INFLUENCE OF THE LENGTH OF THE DAILY FEEDING PERIOD ON FEED-INTAKE AND GROWTH OF WHITEFISH, COREGONUS-LAVARETUS

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 w eight 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 1 4.5 degrees C under a 24L:OD photoperiod. Following a period during wh ich 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. Th ese feeding regimes were maintained for 6 weeks during which feed inta ke (3 times by X-radiography) and growth were monitored. When feeding was restricted to 6 h each day daily intake tended to be initially red uced, but by the end of the experiment daily feed intake did not diffe r between groups of fish held on the different feeding regimes. This i ndicates that the fish fed according to the time-restricted regimes we re able to compensate for the reduced length of the feeding period, bu t some weeks were required before the compensatory mechanisms took ful l effect. Time-restricted feeding also resulted in fish on the 6 h reg ime having significantly lower rates of growth (0.98 +/- 0.08% d(-1)) than those on the 24 h regime (1.47 +/- 0.14% d(-1)) early in the expe riment. During the latter stages of the experiment, there were no sign ificant 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 th e entire trial period seeming to be directly related to the length of the feeding period (6 h: 1.27 +/- 0.09% d(-1); 12 h: 1.39 +/- 0.06% d( -1); 18 h: 1.46 +/- 0.19% . d(-1); 24 h: 1.65 +/- 0.05% d(-1)). Howeve r, the only significant differences recorded were between the 6 and 24 h feeding regime groups. Length of the feeding period was not found t o 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: 0.64 +/- 0.08). T he results indicate that whitefish are flexible in their feeding behav iour, and adapt readily to imposed regimes over a period of a few week s. These modifications to feeding responses result in good growth perf ormance and good feed conversion. (C) 1997 Elsevier Science B.V.