Temperature preferences of hardhead Mylopharodon conocephalus and rainbow trout Oncorhynchus mykiss in an annular chamber

Abstract

To optimize habitat characteristics when managing resident and migratory stream fish populations in regulated systems, it is important to know a species’ preferred temperatures. However, temperature-preference devices used in many laboratory studies often have design limitations (e.g., confounding variables such as differential light intensities or water depths, or perceived cover) limiting their usefulness. To overcome these design limitations, we constructed a 3-m-diameter, annular preference apparatus made of clear, acrylic plastic capable of presenting uniform light intensities, constant water depths and velocities, and stable vertical and horizontal temperature gradients for experimental fish. We determined preferred temperatures of hardhead Mylopharodon conocephalus (mean TL: 36.2 cm) and rainbow trout Oncorhynchus mykiss (mean TL: 35.4 cm) acclimated to 12, 15, and 18 °C and tested, individually, in the 12–24 °C annular gradient. All hardhead acclimation groups avoided waters <17 °C, whereas trout acclimated to 12 and 15 °C consistently avoided water >19 °C, and 18 °C acclimated trout avoided water temperatures <16 °C and >20 °C. Including all acclimation temperature groups, mean hardhead preferred water temperatures ranged from 19.6 °C to 21.0 °C (mean modal preferences were 20.2–21.5 °C), whereas trout preferred significantly cooler average water temperatures ranging from 16.0 °C to 18.4 °C (mean modal preferences were 15.8–18.5 °C). These temperature preference data can be used to guide regulation of stream systems for key fish species.