Abstract
Estuarine fishes regularly experience fluctuations in water temperature and salinity, and many species exhibit broad tolerances that allow them to withstand extreme conditions without mortality. However, a full understanding of physiological capacities that permit occupancy of such changeable habitats also requires insight into how organismal performance responds to environmental variation. In this study, we evaluated fast-start escape performance of sheepshead minnow ( Cyprinodon variegatus ), a noted eurythermal and euryhaline estuary-resident, across temperatures near the warm extreme of its thermal range (24, 30, 36 °C) and salinities varying from low to hypersaline (2, 32, 52 ppt). Fast-start speeds were directly related to the temperature at which fish were tested, but they also exhibited dependence on acclimation conditions. Angular velocity of the initial C-bend was faster at higher test temperatures, but at any given temperature, rotation was fastest in fish held at lower temperatures and at intermediate or high salinities. While temperature and salinity effects were detectable, they were modest in magnitude. These results suggest that sheepshead minnow fast-start performance is relatively robust to environmental variability but can be influenced by fluctuating conditions within estuaries. Short-term increases in temperature brought on by daily tidal cycles may lead to elevated fast-start speeds, but long-term exposure to high temperatures (predicted to increase given climate change) or low salinities (resulting from rainwater inundation of marshes) may contribute to a reduction in fast-start performance and potentially increased vulnerability to predators.