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

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Berry-Cold Shock EHects on Ptychocheilus lucius Larvae

195

TAB!.E I-Number of dead 14- and 40-day-old squawfish 8 days after being subjected to abrupt,
A (5 min), and gradual, G (240 to 300 min) temperature decreases of 5, 10, and I !IDe.

Fish ant" Time Number 01 Temperalure denea.. (oG)
(days, Yt'ar illlt"rY~11 lish' (~mlrol 5 10 15
14 1984 A 200 27 21 22 76
G 200 34 24 34 48
1985 A 150 I 0 2 83
G 150 I 3 0 16
40 1984 A 200 6 2 4 I
G 200 3 2 3 !I
'III 19M.1, lish w,',e held ill twu a4ua,ia; ill 19M5. ill llm't' a4uaria.

The effects of age also seem important since the 40-day-old fish were
unaffected by temperature decreases. The young of other species are usually
more sensitive than adults (Pitkow, 1960; Nickum, 1966; Elliott, 1981),
probably because the change in body temperature is more rapid in smaller
fish. Body weight was not recorded in this study, but the small difference in
body weight between 14. and 40-day-old squawfish probably had little effect
on the rate of body temperature change. Resistance to cold shock in the 40-
day-old fish was more likely due to their advanced development and ability
to tolerate physiological effects of cold shock (Houston, 1972).
The changes in squawfish behavior were typical of those shown by other
species when shocked with sudden temperature decreases. The "stunned"
behavior has been termed "cold coma:: and is a physiological state relating
to osmoregulatory dysfunction and cessation of opercular movement
(Pitkow, 1960; AlIanson et aI., 1971; Houston, 1972). The fish that
recovered from coma after shocks of lOoC and 150C in this study would
probably not have done so in the. wild. Observers of fish kills caused by cold
sho(l-hm-;~'p~d' lh~l-;t~nne~r fish became stranded in shallow water,
where they were easily preyed upon by birds and unaffected fish. Uneaten
fish that settle to the bottom can become covered with settling solids
(Coutant, 1977). Acute cold stress caused increased predation on 45-mm-
long largemouth bass (Micropterus salmoides) and 40-mm-long bluegills
(Lepomis macrochirus) by unstressed largemouth bass, probably because the
swimming ability of shocked fish was reduced (Coutant et aI., 1974; Wolters
and Coutant, 1976). Water temperatures near 60C allowed largemouth bass
to prey on cold-stunned tilapia (Tilapia aurea) in an Arizona reservoir
(Wanjala and Tash, 1983). -
Others have reported responses of wild fish populations to rapid
temperature decreases caused by weather, streamflow, and reservoir releases.
Chittender (1972) found that young American shad (A losa sapidissima)
were not killed by temperature decreases from 240C to 120C in 1.25 h, but
speculated that reservoir releases of cold water may have caused shad to
abandon affected nursery areas. Larimore and Duever (1968) found that
rapid temperature changes from 280C to 120C in Missouri streams were not
lethal to small mouth bass (Micropterus doLomieui) but may have affected
fish distribution by reducing the ability of the fish to maintain position.
The year-class strength of northern pike (Esox Lucius) may be reduced when

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