1. We constructed a cost-effective environmental chamber by modifying a dual heating–cooling microbiological incubator.
2. In round gobies, Apollonia melanostoma, critical thermal maximum temperature (onset of spasms, OS) was significantly higher than the mean loss of righting response (LRR) temperature. Neither temperature endpoint was correlated to body mass or total body length.
3. Opercular ventilation rates (OVR) were positively correlated to ambient temperature change. Q10 values for OVR were 1.26 (Δ16→26 °C) to 1.23 (Δ20→30 °C).
4. With respect to thermal tolerance, the round goby is unlikely a factor in recruitment failure of the mottled sculpin, Cottus bairdi.