Potential for Resource Competition between Eurasian Ruffe and Yellow Perch: Growth and RNA Responses in Laboratory Experiments

Abstract

The ruffe Gymnocephalus cernuus, an exotic percid from Eurasia that is now established in limited areas of the Great Lakes, is invading areas currently occupied by native yellow perch Perca flavescens. We conducted two laboratory experiments to determine whether competition for benthic macroinvertebrate food (live aquatic oligochaetes) may occur, thereby resulting in reduced growth for one or both fish species. In the first experiment, we compared the short-term (7-d) growth of ruffe and yellow perch among four treatments: one individual (ruffe or yellow perch), two conspecifics (two ruffe or two yellow perch), one fish of each species together, and two fish of each species together (N = 9 per treatment). Growth was measured both as change in mass and as RNA levels in the white muscle tissue of fish, which is an index of short-term growth. In the second experiment, we looked at longer-term (58-d) growth using three treatments: two conspecifics alone, one fish of each species together, and two fish of each species together (N = 3 per treatment). The growth rates of ruffe did not differ significantly from those of yellow perch in a given treatment in either experiment. In both experiments, however, the growth of both species declined about 70% in the high-density treatments (two fish of each species together) compared with the low-density treatments. The results of RNA analyses were consistent with change in mass and represent an alternative approach to assessing growth responses. In ruffe−yellow perch interactions in nature, total fish density may be more important than species composition in determining growth rates when food is limiting. Therefore, ruffe invasions that increase overall fish density may be detrimental to the growth of yellow perch.