Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Wildland Resources

Department name when degree awarded

Fisheries and Wildlife

Committee Chair(s)

Todd A. Crowl


Todd A. Crowl


Wayne Wurtsbaugh


David Beauchamp


Dana Vaughan


The effects of different daily temperature regimes and food availability on growth rates of Colorado squawfish (Ptychocheilus lucius) were determined using field and laboratory experiments. Daily temperature and food gradients were observed in river backwaters (important nursery habitat for juvenile Colorado squawfish). High fluctuating temperatures (± 5-8° C) were observed daily in the shallow, terminal ends of backwaters. Where backwaters were in contact with the river (mouth), daily temperature fluctuations decreased (± 2° C). Food availability also varied spatially between the mouth and end of each backwater. To test whether Colorado squawfish growth rates varied in different areas of backwaters along these gradients, a series of cage experiments was performed. Cages were placed in each backwater at the end (high temperature fluctuation), middle (moderate temperature fluctuation), and mouth (low temperature fluctuation). Colorado squawfish growth rates were significantly higher near the mouth of the backwater where temperatures were more constant.

In laboratory aquaria, Colorado squawfish growth rates were observed at three different temperature regimes, similar to those found in backwaters (±0°, ±3°, and ±7° C). As with field experiments, growth rates were high in the low fluctuating temperature treatment; however, they were not significantly different from the highly fluctuating temperature treatment. Behavioral observations of Colorado squawfish movement performed using a large (5 m x 1 m x 0.5 m) Plexiglas tank with a temperature regime similar to that found in backwaters suggested that Colorado squawfish spent the majority of their time in the deeper part of the tank where the least amount of temperature fluctuation occurred.