9334

• UCREFRP Catalog Number: 9334
• Author: Stickney, R. R.
• Title: Editor
• USFW Year: Series
• USFW - Doc Type: 1993
• Copyright Material: YES

JOBLING ET AL. REVIEWS IN FISHERIES SCIENCE
V. D/EL FEEDING PATTERNS
In addition to having application in the estimation of daily feed intake, the
X-radiographic method allows investigation of diel changes in feeding behavior. Diel
feeding patterns of Arctic charr have been examined at different seasons of the year
for fish taken from the wild (J~rgensen and Jobling, 1989), and for those reared in
a hatchery environment throughout their lives. Marked seasonal variations were
recorded in the times of day during which fish fed most actively (Figure 2), but
patterns of feed intake were similar for the wild-caught and hatchery-reared charr.
At certain times of the year, the charr consumed a large proportion of their daily feed
intake at night, and there were usually peaks of feeding activity around dusk and
dawn. The overall diel and seasonal changes in feeding patterns of Arctic charr
appear to be similar to those of rainbow trout (Oncorhynchus mykiss) (Landless,
1976), but differ markedly from those of Atlantic salmon, which appear to feed
predominantly during daylight hours, irrespective of season (Higgins and Talbot,
1985; Jorgensen and Jobling, 1992).
Although the X-radiographic technique can be used to study diel changes in
patterns of feed intake (Higgins and Talbot, 1985; Jorgensen and Jobling, 1989,
1992), information about feeding activity is collected more easily and cheaply using
on-demand feeding systems (Landless, 1976; Alanara, 1992a,b; Boujard et ai., 1992).
On-demand feeding systems may be constructed to possibly allow monitoring each
release of feed as a discrete event under conditions where feed is continuously
available to the fish. Thus, these systems enable long-term automatic recording of
data without disturbance to the fish.
Vl. MODES OF FEEDING BEHAVIOR
The fact that Arctic charr often consumed much of their daily feed intake at night
Qorgensen and Jobling, 1989) led to the hypothesis that foraging on the bottom may
be an important feeding mode for the species. The hypothesis was tested by
comparing the daily feed intakes of groups of fish prevented from reaching feed
lying on the tank bottom with intakes of fish allowed free access to the bottom.
Irrespective of the lighting conditions used in the tests, the feed intake of charr
allowed access to feed lying on the tank bottom was significantly greater than intake
of charr forced to forage in the water column (Jorgensen and Jobling, 1990). When
a similar study was carried out on Atlantic salmon (Jorgensen and Jobling, 1992), the
results were different from those obtained in the charr experiments. Atlantic salmon
appear to be far less dependent on bottom foraging in order to obtain adequate
amounts of feed (Figure 3).
The results presented above refer to short-term experiments, and further con-
firmation of the importance of bottom feeding for charr was obtained in longer-term
growth experiments conducted over a period of 17 weeks. On each of the four
occasions on which daily feed intake was estimated, fish allowed access to feed lying
on the bottom had consumed significantly more than the fish forced to forage in the
water column. These differences in feed intake affected growth. The Arctic charr
given free access to the feed lying on the tank bottom almost doubled their body
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