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

as red shiner, and one (about 8 mm TL) was identified as fathead minnow. Interestingly,

the smallest Colorado squawfish had four prey fish (all red shiner), whereas only one or two

fish were found in digestive tracts of the others. Gut contents for six Colorado squawfish

36-48 mm TL and the 73 mm TL specimen were exclusively fish; those for the remaining

specimens were 70-80% fish. Digestive tracts of six Colorado squawfish contained 2-6

cestode parasites (species undetermined, but probably Proteocephalus

ptvchocheilus-Flagg 1982); cestodes were not found in guts of other fishes. Colorado

squawfish infested with cestodes were larger than 27 mm TL and were collected from both

river reaches in fall.

Diet Overlap

Degree of diet overlap between yay Colorado squawfish and other fishes among

subsets was influenced mainly by proportions of zooplankton and especially immature

dipterans consumed (Table 2). Within each reach, diet overlap for all length intervals of

Colorado squawfish generally decreased as length of other species increased. Degree of

diet overlap among fish of similar size was generally greater in the lower than upper reach.

Overlap values were < 0.60 (range = 0.10-0.59) for most comparisons; generally, values

were lowest for comparisons with fathead minnow and bluehead sucker. Biologically

important overlap (values> 0.60) occurred only between Colorado squawfish > 10 mm TL

and some comparisons with native speckled dace and flannelmouth sucker and nonnative

red shiner, green sunfish, and especially channel catfish. These higher overlap values were

primarily attributed to the high relative importance of immature midges in diets and,

secondarily, especially for the comparison with green sunfish greater> 40 mm TL (upper

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