Performance and behavior of cutthroat trout ( Oncorhynchus clarki) reared in covered raceways or demand fed

Abstract

Cutthroat trout ( Oncorhynchus clarki Utah) were reared in outdoor raceways with or without plywood covers. The same hand-fed controls for this experiment were also used to test the effects of demand feeding. Growth, feed conversion, and mortality did not differ ( P > 0.05) among the hand-fed covered, hand-fed uncovered (control), and demand-fed groups after 256 days. Autopsy-based parameters were generally not significantly different among groups. However, hematocrit and the fat index were significantly higher in covered raceways after 166 days. The fin index was significantly lower in covered raceways on both Day 166 and 225. Pectoral fin erosion was significantly reduced in covered raceways relative to controls by Day 166, but did not differ by Day 225. Demand feeding did not improve fin condition. Observations of cover preference were made for four fish groups over a 45 min period, either in the presence of a stuffed eagle or without it. All groups significantly preferred cover, but there were no differences related to rearing under cover or the presence of a predator model. Covers did improve fin condition and fat levels of fish during early rearing, but the benefits were not sustained throughout the rearing period. Use of demand feeders did not produce tangible health or growth benefits, but did not negatively impact the fish either. Demand feeding reduced the labor required to feed the fish, but increased cleaning time.