Poststocking Harvest of Catchable‐Sized Rainbow Trout Enhanced by Dietary Supplementation with a Fully Fermented Commercial Yeast Culture during Hatchery Rearing

Abstract

AbstractCatchable‐sized salmonids are often stocked without regard to their hatchery rearing history, including the diets used. To evaluate the possible effects of a proprietary, fully fermented yeast Saccharomyces cerevisiae dietary supplement (DVAqua; Diamond V Mills, Cedar Rapids, Iowa) on poststocking harvest, Shasta‐strain rainbow trout Oncorhynchus mykiss (280 mm) were fed either a hatchery diet containing 0.125% yeast product or a control diet prior to four stockings over the course of 3 months in two small put‐and‐take fishing lakes (Upper Mirror and Lower Mirror lakes, South Dakota). An angler census indicated that for each lake on each of four stocking dates, rainbow trout receiving yeast supplementation were harvested at higher rates than fish fed the control diet; each lake had one stocking for which the percent harvest of fish fed the yeast‐supplemented diet was more than 30% higher than that of control fish. Overall, returns to the creel in Upper Mirror and Lower Mirror lakes were 17% and 13% higher, respectively, for fish fed the yeast‐supplemented diet than for control fish. Most of the rainbow trout were harvested within 2 weeks after stocking, with no difference in timing of harvest observed between the two diet groups. In addition to experiencing greater harvest by anglers during the census, more fish fed the yeast‐supplemented diet were recovered from each lake after the census through a combination of gillnetting and voluntary tag reporting by fishermen. The results suggest that rainbow trout fed the yeast‐supplemented diet during hatchery rearing consistently returned to the creel in significantly greater numbers than fish receiving the control diet. Fisheries managers may want to consider these results when requesting hatchery‐produced catchable rainbow trout for put‐and‐take waters.