Temperature, dissolved oxygen, and salinity tolerances of five prairie stream fishes and their role in explaining fish assemblage patterns

We compared the maximum temperature, maximum salinity, and minimum dissolved oxygen tolerances of two cyprinodontids and three cyprinids to identify the abiotic factors that determine assemblage structure in drying streambed pools. Red River pupfish Cyprinodon rubrofluviatilis, plains killifish Fundulus zebrinus, plains minnow Hybognathus placitus, smalleye shiner Notropis buccula, and sharpnose shiner N. oxyrhynchus all have high thermal, low dissolved oxygen, and high salinity tolerances. Cyprinodontids were able to tolerate temperatures between 39°C and 42°C, salinities up to 40‰, and dissolved oxygen concentrations as low as 0.95 mg/L, whereas cyprinids were tolerant of temperatures between 37°C and 41°C, salinities up to 14‰, and dissolved oxygen concentrations as low as 2.1 mg/L. Our laboratory results provide compelling evidence that the greater salinity tolerances of cyprinodontids can explain temporal changes in fish assemblages in evaporating streambed pools and may in part explain the spatial zonation of species within the upper Brazos River Basin, Texas.