University of California Water Resources Center

This project was designed to determine the temperature requirements of native California stream fishes. The importance of temperature in regulating the abundance and distribution of fishes has been well-documented, although primarily for species from the eastern United States and Canada. Three sets of experiments were used to define the thermal niches of these fishes - acute temperature preferences, routine metabolic rates, and critical thermal maxima. Acclimation temperature preferenda for hardhead (Mylopharodon conocephalus), Sacramento squawfish (Ptychocheilus grandis), hitch (Lavinia exilicauda), and California roach (Lavinia symmetricus) were 28.35, 26.04, 30.67, and 24.72 [degrees]C, respectively. Partial data for Sacramento blackfish (Orthodon microlepidotus), Sacramento perch (Archoplites interruptus), tule perch (Hysterocarpus traski), and Sacramento sucker (Catostomus occidentalis) are also presented. Plots of standard deviations of preferred temperatures at each acclimation temperature provided an estimate of the relative activity of each species, both intraspecifically and interspecifically. Routine metabolic rates were highest and most variable for squawfish, and most gradual (with increasing temperatures) for hardhead. Critical thermal maxima (CTM) generally increased with increasing acclimation temperatures for each species. All the values were quite close (within 4 [degrees]C at heach test temperature), randing from 28.29 [degrees]C for squawfish at 10 [degrees]C to 38.14 [degrees]C for hitch at 30 [degrees]C.

The laboratory results generally agree with field observations of macrohabitats of the species tested. For example, California roach had the lowest of the four preferenda, and are found at slightly higher elevations where the temperatures can be cooler than for the other species. Squawfish showed generally high activity levels in the temperature preference trough and high metabolic rates, corresponding to their roving and piscivorous feeding habits. High preferenda and low metabolic rates were determined for hitch, corresponding to their occurrences in lower elevation, warmer waters with little or no velocity.

This project is important to provide background information for management agencies. Other studies have shown that preferred temperatures are optimal for growth, which also implies feeding and, indirectly, for reproduction as well. Man-made alterations) such as diversion dams, channelization, or removal of riparian vegetation can change stream thermal regimes that reduce the efficiencies of these fish set activities, or in extreme cases, threaten their survival. Along with temperature changes from these alterations are usually changes in oxygen levels of the water, which may become stressful to the resident species. The critical thermal maxima can be used to detect sublethal doses of pollutants or the presence of disease before mortalities occur.

Management personnel can sample stream sites for fish species and water temperatures, and then with the background information provided in this report, can predict the impact of proposed water projects or determine the effects of existing ones. Recommendations can then be made for modifications in plans or existing structures so that the impacts on native fish populations and communities can be minimized.