7060

• UCREFRP Catalog Number: 7060
• Author: Berry, C. R., Jr.
• Title: Effects of Cold Shock on Colorado Squawfish Larvae
• USFW Year: 1988
• USFW - Doc Type: The Southwestern Naturalist
• Copyright Material: YES

191

The Southwestem Naturalist

vol. 33, no. 2

Tcmpcrature C01\lrol was e[[ccted diHerelllly each year. In 1981, watcr that had trickled down a
I-m degassing column emered aquaria at 70e and was heated by an aquarium heater to the
dcsired temperature. This technique probably caused supersaturation (\12%) which might have
added an additional stress (Weitkamp and Katz, 1980). However, squawfish did not show signs of
gas bubble disease (e.g., bubbles in the digestive tract or swimming or equilibrium irregularities)
before or during the experiment. Temperature comrol methods were nevertheless changed in
1985, when hot water and cold water were first mixcd to the desired temperature and then trickled
down a dc~assin~ culumn,
WaIn u'lIlperalme was decreased 5, 10, or (5oe in !i min (abrupt decrease) in half of the
aquaria and in 210 to 300 min (gradual decrease) in the remainder, except for the colllrol aquaria,
which were held at 220C. Fish were held at shock temperatures for 19 to 21 h depcnding on rate
of change and returned to 220e over 96 h at a rate of 0.05, 0.10, and 0.15oe per hour for fish
shocked with decreases of 5, 10, and 15oe, respectively. The gradual return to control
temperatures (22oe) avoided additional temperature shock. The test protocol simulated the
hypothl,tical. situation of a fish drifting from a warm river into one receiving an upstream, cold-
water discharge and then drifting downstream imo warmer waters or imo a backwater area.
Temperatures in all aquaria were routinely recorded manually, and the data was used to calibrate
recording thermographs in one aquarium for each treatment. Behavior was observed hourly
during shock and daily afterward for 21 days. Behavior of control fish was compared with that of
shocked fish. Dead fish were removed daily, Data were analyzed by categorical data analysis by the
maximum-likelihood, log-linear modeling method (Freeman, 1987).

RESULTs-Behavioral changes were minor .in fish shocked by a lOoC
abrupt decrease but ~e.-in those exposed to a ISoC abrupt drop. The
150C drop caused initial hyperactivity before the fish lost equilibrium and
floated with the current or settled to the bottom. Fish shocked by the lOoC
abrupt decrease did not lose equilibrium ~ut de<.:!.~a~d__Jh.e~t..activ.it.y. <;lnc!.,
occupied deeper portions of the water column than did control fish for
about 14 h.
-D~~ths ~..~ fish exposed to SOC and lOOG abrupt decreases occurred
randomly over the duration of the experiment rather than in the first 48 h
as observed in tanks where the temperature was lowered 150C. Therefore, I
analyzed only the cumulative mortality occurring in the first 8 days (Table
1). The ~<2:..~.<?I_d fish, ,w~r~ significantly (P = 0.001) less s-'J.~~~ptaQl~to cold
shock than _!p~~J.4-cl~y-old fish. The magnitude of shock also had a
significant (P = 0.002) effe~t 'on mortality, with the 150C decrease having the
most profound effect. However, there was also a significant (P = 0.001)
interaction between temperature and year (Table 2). The interaction
indicates that supersaturation ....Q!...Q.th.er llf~krl2\YJ1,j~ct9rs_ e!lhanc~d..rowality.,
in 1984 compared to 1985 in control, 50C shock, and lOoC shock treatments.

DISCUSSION- The present findings agree with most of the literature,
which shows that some larval fish can tolerate temperature decreases of 8 to
150C (reviewed by Coutant, 191-7.). Additionally, these data agree with
observations of the response of Colorado squawfish to cold shock made by
staff members at the Dexter National Fish Hatchery, who have cultured
squaw fish for several years (Hamman, 1981, pers, comm.). Tests on other
species have shown that the faster the rate of temperature decrease, the
greater the mortality (Speakman and Krenkel, 1972; Griffith, 1978; Burton
et aI., 1979), This relation was also evident in the comparison of Colorado
squaw[ish response to abrupt and to gradual 150C decreases in the present
study.

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