7339

• UCREFRP Catalog Number: 7339
• Author: Valdez, R. A.
• Title: A Review of the Hatchery Program for Threatened and Endangered Fishes of the Colorado River.
• USFW Year: 1985.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

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3-4

3.l.3 Culture Techniques

Hatchery cul ture of the Colorado squawfi sh has establ i shed much of
the development in culture techniques for the other rare Colorado River
fishes. The first attempt to hand-strip the wild squawfish in 1973 was
largely unsuccessful. In 1974, injections with chorionic gonadotropin
produced 1 imited egg taking by hand-stripping but induced natural spawning
in gravel- lined concrete tanks (Toney 1974).

Successful
state-of-the-art
1983b):

ha tchery-producti on of Colorado squawfi sh under
techniques requires recognition of three factors

current
(Jensen

1. peak maturation of eggs masses in females,
2. proper injection of carp pituitary to stimulate ovulation of
matured eggs, and
3. appropriate water temperature for proper development.

Development of secondary sex characteristics usually occurs as water
temperature approaches 650F, usually in early May at Dexter NFH. Spawning
at Dexter NFH usually occurs in late Mayor early June as water
temperature approaches 70oF. Mal e squawfi sh develop heavy tubercul ati on
over most of their body and exhibit a golden green sheen compared to
their normal olivaceous green color. Females with maturing egg masses
exhibit soften abdomens and reddened and flowery genital papillae. All
femal es must be hand-stri pped withi n a 1 to 2-week peri od once the egg
masses ripen, or viable eggs cannot be obtained. This requires close and
careful monitorng of the females to insure procurement of viable eggs.

Female Colorado squawfish are normally injected intraperitoneally with
carp pituitary (CP) at a rate of 2 mg per pound of body weight to stimulate
ovulation of matured eggs (Hamman 1981b). Male squawfish normally stay ripe
and fluid but receive injections of human chorionic gonadotropin (HCG) at
150 IU (International Units) per pound of body weight if fluidity decreases.

The eggs of female squawfish are handstripped into pans utilizing the
wet method. Milt from two or more males is added and the eggs are stirred
gently with a feather to insure adequate mixing of sex products. Slurried
bentonite is added to the mixture to prevent the extremely adhesive eggs
from clumping. The "clayed" eggs are poured into floating egg baskets,
gently washed to remove the bentonite and allowed to water harden for 30
minutes. The eggs are then enumerated gravimetrically and placed in Heath
incubator trays or jars (Jensen 1983a, Inslee 1983). The optimum hatching
temperature for Colorado squawfish is about 700F (Marsh and Pisaro 1983).
At this temperature, hatching occurs 96 to 144 hours after fertilization
with a peak after about l20 hours. Mortality of fry can be high prior to
swimup; unattended fry have been observed to bunch together and suffocate in
groups up to 2 inches deep and 5 to 6 inches in diameter (Jensen 1983a).

Examples of fecundity (number of eggs per female) are given by Jensen
(1983b) and Inslee (1983). Fecundity of 25 domestic brood stock (Jensen
1983b) ranged from 57,766 to 133,341 eggs per female with a mean of 77,436
(mean fish weight: 3.09 lbs). A single wild female weighing 9.6 lbs
produced 242,981 eggs. The average number of eggs per pound of body weight
was 25,241 for the domestic fish and 25,310 for the wild fish.