7760

• UCREFRP Catalog Number: 7760
• Author: Beyers, D. W., R. T. Muth and M. S. Farmer.
• Title: Experimental Evidence of Competition Between Larvae of Colorado Squawfish and Fathead Minnow.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

abundance without facilitating or inhibiting feeding due to super-abundance or
scarcity of food.
The number of zooplankton introduced into aquaria was not adjusted to
account for mortality of fish because small size and rapid deterioration of
dead fish made accurate counting difficult. Zooplankton abundance within
aquaria was not measured. Inspection of aquaria showed that living
zooplankton did not accumulate in any of the experimental treatments.
The experiment was concluded 1 h after the second feeding on day 14.
Surviving fish were removed from aquaria, sacrificed by administering an
overdose of anesthesia (tricaine methanesulfonate, Argent Chemical
Laboratories, Redmond, Washington), and preserved in 10 % formalin. Preserved
fish were sorted by species, counted, blotted, and their wet mass was
determined (± 1 mg).
Five Colorado squawfish and five fathead minnow were randomly selected
from each replicate for diet analysis. Guts (from esophagus to vent) were
removed by dissection. No evidence of regurgitation of gut contents was
observed. Gut contents were examined under magnification, and individual food
items were identified and enumerated by categories: cladocera, copepods,
rotifers, or nauplii.
Statistical analysis
The response of relative growth (r), where r = (w2 - w~)/w~ and w~ and w2
are mass at beginning and end of the experiment, was used to infer effects of
competition. Survivorship was measured, but the experiment duration was too
short to permit its use for study of competitive effects because non-feeding
fish could have remained alive via internal energy reserves. Data were
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