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Influence of the length of the daily feeding period on feed intake and growth of whitefish, Coregonus lavaretus
Aquaculture Aquaculture 156 (1997) 35-44
ELSEVIER
Influence of the length of the daily feeding period on feed intake and growth of whitefish, Coregonus lavaretus Juha Koskela a, Malcolm Jobling b,*, Juhani Pirhonen a a Finnish ’
Game and Fisheries Research Institute, FIN-41360
Nomegian College of Fishery
Valkola, Finland
Science, Unicersiry of Tronts@, N-9037 Trams), Norway
Accepted 22 March 1997
Abstract A study was carried out to examine the influence of the length of the daily feeding period on feed intake and growth of whitefish (initial weight 60-90 g), with the aim of providing guidelines as to the feeding regimes to be used when cultivating this species. Fish were held at 14.5”C under a 24L:OD photoperiod. Following a period during which fish were fed throughout the day, feeding regimes of 6, 12, 18 or 24 h feeding per day were imposed on 3 tanks of fish per treatment. These feeding regimes were maintained for 6 weeks during which feed intake (3 times by X-radiography) and growth were monitored. When feeding was restricted to 6 h each day daily intake tended to be initially reduced, but by the end of the experiment daily feed intake did not differ between groups of fish held on the different feeding regimes. This indicates that the fish fed according to the time-restricted regimes were able to compensate for the reduced length of the feeding period, but some weeks were required before the compensatory mechanisms took full effect. Time-restricted feeding also resulted in fish on the 6 h regime having significantly lower rates of growth (0.98 + 0.08% dd’) than those on the 24 h regime (1.42 + 0.14% dP ‘) early in the experiment. During the latter stages of the experiment, there were no significant differences in growth rates amongst the fish fed according to the different regimes. The differences established early in the trial were still apparent after 6 weeks, with overall rates of growth for the entire trial period seeming to be directly related to the length of the feeding period (6 h: 1.27 + 0.09% dP ‘; 12 h: 1.39 +0.06% dd’; 18 h: 1.46 *0.19% .d-‘; 24 h: 1.65 + 0.05% dd’). However, the only significant differences recorded were between the 6 and 24 h feeding regime groups. Length of the feeding period was not found to have any significant effect upon feed conversion, although there was a tendency for the feed:gain ratio to be lowest in the groups of fish fed according to the time-restricted feeding regimes (6 h: 0.57 + 0.05; 12 h: 0.58 + 0.06; 18 h: 0.65 + 0.07; 24 h:
* Corresponding author. Tel.: + 47 776 44000; fax: + 47 776 46020; e-mail: malcolmj @nfh.uit.no 0 1997 Elsevier Science B.V. All rights reserved. SOO44-8486(97)00079-3
0044-8486/97/$17.00 PII
.I. Koskrla et al. /Aquaculture
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156 (I 9971 35-44
0.64 f 0.08). The results indicate that whitefish are flexible in their feeding behaviour, and adapt readily to imposed regimes over a period of a few weeks. These modifications to feeding responses result in good growth performance and good feed conversion. 0 1997 Elsevier Science B.V. Krpvords:
Coregonids;
Whitefish;
Coregonus
laruretus;
Daily ration; Growth; Feeding regimes
1. Introduction Coregonids are popular food fishes in several northern and eastern European countries, and whitefish species are reared for stock enhancement purposes (Jarvinen, 1988; Todd and Luczynski, 1992; Luczynski et al., 1995). The juveniles are often reared semi-intensively, and are held in rearing ponds prior to release as one-summer fish. In recent years, attention has been directed towards intensive production methods, and it may be desirable to raise table-sized fish under intensive culture conditions. Growth and survival during the earliest life history stages of coregonids have been studied (Jarvinen, 1988; Todd and Luczynski, 1992; Luczynski et al., 19951, 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). For intensive cultivation of a fish species to be successful, there is need for knowledge about nutritional requirements, feeding practices and feed management strategies (Thorpe and Huntingford, 1992; Goddard, 1996; Jorgensen et al., 1996). Fish of several species may be able to consume sufficient food to maintain high rates of growth when fed to satiation 2-3 times per day (Andrews and Page, 1975; Grayton and Beamish, 1977; Chua and Teng, 1978; Tsevis et al., 19921, but under farming conditions it is more usual to prolong the length of the feeding period using automatic feeders that make feed available over predetermined time intervals (Alanat%, 1992; Jobling et al., 1995; Boujard et al., 1996; Goddard, 1996). Despite the fact that farmed fish may display considerable flexibility in their feeding patterns, and appear to adapt readily to artificial feeding regimes, there is evidence that the timing of feeding can influence a range of physiological and production parameters (AlanEra, 1992; Boujard and Leatherwe examined the land, 1992; Boujard et al., 1995; Jobling et al., 1995). Consequently, influence of the length of the daily feeding period on rates of feed intake and growth of whitefish, Coregonus lauaretus, to obtain information that may assist in the development of feeding practices for this species in culture.
2. Materials
and methods
The growth trial was carried out between 27 June and 09 August 1996 at the Laukaa Research Station of the Finnish Game and Fisheries Research Institute (62”30’ N, 26” E). The fish used were 1 + hatchery-reared whitefish, C. luuaretus, of the migratory Kymijoki strain. Fish for use in the experiment were derived from broodstock held at the Evo Research Station. Eggs were transported from Evo to Laukaa, and from the time of
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156 (1997) 35-44
31
hatching until the start of the experiment the fish had been held in tanks indoors and reared at ambient water temperature. On 28 May, fish for use in the experiment were selected from a larger population and individually tagged by injecting a passive integrated transponder (PIT tag, Destron/IDI) into the body cavity. One week later the experimental groups were established: twelve groups, each comprising 30 fish, were transferred to 1.7 m* hatchery tanks (volume: 0.35 m3> provided with fresh water (ca. 14S”C; range 14-15.7”C) flowing at a rate of 14 1 min-‘. Acclimatization of the fish to the experimental conditions then began. At the start of the experiment, the fish weighed 76.6 f 14.9 g (mean * sd) (Table 1). Fish were exposed to continuous light provided by lamps in the roof of the rearing hall. Four feeding regimes were established with three replicate tanks per treatment: feed supplied for 6 h per day in the period 08:00-14:00, for 12 h per day in the period 05:00-17:00, for 18 h per day between 02:OO and 20:00, and feed supplied throughout 24 h. The fish were fed on dry pellet feed (Ewes Vextra Start 3-4 mm; analysed composition-protein 55.7%, lipid 21%, energy 23.3 kJ g-‘) distributed by computercontrolled automatic feeders (Itumic) timed to release 24 portions of feed during the daily feeding session. The amounts of feed supplied to the fish were calculated by increasing the feeding rates predicted by the model presented by Koskela (1992) by 30%, and assuming a feed:gain ratio of 1.3. This ensured that feed was supplied in excess, and that the fish fed according to the different regimes were provided with similar amounts of feed. Feed intake was measured by X-radiography (Talbot and Higgins, 1983; Jobling et al., 1993) three times during the course of the experiment, with two week intervals between measurements. Diets used for feed intake measurement were prepared from sub-samples of the normal feed by grinding, homogenisation and incorporation of known quantities of X-ray dense glass beads (Ballotini: Jencons, Leighton Buzzard; sizes 7 and 9) followed by compression into pellets and re-drying at 40-45°C. Standard curves were then prepared by X-raying known weights of the marked feed and counting the numbers of ballotinis present: Ballotini Ballotini
7: 9:
Feed (g) = 0.210 + 0.015 Ballotini (n = 8; R’ = 0.964) Feed (g) = 0.045 + 0.014 Ballotini (n = 8; R2 = 0.986)
Table I Initital and final weights of whitefish, C. lamrerus,fed according to the different feeding regimes. Initital (CV,, ) and final (CV,,) size variation are also indicated, along with the coefficient of variation for growth (CV,,,) and the estimated feed/gain ratios. Values given are treatment means f sd (n = 3) Feeding regime (h) 6 Initital weight (g) CV,, Final weight (g) CV, CVSGR
Feed/gain
77.5 18.1 132.0 17.9 17.0 0.57
12 +2.1 f 1.5 54.4 +2.7 +4.2 f 0.05
79.7 19.5 140.5 17.6 13.1 0.58
18 +4.1 +2.7 i2.6 f2.0 *2.2 + 0.06
78.2 f 1.2 19.0 f 2.5 142.5 + 10.7 18.9 + 1.4 13.4 f 0.9 0.65* 0.07
24 70.9 18.6 144.4 17.5 11.5 0.64
+2.5 +2.3 +5.9 + 1.3 + 1.6 i 0.08
38
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156 (1997) 35-44
All feeds were stored at 5°C prior to use. A preliminary study was carried out to investigate the evacuation of the ballotini from the gastrointestinal tract of the fish. The results indicated that, under the conditions used in the present study, some ballotini had been passed through the gut and evacuated 9 h after the start of a feeding session. Thus, in order to avoid the underestimation of feed intake, due to evacuation of some of the ballotini, the processes involved in making feed intake measurements had to be completed within this 9 h time limit. This required a compromise to be made: all groups of fish were fed marked feed for 6 h, between 08:OO and 14:00, and the daily intakes of the fish on the longer feeding regimes were estimated by multiplication with the appropriate factor. In an attempt to check whether fish were feeding evenly throughout a feeding session, the feed intake measurements were made by providing one of the marked feeds during the first 3 h of the feeding session, and the other marked feed was supplied during the following 3 h period. This allowed recognition and separation of feed consumed by each fish during the early and late part of each feeding session. Following the termination of the feeding session with marked feeds, the fish were anaesthetised (MS-222), identified by tag-reading, 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 ballotinis present in the gastrointestinal tract of individual fish. At the end of the growth trial, the fish were returned to their rearing tanks and held on their respective feeding regimes for an additional week. At the end of this period, feed was withdrawn and the fish were then held without food for 4 days in order to evacuate the gut. The fish were then fed marked feed in excess for 3 h in an attempt to estimate the size of a ‘satiation meal’ consumed by fish that had been held on the different feeding regimes. Following completion of the feeding session, the fish were anaesthetised, X-rayed and weighed, and the amounts of feed consumed estimated from the numbers of ballotinis recorded in the gut. Growth rates (SGR) of individual fish were calculated for each rearing period according to the formula SGR = [(ln W, - In W,>/t] X 100, where W, is the weight of the fish at the start of the growth period, W, is the weight at the end of the growth period, and t is the duration of the growth period (14 d). The effects of the different treatments on interindividual variability of growth rates were assessed by comparison of coefficients of variation: CV = (sd/mean) X 100. Statistical analyses were performed using SYSTAT statistical software (SYSTAT, 19921, with possible differences among treatments and groups being tested by nested ANOVA (Sokal and Rohlf, 1995). Where appropriate, arcsine transformations of data were performed prior to the carrying out of statistical tests. In cases where significant differences among treatments were indicated, the Tukey HSD test was used for making comparisons between treatments, and P < 0.05 was taken as the level of significance.
3. Results The fish held on the 6 h feeding regime consumed significantly more food during a feeding session with marked feed than did the fish on all other regimes (Fig. IA-C).
J. Koskda
et al./Aquaculture
156 (19971 35-44
a!
16j-_ cC
,4
6
12
16
24
6
12
16
6
12
16
24
6
12
16
16
24
6
time (hours
d”)
6.
6
I 24
24
August
12 Feeding
12 Feeding
16
24
time (hours
d”)
Fig. 1, Feed intakes of whitefish, C. lararetus,fed according to the different feeding regimes (6, 12, 18 and 24 h). (A-C) Intakes during the 6 h feeding sessions with marked feed, on the three sampling dates, and (D-F) Estimated daily intakes of the fish fed for 6, 12, 18 and 24 h per day, respectively. Daily intakes were estimated by multiplying the feed intake registered during a 6 h feeding session with marked feed by the appropriate factor (2, 3 or 4) for the particular feeding regimes (12, 18 or 24 h). Data are shown as treatment means (5 sd; n = 3). Columns indicated by the same letter are not significantly different from each other.
Significant differences were found on all three days that intake was monitored. The fish held on the 6 h feeding regime also tended to consume the majority of their intake during the first 3 h of a feeding session. Significantly more than half of the daily intake was consumed during the first 3 h of the feeding session on two of the three days that intake was monitored (11 and 25 July) (Fig. 2). Feeding by the fish within the other groups was much more evenly distributed over the course of the 6 h feeding session. For the fish on the 12, 18 and 24 h feeding regimes, approximately half the intake of the marked feed was consumed during the first 3 h of the session, and about half during the second (the only significant difference from a 50:50 distribution of intake was recorded
40
J. Koskela et al./Aquaculture
123
Regime
6 h
123
12 h
156 (1997) 35-44
1
2
3
18 h
1
2
3
24 h
Fig. 2. Percentages (70 intake) of the measured feed intake consumed by whitefish, C. harem, during the first 3 of a 6 h feeding session with marked feed. Data are given for measurements made on fish held on different feeding regimes (feeding for 6, 12, 18 and 24 h per day) on 3 sampling dates (I-3). Data are shown as treatment means ( f sd; n = 3). Columns with percentages significantly different from 50% are indicated.
for the fish on the 18 h regime on 11 July) (Fig. 2). This even distribution of feeding activity between the two 3 h periods of the 6 h feeding session amongst the fish on the 12, 18 and 24 h feeding regimes suggested that the daily intake of these fish might be estimated by multiplication of measured intake by 2, 3 and 4, respectively. Estimated daily intakes of the whitefish held on the different feeding regimes are shown in Fig. ID-F. Early in the experiment, there was a general trend towards an increase in daily intake with increasing length of the daily feeding period (Fig. ID-E), but few significant differences in daily intake were recorded. On the last day of measurement, daily intakes were almost identical in all groups of fish (Fig. 1F). Feed intake during a 6 h feeding session with marked feed was always greatest amongst the fish on the 6 h feeding regime (Fig. IA-C), and by the end of the experiment the daily intakes of all groups were similar (Fig. 1F). This suggested that the fish on the 6 h feeding regime may have compensated for the reduced length of the daily feeding period by increasing their capacity to feed during the time that food was available. This could have been achieved by the fish displaying an increase in gut capacity. This possibility was tested by feeding the fish a ‘satiation meal’ following a few days of feed deprivation. The whitefish that had been held on the 6 h feeding regime consumed ‘satiation meals’ (9.6 + 0.66 g kgg ’ 3 hP ‘) that were significantly larger than those consumed by fish exposed to all other regimes (Fig. 3). Further, the fish held on the 12 h regime consumed significantly more (7.6 + 0.59 g kg-’ 3 hh’) than did the whitefish held on the 24 h feeding regime (6.0 &-0.30 g kg- ’ 3 hP ‘), whereas those on the 18 h regime took an intermediate position (6.6 + 0.31 g kg- ’ 3 hh ‘). These results suggest that the whitefish that were restricted to feeding for 6 h each day compensated for time-restricted feeding by increasing gut capacity, allowing for greater consumption during the time that feed was available. There were differences in growth between the groups of fish fed according to the different feeding regimes, and this was reflected in the final weights of the fish (treatment means & sd; n = 3: 6 h: 132.0 * 4.4 g; 12 h: 140.5 k 2.6 g; 18 h: 142.5 + 10.7 g; 24 h: 144.4 + 5.9 g> (Table 1). 0 Vera11rates of growth of the fish on the 24 h feeding
J. Koskela et nl./Aqunculture
Feeding
41
156 (19971 35-44
time (hours d“)
Fig. 3. Sizes of ‘satiation meals’ (g kg _ ’ 3 h- ‘) consumed by whitefish, C. lamretus,fed according to the different feeding time regimes (6, 12, 18 and 24 h). Fish were fed in excess for 3 h following a 4 day period of feed deprivation to empty the gut. Data are shown as treatment means (& sd; n = 3). Columns indicated by the same letter are not significantly different from each other.
regime were significantly higher than those of the fish fed for 6 h each day, but were not found to differ significantly from those of the fish in the other treatment groups (Table 2, Period l-3). More detailed analysis of the data revealed that the growth rate differences appeared early in the trial (Table 2, Period 1). There were no significant differences in rates of growth among treatments during Periods 2 and 3, even though there was an overall tendency for the fish fed for the greatest number of hours each day to grow fastest (Table 2). The growth of the fish within any given tank was quite homogeneous, although there was a tendency for growth variability (CV,,, ) to be greatest amongst the fish fed for the fewest hours each day (Table I). Thus, CVs for growth rates increased from 11.5 _t 1.6% for fish on the 24 h feeding regime to 17.0 _t 4.2% for the fish fed for 6 h each day, 13% for fish on the other two feeding regimes (12 whereas CV,,, s were approximately h regime: 13.1 &-2.2%; 18 h regime: 13.4 5 0.9%). The growth of the fish was recorded throughout the trial, and feed intake was monitored on three occasions. These data were combined to estimate the feed:gain ratios of the fish fed on the different regimes (Table 1). Treatment means (+ sd; II = 3) were found to be 0.57 f 0.05 for the fish on the 6 h feeding regime, 0.58 f 0.06 for the groups on the 12 h regime, 0.65 + 0.07 for the fish on the 18 h regime and 0.64 + 0.08
Table 2 Growth rates of whitefish, C. hnretus, fed according to different feeding three 2.week growth periods and for the entire growth trial (Period l-3) Feeding regime (h)
Period 1
6 12 18 24
0.98” l.2Yb l.35h 1.42b
Period 2 + 0.08 f 0.02 +0.12 +0.14
I .56“ 1.52” 1.55” 2.21”
regimes.
Period 3 +0.16 +0.22 f 0.59 +0.27
1.29” 1.43” I .48” 1.32”
Results are shown as treatment means f sd (n = 3). Values within columns significantly different from each other (P < 0.05).
Data are given for the Period 1-3
10.12 io.12 f0.11 kO.20
1.27” I .39”h I .46”b 1.65h
with different
f f * +
0.09 0.06 0.05 0.05
superscripts
are
42
.I. Koskela et al./Aquaculture
156 (19971 35-44
for the fish that were fed for 24 h each day. Although there was a tendency for the feed:gain ratio to increase amongst the groups fed for the greatest number of hours each day, there was not found any significant treatment effects on feed:gain ratio.
4. Discussion The fish on the 6 h feeding regime fed most avidly during the first 3 h of a feeding session, and consumed over 70% of their daily intake during this time (Fig. 2). Intense feeding early in the feeding session amongst these fish was not surprising, since 18 h had elapsed since cessation of the previous food provision. Fish held on the other feeding regimes distributed their feeding activity much more evenly over a feeding session, and this was particularly noticeable for the groups held on the 18 and 24 h feeding regimes (Fig. 2). The whitefish held on the 6 h feeding regime always consumed more during a 6 h feeding session than did conspecifics fed for longer each day (Fig. lA-C). Nevertheless, early in the experiment there was a trend towards the daily intake being directly related to the number of hours of feed provision (Fig. ID-E). By the end of the experiment, however, the daily intakes of all groups of fish were similar (Fig. 1F). These observations support the view that whitefish may readily adapt their feeding behaviour to match artificial patterns imposed by feed provision. They also indicate that the fish held on the 6 h feeding regime had been able to compensate for the reduced length of the daily feeding period by increasing their capacity to feed when food was available. Several weeks were, however, required before the compensatory mechanisms took full effect. A common response to time-restricted feeding is an increase in the size of meals brought about by an increase in gastric capacity and hypertrophy of gut tissues (Fabry, 1969). Tissue hypertrophy may commence shortly after the imposition of a time-restricted feeding regime, but some days or weeks may be required before the changes in the relative size of the gastrointestinal tract are complete. Thus, the increase in gut capacity that occurs with the passage of time may permit the daily rations of animals fed according to time-restricted regimes to increase gradually to approach those of conspecifics allowed continuous access to food. We did not measure the gut capacity of the whitefish directly, but assume that the size of the ‘satiation meal’ consumed by the fish following several days of feed deprivation reflected capacity. The fact that the whitefish that had been exposed to the 6 h feeding regime consumed significantly larger ‘satiation meals’ than fish in all other groups (Fig. 31, strongly suggests that the compensatory responses to time-restricted feeding included increased gut capacity via tissue hypertrophy. The changes in feeding patterns we observed for the whitefish on time-restricted feeding regimes are similar to those reported for European sea bass, Dicentrurchus luhrux, fed using on-demand feeders (Boujard et al., 1996). Sea bass allowed continuous access to feed had a much greater initial feed demand than did those on a time-restricted self-feeding regime, but after approximately 7 weeks the feed demand of all groups of fish was similar. By contrast, although rainbow trout, Oncorhynchus mykiss, also responded to time-restricted feeding by increasing feed demand the number of trigger
.I. Kmkela et al./Aquaculture
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actuations that led to the release of feed remained lower than that of fish allowed continuous access to feed (Alanara, 1992). However, following an initial period of a few weeks when growth rates were low amongst the time-restricted rainbow trout, growth rates increased in these groups and rates of growth were then similar under all feeding by the trout on the regimes. Further, the feed supply was used most efficiently time-restricted regime. This suggests that the feed demand by the fish given continuous access to feed was not indicative of markedly higher rates of consumption by these fish, and that the poor feed conversion shown by these trout was probably a reflection of feed wastage (Alanlra, 1992). In the study on sea bass conducted by Boujard and co-workers (Boujard et al., 1996), the growth of the fish was closely related to the total feed demand, and the lower rates of growth of the fish on the time-restricted feeding regime were attributed to the fact that the fish subjected to this regime required time to adapt to the new feeding situation. Thus, in both rainbow trout and sea bass, the initial period of reduced feed intake and growth immediately after the imposition of a time-restricted feeding regime appeared to be followed by compensatory responses that returned rates of growth to levels similar to those observed amongst fish allowed access to food for longer periods. This was also observed in our study with whitefish: daily feed intake and growth were initially depressed following the imposition of a time-restricted feeding regime (Fig. ID, Table 2, Period I), but by the end of the experiment there were no significant treatment effects upon either feed intake (Fig. 1F) or growth (Table 2, Period 3). Growth rates recorded in the present study were also similar to those reported earlier for whitefish reared at similar temperatures in intensive culture (Koskela, 1995). Growth rates of the whitefish within the groups held on the different feeding regimes were quite homogeneous, with CVs for growth being within the range lo-20% (Table I). This is a higher degree of homogeneity within groups than has usually been reported for other salmonids, in which CVs for growth rates are frequently over 25% (McCarthy et al., 1992; Jobling, 1995; Jobling et al., 1995; Jorgensen et al., 1996; Ryer and Olla, 1996). Many salmonids are territorial, especially as juveniles, whereas whitefish tend to school. Thus, the homogeneity within groups of whitefish may be a reflection of the fact that whitefish is a schooling species. Homogeneous growth, resulting in little change in size variation with time, has also been reported for sea bass, another schooling species, when fed according to time-restricted feeding regimes using demand-feeders (Boujard et al., 1996). These observations of homogeneous growth amongst schooling species imply that all fish were able to feed, even though a time-restricted feeding regime was imposed. Nevertheless, in our study with whitefish, growth appeared to be more heterogeneous amongst the fish fed for 6 h per day (CV,,, = 17.0 * 4.2%) than amongst those held on the 24 h feeding regime (CL’s,, = 11.5 k 1.6%). This increased heterogeneity amongst the whitefish held on the 6 h feeding regime is unlikely to be a reflection of increased competition for food amongst these fish, but may indicate that individual fish required different lengths of time to become adapted to the novel time-restricted feeding regime. In conclusion, the results indicate that whitefish are flexible in their feeding behaviour, and adapt readily to imposed regimes over a period of a few weeks. These modifications to feeding responses result in good growth performance and good feed
44
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conversion, but differences that arise during the adaptation period may be observed even after the fish have become adapted to the new feeding regime.
References Alan&%, 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. Andrews, J.W., Page, J.W., 1975. The effects of frequency of feeding on culture of catfish. Transactions of the American Fisheries Society 104, 317-321. Boujard, T., Leatherland, J.F., 1992. Circadian rhythms and feeding time in fishes. Environmental Biology of Fishes 35, 109-131. Boujard, T., Gelineau, A., Corraze, G., 1995. Time of a single meal influences growth performance in rainbow trout, Oncorhynchus mykiss (Walbaum). Aquaculture Research 26, 34 l-349. Boujard, T., Jourdan, M., Kentouri, M., Divanach, P., 1996. Die1 feeding activity and the effect of time-restricted self-feeding on growth and feed conversion in European sea bass. Aquaculture 139, 117-127. Chua, T.-E., Teng, S.-K., 1978. Effects of feeding frequency on the growth of young estuary grouper, Epinephelus tawina (Forskall, cultured in floating net cages. Aquaculture 14, 31-47. Fabry, P.. 1969. Feeding Pattern and Nutritional Adaptations. Butterworths, London. Goddard, S., 1996. Feed Management in Intensive Aquaculture. Chapman and Hall, London. Grayton, B.D., Beamish, F.W.H., 1977. Effects of feeding frequency on food intake, growth and body composition of rainbow trout (Salmo gairdneri). Aquaculture 1 I. 159- 172. Jobling, M., 1995. Feeding of charr in relation to aquaculture. Nordic Journal of Freshwater Research 71, 102-I 12. Jobling, M., Arnesen, A.M., Baardvik, B.M., Christiansen, J.S., Jorgensen, E.H., 1995. Monitoring feeding behaviour and food intake: Methods and applications. Aquaculture Nutrition I, 13 I- 143. Jobling, M., Christiansen, J.S., Jorgensen, E.H., Arnesen, A.M., 1993. The application of X-radiography in feeding and growth studies with fish: A summary of experiments conducted on Arctic charr. Reviews in Fisheries Science 1, 223-237. Jiirvinen, A. (Ed.). 1988. Proceedings of the International Symposium on Biology and Management of Coregonids. Finnish Fisheries Research 9, l-527. Jorgensen, E.H., Baardvik, B.M., Eliassen, R., Jobling, M., 1996. Food acquisition and growth of juvenile Atlantic salmon (Salmo solar) in relation to spatial distribution of food. Aquaculture 143, 277-289. Koskela. J., 1992. Growth rates and feeding levels of European whitefish (CoreRonus Iac,aretus) under hatchery conditions. Polskie Archiwum Hydrobiologii 39, 73 l-737. Koskela, J., 1995. Influence of dietary protein levels on growth and body composition of whitefish (Coregonus lacaretus). Archiv fur Hydrobiologie, Advances in Limnology 46, 33 l-338. Luczynski, M., Bodaly, R.A., Bond, W.A., Eckman, R., Kamler, E.. Mills, K.H., Reist, J.D., RGsch, R., Segner, H., Todd, T.N. (Eds.1, 1995. Biology and Management of Coregonid Fishes-1993. Archiv fiir Hydrobiologie, Advances in Limnology 46, l-485. McCarthy, I.D., Carter, C.G., Houlihan, D.F., 1992. The effect of feeding hierarchy on individual variability in daily feeding of rainbow trout, Oncorh~nchus mykiss (Walbaum). Journal of Fish Biology 41, 257-263. Ryer, C.H., Olla, B.L., 1996. Growth depensation and aggression in laboratory reared coho salmon: The effect of food distribution and ration size. Journal of Fish Biology 48, 686-694. Sokal, R.R., Rohlf, F.J., 1995. Biometry. Freeman, New York. SYSTAT, 1992. SYSTAT for Windows: Statistics Version 5. SYSTAT Inc., Evanston, Talbot, C., Higgins, P.J., 1983. A radiographic method for feeding studies on fish using metallic iron powder as a marker. Journal of Fish Biology 23, 2 1 I-220. Thorpe, J.E., Huntingford, F.A. (Eds.1, 1992. The Importance of Feeding Behavior for the Efficient Culture of Salmonid Fishes. World Aquaculture Society, Baton Rouge. Todd, T.N., Luczynski. M., 1992. Biology and Management of Coregonid Fishes- 1990. Polskie Archiwum Hydrobiologii 39, 247-894. Tsevis, N., Klaoudatos, S., Conides, A., 1992. Food conversion budget in sea bass, Dicentrarchu.s labrax, fingerlings under two different feeding frequency patterns. Aquaculture 101, 292-304.
ELSEVIER
Influence of the length of the daily feeding period on feed intake and growth of whitefish, Coregonus lavaretus Juha Koskela a, Malcolm Jobling b,*, Juhani Pirhonen a a Finnish ’
Game and Fisheries Research Institute, FIN-41360
Nomegian College of Fishery
Valkola, Finland
Science, Unicersiry of Tronts@, N-9037 Trams), Norway
Accepted 22 March 1997
Abstract A study was carried out to examine the influence of the length of the daily feeding period on feed intake and growth of whitefish (initial weight 60-90 g), with the aim of providing guidelines as to the feeding regimes to be used when cultivating this species. Fish were held at 14.5”C under a 24L:OD photoperiod. Following a period during which fish were fed throughout the day, feeding regimes of 6, 12, 18 or 24 h feeding per day were imposed on 3 tanks of fish per treatment. These feeding regimes were maintained for 6 weeks during which feed intake (3 times by X-radiography) and growth were monitored. When feeding was restricted to 6 h each day daily intake tended to be initially reduced, but by the end of the experiment daily feed intake did not differ between groups of fish held on the different feeding regimes. This indicates that the fish fed according to the time-restricted regimes were able to compensate for the reduced length of the feeding period, but some weeks were required before the compensatory mechanisms took full effect. Time-restricted feeding also resulted in fish on the 6 h regime having significantly lower rates of growth (0.98 + 0.08% dd’) than those on the 24 h regime (1.42 + 0.14% dP ‘) early in the experiment. During the latter stages of the experiment, there were no significant differences in growth rates amongst the fish fed according to the different regimes. The differences established early in the trial were still apparent after 6 weeks, with overall rates of growth for the entire trial period seeming to be directly related to the length of the feeding period (6 h: 1.27 + 0.09% dP ‘; 12 h: 1.39 +0.06% dd’; 18 h: 1.46 *0.19% .d-‘; 24 h: 1.65 + 0.05% dd’). However, the only significant differences recorded were between the 6 and 24 h feeding regime groups. Length of the feeding period was not found to have any significant effect upon feed conversion, although there was a tendency for the feed:gain ratio to be lowest in the groups of fish fed according to the time-restricted feeding regimes (6 h: 0.57 + 0.05; 12 h: 0.58 + 0.06; 18 h: 0.65 + 0.07; 24 h:
* Corresponding author. Tel.: + 47 776 44000; fax: + 47 776 46020; e-mail: malcolmj @nfh.uit.no 0 1997 Elsevier Science B.V. All rights reserved. SOO44-8486(97)00079-3
0044-8486/97/$17.00 PII
.I. Koskrla et al. /Aquaculture
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0.64 f 0.08). The results indicate that whitefish are flexible in their feeding behaviour, and adapt readily to imposed regimes over a period of a few weeks. These modifications to feeding responses result in good growth performance and good feed conversion. 0 1997 Elsevier Science B.V. Krpvords:
Coregonids;
Whitefish;
Coregonus
laruretus;
Daily ration; Growth; Feeding regimes
1. Introduction Coregonids are popular food fishes in several northern and eastern European countries, and whitefish species are reared for stock enhancement purposes (Jarvinen, 1988; Todd and Luczynski, 1992; Luczynski et al., 1995). The juveniles are often reared semi-intensively, and are held in rearing ponds prior to release as one-summer fish. In recent years, attention has been directed towards intensive production methods, and it may be desirable to raise table-sized fish under intensive culture conditions. Growth and survival during the earliest life history stages of coregonids have been studied (Jarvinen, 1988; Todd and Luczynski, 1992; Luczynski et al., 19951, 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). For intensive cultivation of a fish species to be successful, there is need for knowledge about nutritional requirements, feeding practices and feed management strategies (Thorpe and Huntingford, 1992; Goddard, 1996; Jorgensen et al., 1996). Fish of several species may be able to consume sufficient food to maintain high rates of growth when fed to satiation 2-3 times per day (Andrews and Page, 1975; Grayton and Beamish, 1977; Chua and Teng, 1978; Tsevis et al., 19921, but under farming conditions it is more usual to prolong the length of the feeding period using automatic feeders that make feed available over predetermined time intervals (Alanat%, 1992; Jobling et al., 1995; Boujard et al., 1996; Goddard, 1996). Despite the fact that farmed fish may display considerable flexibility in their feeding patterns, and appear to adapt readily to artificial feeding regimes, there is evidence that the timing of feeding can influence a range of physiological and production parameters (AlanEra, 1992; Boujard and Leatherwe examined the land, 1992; Boujard et al., 1995; Jobling et al., 1995). Consequently, influence of the length of the daily feeding period on rates of feed intake and growth of whitefish, Coregonus lauaretus, to obtain information that may assist in the development of feeding practices for this species in culture.
2. Materials
and methods
The growth trial was carried out between 27 June and 09 August 1996 at the Laukaa Research Station of the Finnish Game and Fisheries Research Institute (62”30’ N, 26” E). The fish used were 1 + hatchery-reared whitefish, C. luuaretus, of the migratory Kymijoki strain. Fish for use in the experiment were derived from broodstock held at the Evo Research Station. Eggs were transported from Evo to Laukaa, and from the time of
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31
hatching until the start of the experiment the fish had been held in tanks indoors and reared at ambient water temperature. On 28 May, fish for use in the experiment were selected from a larger population and individually tagged by injecting a passive integrated transponder (PIT tag, Destron/IDI) into the body cavity. One week later the experimental groups were established: twelve groups, each comprising 30 fish, were transferred to 1.7 m* hatchery tanks (volume: 0.35 m3> provided with fresh water (ca. 14S”C; range 14-15.7”C) flowing at a rate of 14 1 min-‘. Acclimatization of the fish to the experimental conditions then began. At the start of the experiment, the fish weighed 76.6 f 14.9 g (mean * sd) (Table 1). Fish were exposed to continuous light provided by lamps in the roof of the rearing hall. Four feeding regimes were established with three replicate tanks per treatment: feed supplied for 6 h per day in the period 08:00-14:00, for 12 h per day in the period 05:00-17:00, for 18 h per day between 02:OO and 20:00, and feed supplied throughout 24 h. The fish were fed on dry pellet feed (Ewes Vextra Start 3-4 mm; analysed composition-protein 55.7%, lipid 21%, energy 23.3 kJ g-‘) distributed by computercontrolled automatic feeders (Itumic) timed to release 24 portions of feed during the daily feeding session. The amounts of feed supplied to the fish were calculated by increasing the feeding rates predicted by the model presented by Koskela (1992) by 30%, and assuming a feed:gain ratio of 1.3. This ensured that feed was supplied in excess, and that the fish fed according to the different regimes were provided with similar amounts of feed. Feed intake was measured by X-radiography (Talbot and Higgins, 1983; Jobling et al., 1993) three times during the course of the experiment, with two week intervals between measurements. Diets used for feed intake measurement were prepared from sub-samples of the normal feed by grinding, homogenisation and incorporation of known quantities of X-ray dense glass beads (Ballotini: Jencons, Leighton Buzzard; sizes 7 and 9) followed by compression into pellets and re-drying at 40-45°C. Standard curves were then prepared by X-raying known weights of the marked feed and counting the numbers of ballotinis present: Ballotini Ballotini
7: 9:
Feed (g) = 0.210 + 0.015 Ballotini (n = 8; R’ = 0.964) Feed (g) = 0.045 + 0.014 Ballotini (n = 8; R2 = 0.986)
Table I Initital and final weights of whitefish, C. lamrerus,fed according to the different feeding regimes. Initital (CV,, ) and final (CV,,) size variation are also indicated, along with the coefficient of variation for growth (CV,,,) and the estimated feed/gain ratios. Values given are treatment means f sd (n = 3) Feeding regime (h) 6 Initital weight (g) CV,, Final weight (g) CV, CVSGR
Feed/gain
77.5 18.1 132.0 17.9 17.0 0.57
12 +2.1 f 1.5 54.4 +2.7 +4.2 f 0.05
79.7 19.5 140.5 17.6 13.1 0.58
18 +4.1 +2.7 i2.6 f2.0 *2.2 + 0.06
78.2 f 1.2 19.0 f 2.5 142.5 + 10.7 18.9 + 1.4 13.4 f 0.9 0.65* 0.07
24 70.9 18.6 144.4 17.5 11.5 0.64
+2.5 +2.3 +5.9 + 1.3 + 1.6 i 0.08
38
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All feeds were stored at 5°C prior to use. A preliminary study was carried out to investigate the evacuation of the ballotini from the gastrointestinal tract of the fish. The results indicated that, under the conditions used in the present study, some ballotini had been passed through the gut and evacuated 9 h after the start of a feeding session. Thus, in order to avoid the underestimation of feed intake, due to evacuation of some of the ballotini, the processes involved in making feed intake measurements had to be completed within this 9 h time limit. This required a compromise to be made: all groups of fish were fed marked feed for 6 h, between 08:OO and 14:00, and the daily intakes of the fish on the longer feeding regimes were estimated by multiplication with the appropriate factor. In an attempt to check whether fish were feeding evenly throughout a feeding session, the feed intake measurements were made by providing one of the marked feeds during the first 3 h of the feeding session, and the other marked feed was supplied during the following 3 h period. This allowed recognition and separation of feed consumed by each fish during the early and late part of each feeding session. Following the termination of the feeding session with marked feeds, the fish were anaesthetised (MS-222), identified by tag-reading, 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 ballotinis present in the gastrointestinal tract of individual fish. At the end of the growth trial, the fish were returned to their rearing tanks and held on their respective feeding regimes for an additional week. At the end of this period, feed was withdrawn and the fish were then held without food for 4 days in order to evacuate the gut. The fish were then fed marked feed in excess for 3 h in an attempt to estimate the size of a ‘satiation meal’ consumed by fish that had been held on the different feeding regimes. Following completion of the feeding session, the fish were anaesthetised, X-rayed and weighed, and the amounts of feed consumed estimated from the numbers of ballotinis recorded in the gut. Growth rates (SGR) of individual fish were calculated for each rearing period according to the formula SGR = [(ln W, - In W,>/t] X 100, where W, is the weight of the fish at the start of the growth period, W, is the weight at the end of the growth period, and t is the duration of the growth period (14 d). The effects of the different treatments on interindividual variability of growth rates were assessed by comparison of coefficients of variation: CV = (sd/mean) X 100. Statistical analyses were performed using SYSTAT statistical software (SYSTAT, 19921, with possible differences among treatments and groups being tested by nested ANOVA (Sokal and Rohlf, 1995). Where appropriate, arcsine transformations of data were performed prior to the carrying out of statistical tests. In cases where significant differences among treatments were indicated, the Tukey HSD test was used for making comparisons between treatments, and P < 0.05 was taken as the level of significance.
3. Results The fish held on the 6 h feeding regime consumed significantly more food during a feeding session with marked feed than did the fish on all other regimes (Fig. IA-C).
J. Koskda
et al./Aquaculture
156 (19971 35-44
a!
16j-_ cC
,4
6
12
16
24
6
12
16
6
12
16
24
6
12
16
16
24
6
time (hours
d”)
6.
6
I 24
24
August
12 Feeding
12 Feeding
16
24
time (hours
d”)
Fig. 1, Feed intakes of whitefish, C. lararetus,fed according to the different feeding regimes (6, 12, 18 and 24 h). (A-C) Intakes during the 6 h feeding sessions with marked feed, on the three sampling dates, and (D-F) Estimated daily intakes of the fish fed for 6, 12, 18 and 24 h per day, respectively. Daily intakes were estimated by multiplying the feed intake registered during a 6 h feeding session with marked feed by the appropriate factor (2, 3 or 4) for the particular feeding regimes (12, 18 or 24 h). Data are shown as treatment means (5 sd; n = 3). Columns indicated by the same letter are not significantly different from each other.
Significant differences were found on all three days that intake was monitored. The fish held on the 6 h feeding regime also tended to consume the majority of their intake during the first 3 h of a feeding session. Significantly more than half of the daily intake was consumed during the first 3 h of the feeding session on two of the three days that intake was monitored (11 and 25 July) (Fig. 2). Feeding by the fish within the other groups was much more evenly distributed over the course of the 6 h feeding session. For the fish on the 12, 18 and 24 h feeding regimes, approximately half the intake of the marked feed was consumed during the first 3 h of the session, and about half during the second (the only significant difference from a 50:50 distribution of intake was recorded
40
J. Koskela et al./Aquaculture
123
Regime
6 h
123
12 h
156 (1997) 35-44
1
2
3
18 h
1
2
3
24 h
Fig. 2. Percentages (70 intake) of the measured feed intake consumed by whitefish, C. harem, during the first 3 of a 6 h feeding session with marked feed. Data are given for measurements made on fish held on different feeding regimes (feeding for 6, 12, 18 and 24 h per day) on 3 sampling dates (I-3). Data are shown as treatment means ( f sd; n = 3). Columns with percentages significantly different from 50% are indicated.
for the fish on the 18 h regime on 11 July) (Fig. 2). This even distribution of feeding activity between the two 3 h periods of the 6 h feeding session amongst the fish on the 12, 18 and 24 h feeding regimes suggested that the daily intake of these fish might be estimated by multiplication of measured intake by 2, 3 and 4, respectively. Estimated daily intakes of the whitefish held on the different feeding regimes are shown in Fig. ID-F. Early in the experiment, there was a general trend towards an increase in daily intake with increasing length of the daily feeding period (Fig. ID-E), but few significant differences in daily intake were recorded. On the last day of measurement, daily intakes were almost identical in all groups of fish (Fig. 1F). Feed intake during a 6 h feeding session with marked feed was always greatest amongst the fish on the 6 h feeding regime (Fig. IA-C), and by the end of the experiment the daily intakes of all groups were similar (Fig. 1F). This suggested that the fish on the 6 h feeding regime may have compensated for the reduced length of the daily feeding period by increasing their capacity to feed during the time that food was available. This could have been achieved by the fish displaying an increase in gut capacity. This possibility was tested by feeding the fish a ‘satiation meal’ following a few days of feed deprivation. The whitefish that had been held on the 6 h feeding regime consumed ‘satiation meals’ (9.6 + 0.66 g kgg ’ 3 hP ‘) that were significantly larger than those consumed by fish exposed to all other regimes (Fig. 3). Further, the fish held on the 12 h regime consumed significantly more (7.6 + 0.59 g kg-’ 3 hh’) than did the whitefish held on the 24 h feeding regime (6.0 &-0.30 g kg- ’ 3 hP ‘), whereas those on the 18 h regime took an intermediate position (6.6 + 0.31 g kg- ’ 3 hh ‘). These results suggest that the whitefish that were restricted to feeding for 6 h each day compensated for time-restricted feeding by increasing gut capacity, allowing for greater consumption during the time that feed was available. There were differences in growth between the groups of fish fed according to the different feeding regimes, and this was reflected in the final weights of the fish (treatment means & sd; n = 3: 6 h: 132.0 * 4.4 g; 12 h: 140.5 k 2.6 g; 18 h: 142.5 + 10.7 g; 24 h: 144.4 + 5.9 g> (Table 1). 0 Vera11rates of growth of the fish on the 24 h feeding
J. Koskela et nl./Aqunculture
Feeding
41
156 (19971 35-44
time (hours d“)
Fig. 3. Sizes of ‘satiation meals’ (g kg _ ’ 3 h- ‘) consumed by whitefish, C. lamretus,fed according to the different feeding time regimes (6, 12, 18 and 24 h). Fish were fed in excess for 3 h following a 4 day period of feed deprivation to empty the gut. Data are shown as treatment means (& sd; n = 3). Columns indicated by the same letter are not significantly different from each other.
regime were significantly higher than those of the fish fed for 6 h each day, but were not found to differ significantly from those of the fish in the other treatment groups (Table 2, Period l-3). More detailed analysis of the data revealed that the growth rate differences appeared early in the trial (Table 2, Period 1). There were no significant differences in rates of growth among treatments during Periods 2 and 3, even though there was an overall tendency for the fish fed for the greatest number of hours each day to grow fastest (Table 2). The growth of the fish within any given tank was quite homogeneous, although there was a tendency for growth variability (CV,,, ) to be greatest amongst the fish fed for the fewest hours each day (Table I). Thus, CVs for growth rates increased from 11.5 _t 1.6% for fish on the 24 h feeding regime to 17.0 _t 4.2% for the fish fed for 6 h each day, 13% for fish on the other two feeding regimes (12 whereas CV,,, s were approximately h regime: 13.1 &-2.2%; 18 h regime: 13.4 5 0.9%). The growth of the fish was recorded throughout the trial, and feed intake was monitored on three occasions. These data were combined to estimate the feed:gain ratios of the fish fed on the different regimes (Table 1). Treatment means (+ sd; II = 3) were found to be 0.57 f 0.05 for the fish on the 6 h feeding regime, 0.58 f 0.06 for the groups on the 12 h regime, 0.65 + 0.07 for the fish on the 18 h regime and 0.64 + 0.08
Table 2 Growth rates of whitefish, C. hnretus, fed according to different feeding three 2.week growth periods and for the entire growth trial (Period l-3) Feeding regime (h)
Period 1
6 12 18 24
0.98” l.2Yb l.35h 1.42b
Period 2 + 0.08 f 0.02 +0.12 +0.14
I .56“ 1.52” 1.55” 2.21”
regimes.
Period 3 +0.16 +0.22 f 0.59 +0.27
1.29” 1.43” I .48” 1.32”
Results are shown as treatment means f sd (n = 3). Values within columns significantly different from each other (P < 0.05).
Data are given for the Period 1-3
10.12 io.12 f0.11 kO.20
1.27” I .39”h I .46”b 1.65h
with different
f f * +
0.09 0.06 0.05 0.05
superscripts
are
42
.I. Koskela et al./Aquaculture
156 (19971 35-44
for the fish that were fed for 24 h each day. Although there was a tendency for the feed:gain ratio to increase amongst the groups fed for the greatest number of hours each day, there was not found any significant treatment effects on feed:gain ratio.
4. Discussion The fish on the 6 h feeding regime fed most avidly during the first 3 h of a feeding session, and consumed over 70% of their daily intake during this time (Fig. 2). Intense feeding early in the feeding session amongst these fish was not surprising, since 18 h had elapsed since cessation of the previous food provision. Fish held on the other feeding regimes distributed their feeding activity much more evenly over a feeding session, and this was particularly noticeable for the groups held on the 18 and 24 h feeding regimes (Fig. 2). The whitefish held on the 6 h feeding regime always consumed more during a 6 h feeding session than did conspecifics fed for longer each day (Fig. lA-C). Nevertheless, early in the experiment there was a trend towards the daily intake being directly related to the number of hours of feed provision (Fig. ID-E). By the end of the experiment, however, the daily intakes of all groups of fish were similar (Fig. 1F). These observations support the view that whitefish may readily adapt their feeding behaviour to match artificial patterns imposed by feed provision. They also indicate that the fish held on the 6 h feeding regime had been able to compensate for the reduced length of the daily feeding period by increasing their capacity to feed when food was available. Several weeks were, however, required before the compensatory mechanisms took full effect. A common response to time-restricted feeding is an increase in the size of meals brought about by an increase in gastric capacity and hypertrophy of gut tissues (Fabry, 1969). Tissue hypertrophy may commence shortly after the imposition of a time-restricted feeding regime, but some days or weeks may be required before the changes in the relative size of the gastrointestinal tract are complete. Thus, the increase in gut capacity that occurs with the passage of time may permit the daily rations of animals fed according to time-restricted regimes to increase gradually to approach those of conspecifics allowed continuous access to food. We did not measure the gut capacity of the whitefish directly, but assume that the size of the ‘satiation meal’ consumed by the fish following several days of feed deprivation reflected capacity. The fact that the whitefish that had been exposed to the 6 h feeding regime consumed significantly larger ‘satiation meals’ than fish in all other groups (Fig. 31, strongly suggests that the compensatory responses to time-restricted feeding included increased gut capacity via tissue hypertrophy. The changes in feeding patterns we observed for the whitefish on time-restricted feeding regimes are similar to those reported for European sea bass, Dicentrurchus luhrux, fed using on-demand feeders (Boujard et al., 1996). Sea bass allowed continuous access to feed had a much greater initial feed demand than did those on a time-restricted self-feeding regime, but after approximately 7 weeks the feed demand of all groups of fish was similar. By contrast, although rainbow trout, Oncorhynchus mykiss, also responded to time-restricted feeding by increasing feed demand the number of trigger
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actuations that led to the release of feed remained lower than that of fish allowed continuous access to feed (Alanara, 1992). However, following an initial period of a few weeks when growth rates were low amongst the time-restricted rainbow trout, growth rates increased in these groups and rates of growth were then similar under all feeding by the trout on the regimes. Further, the feed supply was used most efficiently time-restricted regime. This suggests that the feed demand by the fish given continuous access to feed was not indicative of markedly higher rates of consumption by these fish, and that the poor feed conversion shown by these trout was probably a reflection of feed wastage (Alanlra, 1992). In the study on sea bass conducted by Boujard and co-workers (Boujard et al., 1996), the growth of the fish was closely related to the total feed demand, and the lower rates of growth of the fish on the time-restricted feeding regime were attributed to the fact that the fish subjected to this regime required time to adapt to the new feeding situation. Thus, in both rainbow trout and sea bass, the initial period of reduced feed intake and growth immediately after the imposition of a time-restricted feeding regime appeared to be followed by compensatory responses that returned rates of growth to levels similar to those observed amongst fish allowed access to food for longer periods. This was also observed in our study with whitefish: daily feed intake and growth were initially depressed following the imposition of a time-restricted feeding regime (Fig. ID, Table 2, Period I), but by the end of the experiment there were no significant treatment effects upon either feed intake (Fig. 1F) or growth (Table 2, Period 3). Growth rates recorded in the present study were also similar to those reported earlier for whitefish reared at similar temperatures in intensive culture (Koskela, 1995). Growth rates of the whitefish within the groups held on the different feeding regimes were quite homogeneous, with CVs for growth being within the range lo-20% (Table I). This is a higher degree of homogeneity within groups than has usually been reported for other salmonids, in which CVs for growth rates are frequently over 25% (McCarthy et al., 1992; Jobling, 1995; Jobling et al., 1995; Jorgensen et al., 1996; Ryer and Olla, 1996). Many salmonids are territorial, especially as juveniles, whereas whitefish tend to school. Thus, the homogeneity within groups of whitefish may be a reflection of the fact that whitefish is a schooling species. Homogeneous growth, resulting in little change in size variation with time, has also been reported for sea bass, another schooling species, when fed according to time-restricted feeding regimes using demand-feeders (Boujard et al., 1996). These observations of homogeneous growth amongst schooling species imply that all fish were able to feed, even though a time-restricted feeding regime was imposed. Nevertheless, in our study with whitefish, growth appeared to be more heterogeneous amongst the fish fed for 6 h per day (CV,,, = 17.0 * 4.2%) than amongst those held on the 24 h feeding regime (CL’s,, = 11.5 k 1.6%). This increased heterogeneity amongst the whitefish held on the 6 h feeding regime is unlikely to be a reflection of increased competition for food amongst these fish, but may indicate that individual fish required different lengths of time to become adapted to the novel time-restricted feeding regime. In conclusion, the results indicate that whitefish are flexible in their feeding behaviour, and adapt readily to imposed regimes over a period of a few weeks. These modifications to feeding responses result in good growth performance and good feed
44
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conversion, but differences that arise during the adaptation period may be observed even after the fish have become adapted to the new feeding regime.
References Alan&%, 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. Andrews, J.W., Page, J.W., 1975. The effects of frequency of feeding on culture of catfish. Transactions of the American Fisheries Society 104, 317-321. Boujard, T., Leatherland, J.F., 1992. Circadian rhythms and feeding time in fishes. Environmental Biology of Fishes 35, 109-131. Boujard, T., Gelineau, A., Corraze, G., 1995. Time of a single meal influences growth performance in rainbow trout, Oncorhynchus mykiss (Walbaum). Aquaculture Research 26, 34 l-349. Boujard, T., Jourdan, M., Kentouri, M., Divanach, P., 1996. Die1 feeding activity and the effect of time-restricted self-feeding on growth and feed conversion in European sea bass. Aquaculture 139, 117-127. Chua, T.-E., Teng, S.-K., 1978. Effects of feeding frequency on the growth of young estuary grouper, Epinephelus tawina (Forskall, cultured in floating net cages. Aquaculture 14, 31-47. Fabry, P.. 1969. Feeding Pattern and Nutritional Adaptations. Butterworths, London. Goddard, S., 1996. Feed Management in Intensive Aquaculture. Chapman and Hall, London. Grayton, B.D., Beamish, F.W.H., 1977. Effects of feeding frequency on food intake, growth and body composition of rainbow trout (Salmo gairdneri). Aquaculture 1 I. 159- 172. Jobling, M., 1995. Feeding of charr in relation to aquaculture. Nordic Journal of Freshwater Research 71, 102-I 12. Jobling, M., Arnesen, A.M., Baardvik, B.M., Christiansen, J.S., Jorgensen, E.H., 1995. Monitoring feeding behaviour and food intake: Methods and applications. Aquaculture Nutrition I, 13 I- 143. Jobling, M., Christiansen, J.S., Jorgensen, E.H., Arnesen, A.M., 1993. The application of X-radiography in feeding and growth studies with fish: A summary of experiments conducted on Arctic charr. Reviews in Fisheries Science 1, 223-237. Jiirvinen, A. (Ed.). 1988. Proceedings of the International Symposium on Biology and Management of Coregonids. Finnish Fisheries Research 9, l-527. Jorgensen, E.H., Baardvik, B.M., Eliassen, R., Jobling, M., 1996. Food acquisition and growth of juvenile Atlantic salmon (Salmo solar) in relation to spatial distribution of food. Aquaculture 143, 277-289. Koskela. J., 1992. Growth rates and feeding levels of European whitefish (CoreRonus Iac,aretus) under hatchery conditions. Polskie Archiwum Hydrobiologii 39, 73 l-737. Koskela, J., 1995. Influence of dietary protein levels on growth and body composition of whitefish (Coregonus lacaretus). Archiv fur Hydrobiologie, Advances in Limnology 46, 33 l-338. Luczynski, M., Bodaly, R.A., Bond, W.A., Eckman, R., Kamler, E.. Mills, K.H., Reist, J.D., RGsch, R., Segner, H., Todd, T.N. (Eds.1, 1995. Biology and Management of Coregonid Fishes-1993. Archiv fiir Hydrobiologie, Advances in Limnology 46, l-485. McCarthy, I.D., Carter, C.G., Houlihan, D.F., 1992. The effect of feeding hierarchy on individual variability in daily feeding of rainbow trout, Oncorh~nchus mykiss (Walbaum). Journal of Fish Biology 41, 257-263. Ryer, C.H., Olla, B.L., 1996. Growth depensation and aggression in laboratory reared coho salmon: The effect of food distribution and ration size. Journal of Fish Biology 48, 686-694. Sokal, R.R., Rohlf, F.J., 1995. Biometry. Freeman, New York. SYSTAT, 1992. SYSTAT for Windows: Statistics Version 5. SYSTAT Inc., Evanston, Talbot, C., Higgins, P.J., 1983. A radiographic method for feeding studies on fish using metallic iron powder as a marker. Journal of Fish Biology 23, 2 1 I-220. Thorpe, J.E., Huntingford, F.A. (Eds.1, 1992. The Importance of Feeding Behavior for the Efficient Culture of Salmonid Fishes. World Aquaculture Society, Baton Rouge. Todd, T.N., Luczynski. M., 1992. Biology and Management of Coregonid Fishes- 1990. Polskie Archiwum Hydrobiologii 39, 247-894. Tsevis, N., Klaoudatos, S., Conides, A., 1992. Food conversion budget in sea bass, Dicentrarchu.s labrax, fingerlings under two different feeding frequency patterns. Aquaculture 101, 292-304.