7771

• UCREFRP Catalog Number: 7771
• Author: Muth, R. T. and D. E. Snyder.
• Title: Diets of Young Colorado Squawfish and Other Small Fish in Backwaters of the Green River, Colorado and Utah.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

lesser extent, red shiner and channel catfish < 31 mm TL and flannelmouth sucker.
Cladocerans (many identified as Daphina, Eurvcercus. and Macrothrix) and especially
cyclopoid copepods (many identified as Cvclops) represented most of the zooplankton
found in digestive tracts. Identified genera of rotifers included Brachionus. Cephalodella.
Keratella, Lecane, Monostvla. Polvarthra, and Trichocerca. Proportional contribution of
zooplankton to diets of all fishes tended to decrease as fish length increased.
Bluehead sucker was the only species to eat moderate amounts of algae (10-30% of
food volume); other fishes consumed minor amounts of algae. Algae consisted mostly of
six diatom genera (Cvmbella, Fraoilaria. Gvrosioma, Navicula. Surirella, and Svnedra), one
desmid genus (Closterium), and, to a lesser extent, Pediastrum (a colonial green alga).
Most digestive tracts contained debris, and it accounted for a moderate or large proportion
of gut contents (> 30%) in all fishes except speckled dace and green sunfish. Debris
consisted of fibrous particles of vascular plant tissue usually mixed with large amounts of
clay particles and sand grains, suggesting direct feeding on the bottom. It was a
predominant component of gut contents for flannelmouth sucker and particularly fathead
minnow and bluehead sucker. Plant seeds were eaten by all fishes, but especially by red
shiner < 31 mm TL; many plant seeds found in digestive tracts were identified as tamarisk
Tamarix oallica, an introduced exotic.
Two observations were unique to Colorado squawfish. Fish larvae were found in
digestive tracts of 10 Colorado squawfish (about 1 % of total examined); one was 21 mm TL,
eight were 36-48 mm TL, and one was 73 mm TL (probably a yearling). No fish were
detected in digestive tracts of the other species. Of the 18 fish larvae found, most were too
digested for species identification or accurate length measurement, but all were cypriniforms
(mostly cyprinids) and probably ~ 10 mm TL. Six fish larvae (6-9 mm TL) were identified

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