8123

• UCREFRP Catalog Number: 8123
• Author: Wydoski, R. S.
• Title: Coordinated Hatchery Facility Plan
• USFW Year: 1994.
• USFW - Doc Type: Need for Captive-Reared Endangered Fish and Propagation Facilities.
• Copyright Material: NO

judgement of experienced fish culturists was used to select data that
described growth that could be expected for the razorback sucker,
bonytail, humpback chub, and Colorado squawfish at the end of each growing ,
season under hatchery conditions in the Upper Colorado River Basin.
The standard for growth at the end of each growing season until the fish
reach sexual maturity is provided for razorback sucker, bonytail, humpback
chub, and Colorado squawfish in Tables 4, 5, 6, and 7, respectively.
Nearly all bonytail and humpback chubs mature when they reach 14 inches in
total length; razorback suckers and Colorado squawfish mature when they
are 16 inches or longer in total length.
The average water temperature during the growing season in the upper basin
was assumed to be approximately 70 F (21 Q. The growing season for the
first year was less than for successive years to adjust for the spawning
season. For practical purposes, growth of the endangered Colorado River
fishes ceases when water temperatures are below 50 F (10C). It was
assumed that the fish would grow at a constant rate until they reached
sexual maturity. The average growth per month was calculated from
empirical data.
Attrition (i.e., mortality) rates were estimated by concensus by members
of the Propagation Subcommittee and Biology Committee. Attrition rates
between fertilized egg stage and the end of the first growing season can
be highly variable. Sufficient fertilized eggs should be obtained from
wild fish so that 500 progeny remain at the end of the first growing
season from each family lot. The attrition rate between the end of the '
first growing season and the second was considered to be 50%; 2nd and
3rd - 20%; 3rd and 4th - 20%; and beyond the 4th - 5% annually. To ensure
adequate numbers of both sexes to serve as broodstock in a primary refuge
and a back-up refuge (30 fish each composed of 15 males and 15 females),
it was concluded that 500 fish should be retained per family lot at the
end of the first growing season. That number of fish should be sufficient
to provide 60 adults of equal sexes at maturity. Based on these attrition
rates, the expected number of fish remaining at the end of each growing
season would be: 1 - 500 fish; 2 - 250 fish; 3 - 200 fish; 4 - 160 fish; 5
- 152 fish, and 6 - 144 fish. These numbers could change when better
estimates of attrition rates become available and culture techniques are
perfected for these species.
Condition factors that appear to apply to the endangered Colorado River ,
fishes were 4.5 for the razorback sucker, 4.0 for the humpback chub, and
3.0 for the bonytail and Colorado squawfish. The condition factor (C) was
calculated by dividing the weight (W) of a fish in pounds by the ,
cube of its total length (L) in inches (English system; C = W times 10'
divided by L').
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(1982) using the average total length and the condition factor. The total
weight of each family lot cohort was calculated by dividing the number of
fish per pound into the number remaining at the end of each growing
season. The average weight of family lot cohorts of razorback
sucker, bonytail, humpback chub, and Colorado squawfish are provided in
Tables 4, 5, 6 and 7 respectively. Average weight of family lot cohorts ,
44 '