Using Temperature and Salinity Tolerances to Predict the Success of the Shimofuri Goby, a Recent Invader into California

Shimofuri gobies Tridentiger bifasciatus recently invaded the San Francisco Estuary of California and appear to be physiologically well suited to the region. To assess the range expansion capability of the shimofuri goby, I used standard techniques to measure the critical thermal maxima (CTMax) at eight combinations of temperature (10°C and 20°C) and salinity (0, 5, 10, and 20‰) and I measured chronic upper salinity tolerance (CUST) at 20°C. Shimofuri goby CTMax was 37°C when acclimated to 20°C and was 31–34°C when acclimated to 10°C. These values surpass those of most other resident fishes and allow the gobies to survive in small isolated pools at low tide, where temperatures change quickly and often exceed 30°C. Shimofuri goby CUST was 17‰, typical for estuarine fishes, but insufficient to allow for range expansion through seawater. Shimofuri gobies have been transported via the California State Water Project into freshwater reservoirs, where they appear to have established reproducing populations. From these populations, they may disperse downstream into southern Californian estuaries, possibly threatening the federally endangered tidewater goby Eucyclogobius newberryi.