9488

• UCREFRP Catalog Number: 9488
• Author: Mueller, G. A., J. Carpenter, P. C. Marsh and C. O. Minckley.
• Title: Cibola High Levee Pond Annual Report 2003.
• USFW Year: 2003.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

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Bullfrog Tadpole~Fish Egg Test. During routine field sampling, several adult razorbacks
freely expressed gametes in the holding tan1e Four hUndred of these eggs were salvaged
for predation experiments with bullfrog tadpoles obtained from CHLP.

Four 10-gal aquarium tanks were filled with 7 gal of water and aerated. One hundred
razorback eggs were placed in each tank. Twenty-five tadpoles were placed in each of
three tanks, leaving one as a control (no tadpoles). Lengths of 10 tadpoles were
measured in each group (Table 3). Water temperatures ranged from 20 to 220C. The
experiment started Thursday afternoon and ended Monday morning, approximately 90
hours later. We were unable to make daily observations.

Crayfish-Razorback Fry. Tests were conducted examining crayfish predation on
razorback sucker fry. Three sets oftests were conducted using four lO-gal tanks. The
experiments were designed to determine if razorback sucker fry utilized overhead cover
and to examine associated predation rates.

Table 3. Bullfrog tadpoles used in egg predation experiments.

Bullfrog tadpoles

Tank 1

Tank 2

Tank 3

Tank 4

Wet weight (g)
Length range (mm.)
Average length (mm)

102
54-83
75

108
48-89
75

104
46-82
73

Control

Each tank: was elevated (10 cm) on one end using a block of wood and filled with 7 gal of
water. This provided both a shallow (10 cm) and deep (20 cm) end. Plastic, imitation
hydrilla was used in two experiments to determine if fry werc attracted to the cover
regardless of water depth. On one test the cover was placed near the surface of the
shallow end and in the second test it was placed in the deep end.

Razorback sucker fry were counted and measured and 20 were placed into each
aquarium. Two crayfish were then placed in each of three tanks. Fry were fed brine
shrimp (Artemia) once a day and their numbers were counted after 24,48, and 72 hours.

Potential Predators of Razorback Larvae. To examine potential predation by multiple
predator species, eight 30-gal tanks were set up at Achii Hanyo and Willow Beach
hatcheries. Predators were obtained from Willow Beach, captured within the lower
Colorado River basin, or acquired from aquaculturists (Table 4). The fish farms gave us

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