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
Although problems may be experienced by those trying to use the method for
the collection of data required for the determination of rates of gastric evacuation,
the method has proven to be suitable for use in studies of feeding behavior (Higgins
and Talbot, 1985; Talbot, 1985; Jorgensen and Jobling, 1989, 1990). The method also
may find application in studies where quantitative information about feed intake of
either individuals or groups of fish is required (Talbot, 1985; Jobling et al., 1989;
Jorgensen and Jobling, 1990; Thorpe et al., 1990).
This paper provides a summary of results obtained in experiments using the
quantitative X-radiographic method, and applications of the method to the study of
various aspects of feed intake, feeding behavior, and feed-growth relationships of
Arctic chary are described.
ll. X-RADIOGRAPHY APPLIED TO FISH FEEDING
STUDIES
The X-radiographic method was described in detail by Talbot and Higgins (1983)
and only a brief general description is given here. Prior to a feed intake measure-
ment, fish are continuously supplied with feed distributed using automatic disc
feeders. At the start of the measurement period, the "normal" feed is replaced by
feed of the same nutritional composition, but formulated to contain a low concen-
tration of particulate X-ray dense marker. The type (electrolytic iron powder or glass
"Ballotini" spheres), size, and concentration of the marker incorporated into the feed
are varied depending on the size of the fish and on the length of time over which
feed intake is to be monitored. On completion of a measurement period, fish are
anesthetized using benzocaine (100 ppm) and X-ray photographed. Following
development of the X-ray plates, the number of marker particles present in the
gastrointestinal tract of the fish is counted, thereby allowing an estimate of the
amount of feed consumed to be made.
X-radiography has been used in the estimation of feed intake of Arctic chary held
under a variety of rearing conditions. Full details of holding conditions and
experimental methodology have been presented by Jorgensen and Jobling (1989,
1990) and Palsson et al. (1992).
The method also has been used to study changes in feed intake of chary following
abrupt transfer from freshwater to waters with salinities ranging from 10 to 35 ppt.
(Amesen et a1., 1993). Fourteen groups (n = 40 fish per group) of immature Arctic chary
(20 to 24 cm fork length) were established and held in freshwater at 8°C for a period
of 4 weeks. At the start of the experiment, on Ol April, salinity of the water in each
tank was rapidly changed to the desired salinity (0, 10, 15, 20, 25, 30, or 35 ppt) by
adjusting the proportions of fresh- and seawater flowing into the tank. This gave two
replicate tanks of fish for each of seven salinity treatments. Feed intake was estimated
on two occasions, 3 and 30 days after the fish had been exposed to the abrupt changes
in salinity. Commercial feed (3-mm pellets; FK Start) containing X-ray dense marker
(0.49 to 0.70 mm "Ballotini" spheres at an inclusion level of 0.7% by weight) was
provided to the fish for 24 h. Fish were then anesthetized, weighed, and X-ray
photographed. Records were made of the proportions of feeding fish within each
treatment group, and the feed intake of each individual also was estimated.
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