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

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Density. The density of fish in pounds that can be reared in a cubic
foot of rearing space is estimated by dividing the total length of the
fish in inches by 2. For example, 1 pound of 2-inch fish can be
reared in a cubic foot of water. Similarly, two pounds of 4-inch fish
can be reared in the same volume of rearing space.
Fifty thousand (50,000) razorback suckers could be reared in the
hatchery building to the end of the first growing season in 100
troughs (i' wide X 1.5' deep X 4' long; described in Section VII.B.3.)
and a total water flow of 190 gallons per minute. These fish would be
fed commercial dry feed and should be provided supplemental feeding in
zooplankton every two or three days. One or two outdoor ponds would
be required to raise the zooplankton.
Growth. The average growth as an increase in total length for a unit
of time (e.g., month) is constant for a group of fish at a given
temperature until the fish reach sexual maturity. For example, the
average growth of razorback sucker is 0.75 inches per month until the
fish reach maturity at a water temperature of 70 F (21 C).
Temperature. For practical purposes, the growth of all four of the
endangered Colorado River fishes ceases when the water temperature is
below 50 F (10 C) and is directly proportional with increasing water
temperatures. Yearling Colorado squawfish preferred a water
temperature of 77 F (25 C) (Black and Bulkley 1985a) and exhibited the
fastest growth at that temperature (Black and Bulkley 1985b).
Hatchery water temperatures are seldom constant and a system of
temperature units has been developed based on the fact that an
increase in length is linearly related to water temperature. Since
the endangered Colorado River fishes cease to grow at water
temperatures below 50 F (10 C), the temperature units (T.U.) would be
equal to the average water temperature minus 50 F times the time in
months. However, the growth rate in length as related to water
temperature has not been empirically determined for the endangered
Colorado River fishes.
Feeding Rate. Feeding rate can be calculated in percent of body
weight per day based on expected growth at a given water temperature
and adjusted at five-day intervals. The food required is calculated
by multiplying the percentage of body weight per day by the weight of
the fish in pounds. The following formula can be used to determine
the percentage of body weight per day:
Percent of body weight per day = 30-day growth in inches 1/ X
food conversion factor X 10 divided by the length of the fish in
inches.
For example, the percent of body weight per day for 2-inch fish
reared at 70 F (21 C) at a food conversion factor of 1.5 would
be:
0.75 X 1.5 X 10 = 11.25 = 5.6 percent of body weight per day
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