietary treatment (27.5% vs. 12.6% fat) on feed intake and growth of whitefish. Data for each dietary treatment are presented as tank means (SD), with two tanks per treatment. There were no significant differences between treatments in either feed intake, or fish weights on any of the sampling dates
Sampling date
Treatment
Weight (g)
Intake (g kg–1 d–1)
Intake (kJ kg–1 d–1)
28 June
High fat Low fat
262.5 263.0
30 July
High fat Low fat
360.1 (9.9) 323.9 (6.7)
7.6 (1.8) 6.0 (1.4)
185 (45) 127 (30)
26 Aug.
High fat Low fat
463.0 (41.2) 415.8 (21.4)
3.5 (2.7) 5.5 (0.8)
86 (67) 118 (16)
11 Sep.
High fat Low fat
512.4 (20.0) 458.5 (15.5)
5.2 (0.5) 5.4 (1.5)
126 (12) 114 (33)
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TABLE 2. Initial and final proximate body composition of whitefish fed diets of different fat contents (27.5% vs. 12.6%). Data are presented as means (SD, n 5 10). Differences between treatments are indicated by n.s., not significant; *, p , 0.05; and **, p , 0.01 Final samples
Whole fish % Fat % Moisture Energy (kJ g–1) Viscera % Fat % Moisture Energy (kJ g–1) Carcass % Fat % Moisture Energy (kJ g–1)
Initial
High fat
Low fat
p
12.3 (1.9) 66.9 (2.4) 9.1 (0.9)
14.0 (1.9) 64.6 (3.4) 9.8 (1.1)
11.5 (1.5) 67.2 (1.4) 8.9 (0.5)
** * *
26.9 (9.4) 56.8 (6.3) 13.9 (3.1)
22.1 (10.0) 60.1 (7.4) 12.6 (3.3)
n.s. n.s. n.s.
12.7 (1.9) 65.4 (3.7) 9.4 (1.2)
10.5 (1.3) 67.8 (1.4) 8.5 (0.5)
** n.s. *
FIG. 1. The relationship between percentage fat and percentage moisture in Coregonus lavaretus fet diets of different fat content (dietary fat: 27.5% vs. 12.6%).
fed the high-fat diet, and the differences were reflected in differences between the dietary groups in tissue energy concentration (Table 2). When the body composition data of individual fish were considered, there was an inverse relationship between percentage fat and percentage moisture (Fig. 1): % Fat 5 55.85 – 0.648 % Moisture (n 5 30; r2 5 0.784).
(3)
The body composition data of the initial and final samples of fish (Table 2) were
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combined with the weight data (Table 1) for calculation of the contribution of fat (using the calorific coefficient of 38 kJ g–1) to the absolute amounts of energy in the bodies of the fish at the start and end of the experiment (Fig. 2A). Results of these calculations were, in turn, used to assess the contribution of fat to energy gain during the course of the experiment (Fig. 2B). There was an increase in both fat and total body energy content in both treatment groups during the experiment (Fig. 2A), although the relative contribution of fat to total energy differed between treatments and sampling times. In the initial sample, energy from fat accounted for 51.5% of the total body energy: by the end of the experiment, fat accounted for 54.3% of body energy content of the fish fed the high-fat diet, and 49.1% of the energy content of those fed the low-fat diet. These differences were a clear reflection of differences in the composition of the gain (Fig. 2B), fat accounting for 56.7% of the energy gain in
FIG. 2. (A) Body energy contents, and (B) contributions of fat energy to total energy content and energy gain, in Coregonus lavaretus fed diets of different fat content (dietary fat: 27.5% vs. 12.6%).
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the fish fed the high-fat diet, whereas fat represented only 45.5% of the energy gain of the fish fed the low-fat diet. DISCUSSION Animals usually respond to a dietary dilution, or to being fed low-energy diets, by increasing feed consumption (Grove et al., 1978; Pi-Sunyer, 1990; Boujard and M´edale, 1994; Leeson et al., 1996, a,b), apparently in an attempt to maintain nutrient, or energy, intake. This type of response was not obvious in the current study, whitefish fed the high- and low-fat diets consumed approximately equal quantities of feed (Table 1). It is possible that the restricted time over which feed was available (4 h each day) prevented the fish from consuming more of the low-fat diet to compensate for the low energy content. Results from previous studies suggest there may be an initial period of reduced feed intake following the imposition of a timerestricted feeding regime, although with time animals may be able to compensate for the reduced length of the daily feeding period by increasing their capacity to feed at times when feed is available (Alan¨ar¨a, 1992; Boujard et al., 1996). There was, however, some indication of a possible compensatory response in the study with whitefish, because the difference in feed energy intake noted early in the experiment tended to disappear with the passage of time (Table 1). Body composition was significantly influenced by dietary treatment; percentage fat was higher and percentage moisture lower in the tissues of the fish fed the highfat diet (Fig. 1; Table 2). These differences were particularly obvious in the carcass, although the whitefish fed the high-fat diet also tended to have viscera with a higher percentage fat than the fish fed the low-fat diet (Table 2). Koskela (1995) reported that the viscerosomatic indices of juvenile whitefish fed on diets containing 28–31% fat were higher (VSI 5 8.0–8.8%) than those of fish fed on diets of lower fat content (Dietary fat 17–20%; VSI 5 7.3–7.6%), and the groups of fish fed the high-fat diets also tended to have higher whole-body fat contents than did those fed on the low-fat diets. Muscle fat was, however, little influenced by dietary composition in that study (Koskela, 1995). The results of the present experiment (Fig. 1; Table 2) are in general agreement with several previous reports that the feeding of high-fat diets tends to result in a ‘fattier’ fish (Haard, 1992; Hillestad and Johnsen, 1994; Koskela, 1995; Wathne, 1995), although other workers have indicated that the observed differences in fat content may be more a result of differences in growth rates and fish sizes, than effects of dietary fat content per se (Shearer, 1994; Einen and Roem, 1997). Thus, deposition of body fat may be influenced by factors other than dietary composition: percentage body fat tends to increase with increasing fish size, and with increasing feed supply (Reinitz, 1983; Shearer, 1994; Wathne, 1995). Consideration should also be given to the protein:energy ratio (DP:DE) of the diet (Einen and Roem, 1997), and Koskela (1995) reported that there were significant negative relationships between dietary DP:DE and both VSI and percentage body fat in whitefish. It may often be difficult to obtain clear evidence of changes in body composition induced by dietary treatments, and influences of dietary manipulation are much more likely to be manifest in analyses of the composition of tissue gain than in analyses of relative body composition. Unfortunately, such analyses (Fig. 2) are rarely undertaken, and it is possible that the dietary influences on body
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composition may be either underestimated, or even missed, if data are presented only in terms of the relative proportions of the different tissue components. The body composition data obtained from the whitefish sampled at the end of the present study fit the general pattern reported for dietary influences upon body composition of fish species: the whitefish provided with the high-fat diet were those that had the highest body fat content (Table 2), they had gained most in body mass and energy content (Table 1; Fig. 2B), and they were also those fish that had the lowest percentage body water (Table 2; Fig. 1). CONCLUSIONS 1. Although there were only minor differences in growth between the groups of whitefish fed on the high- and low-fat diets, diet had marked effects upon the chemical composition of the body tissues. 2. It has been confirmed that it is possible to manipulate the chemical composition of whitefish by changing the composition of their diet. REFERENCES Alan¨ar¨a, A. (1992) The effect of time-restricted demand feeding on feeding activity, growth and feed conversion in rainbow trout (Oncorhynchus mykiss). Aquaculture 108, 357–368. Boujard, T. and M´edale, F. (1994) Regulation of voluntary feed intake in juvenile rainbow trout fed by hand or by self-feeders with diets containing two protein/energy ratios. Aquatic Living Resources 7, 211–215. Boujard, T., Jourdan, M., Kentouri, M. and Divanach, P. (1996) Diel feeding activity and the effect of time-restricted self-feeding on growth and feed conversion in European sea bass. Aquaculture 139, 117–127. Einen, O. and Roem, A.J. (1997) Dietary protein/energy ratios for Atlantic salmon in relation to fish size: growth, feed utilization and slaughter quality. Aquaculture Nutrition 3, 115–126. Grove, D.J., Loizides, L.G. and Nott, J. (1978) Satiation amount, frequency of feeding and gastric emptying rate in Salmo gairdneri. Journal of Fish Biology 12, 507–516. Haard, N.F. (1992) Control of chemical composition and food quality attributes of cultured fish. Food Research International 25, 289–307. Hillestad, M. and Johnsen, F. (1994) High-energy/low-protein diets for Atlantic salmon: effects on growth, nutrient retention and slaughter quality. Aquaculture 124, 109–116. J¨arvinen, A. (ed.) (1988) Proceedings of the International Symposium on Biology and Management of Coregonids. Finnish Fisheries Research 9, 1–527. Jobling, M. (1994) Fish Bioenergetics. Chapman & Hall: London, 309 pp. Jobling, M., Christiansen, J.S., Jørgensen, E.H. and Arnesen, A.M. (1993) The application of Xradiography in feeding and growth studies with fish: a summary of experiments conducted on Arctic charr. Reviews in Fisheries Science 1, 223–237. Koskela, J. (1992) Growth rates and feeding levels of European whitefish (Coregonus lavaretus) under hatchery conditions. Polskie Archiwum Hydrobiologii 39, 731–737. Koskela, J. (1995) Influence of dietary protein levels on growth and body composition of whitefish (Coregonus lavaretus). Archiv f¨ur Hydrobiologie, Advances in Limnology 46, 331–338. Leeson, S., Caston, L. and Summers, J.D. (1996a) Broiler response to energy or energy and protein dilution in the finisher diet. Poultry Science 75, 522–528.
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