Effect of temperature on growth at ration and gastric evacuation rate of ruffe

We investigated the effect of temperature on gastric evacuation rate and growth at ration of ruffe Gymnocephalus cernuus because of its importance for estimating food consumption by this invasive nuisance species. Gastric evacuation rate was estimated at 8, 14, 19, and 23°C using groups of 16–48 fish that were fed chironomid larvae, an important prey species for many ruffe populations. Growth at ration was estimated at 14, 19, and 23°C for daily rations of 2, 4, and 8% of body mass using groups of 7–8 fish. Gastric evacuation rate (R) was related to temperature (T) by the exponential function R = 0.024 × e^{0.075 × T}; r ² = 0.90. Between 8°C and 23°C, the magnitude of the temperature response of R was less for ruffe than for yellow perch Perca flavescens and European perch P. fluviatilis, but the European perch and ruffe R versus temperature functions intersected at approximately 4°C. Growth of ruffe ranged from −0.24 to 0.55% of wet body mass per day, increased with ration, and declined with increasing temperature. Our results suggest that, compared with perch, ruffe are better adapted to cooler temperatures and that their metabolism is less sensitive to temperature.