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
groups. Interindividual variabilities in feed intake were generally greater in the
groups of charr exposed to static water (CVG: 63 and 120%) and to a current speed
of 0.5 body lengths per second (CVG: 45 and 80%) than in those subjected to more
rapid water flows of 1.0, 1.5, and 2.0 body lengths per second (CVG: 59 and 76%;
69 and 57%; 65 and 42%); in the unexercised groups, CVs and SGRs were
significantly negatively correlated (Spearman rank test: R = -0.492* [n = 201; -0.769'**
[n = 19]). Thus, the analyses provide evidence that strong feeding hierarchies
developed in the groups of charr held in static water, with the levels of social
interactions within these groups probably being an important contributory factor to
the poor rates of weight gain displayed by these fish. The observation that
salmonids, including charr, exposed to flowing water tend to display increased
schooling behavior and decreased numbers of agonistic encounters compared to
conspecifics reared in standing water (East and Magnan, 1987; Christiansen et al.,
1989, 1991, 1992; Christiansen and Jobling, 1990) lends support to the contention
that exposure to water currents has a marked influence on social behavior, and this
may, in turn, also affect rates of feed acquisition and growth performance.
The energetic costs of agonistic behavior are not known with any degree of
certainty, but the performance of such behavior has been shown to give rise to
marked, but transient, increases in rates of oxygen consumption (Brett, 1964, 1973;
Brett and Sutherland, 1965; Umezawa et al., 1983). The performance of sustained
swimming is, however, known to be metabolically expensive, and when fish have
been forced to swim against water currents in tunnel respirometers, rates of energy
expenditure have often been found to increase exponentially with increasing
swimming speed (Beamish, 1978; Brett and Groves, 1979). Measurements of rates
of oxygen consumption carried out on Arctic charr suggest that metabolic expen-
diture may be similar for groups of fish forced to swim at moderate speeds against
water currents and those performing routine swimming activity (Christiansen et al.,
1991). Inasmuch as the routine activities of fish held in groups include agonistic
behavior, it seems probable that the metabolic costs associated with the performance
of such behavior may be relatively high.
In addition to behavioral changes, forcing the fish to perform sustained exercise
also may bring about changes in body composition, lead to changes in the structure
of the swimming muscles, and induce changes in rates of protein synthesis, turnover,
and deposition (Houlihan and Laurent, 1987; Christiansen et al., 1989; Davison,
1989). All of these physiological changes induced by sustained swimming activity at
moderate speeds probably contribute to the observed increase in growth rates and
improved feed efficiency ratios seen in exercised fish.
Vlll. CONCLUDING COMMENTS
X-radiography can be used to obtain valuable information about a number of aspects
of digestive physiology and gastrointestinal function (Talbot, 1985; Grove, 1986; dos
Santos and Jobling, 1991). If attempts are made to use the method described by
Talbot and Higgins (1983), problems may arise in studies where the main aim is the
estimation of gastric evacuation rates due to the differential emptying of the X-ray
dense marker and nutrient components of the meal.
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