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Temperature tolerance of green sunfish (Lepomis cyanellus).

Article Excerpt
Abstract.-Mean ([+ or -] SD) critical thermal maxima of green sunfish (Lepomis cyanellus) acclimated from 10 to 35[degrees]C ranged from 33.5[+ or -]0.83[degrees]C to 41.3[+ or -]0.26[degrees]C while the critical thermal minima of individuals acclimated over the same temperatures extended from 0.2[+ or -]0.28[degrees]C to 11.2[+ or -]0.73[degrees]C. Temperature tolerance was significantly related to acclimation temperature and the latter accounted for a majority of variation in both lower (97%) and upper (98%) temperature tolerance. A measured upper lethal temperature of 41.3[degrees]C and estimated temperature tolerance polygon of 1270[degrees][C.sup.2] confirm that the green sunfish is among the most eurythermal native North American fish species. The tolerance polygon was partitioned into low and high temperature acclimation dependent areas of 384 and 205[degrees][C.sup.2], respectively, and when combined, essentially doubled the tolerance area from 618 to 1270[degrees][C.sup.2]. The low temperature acclimation dependent area is approximately 1.4 times larger than the high temperature dependent area, suggesting that acclimation has a greater effect on tolerance of lower temperatures. The overall temperature tolerance ability of green sunfish may play an important role in this species ability to cope with global climate change.

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Green sunfish (Lepomis cyanellus) are native to the U.S. central plains between the Appalachian and Rocky Mountains, south to the Gulf Coast and north to the Great Lakes (Pflieger 1997). They are distributed throughout Texas and the U.S. with exceptions of Florida and parts of the northwest. The successful spread of green sunfish has been aided by their tolerance of physical/chemical variables (Smale & Rabeni 1995) which is an outcome of their origin and evolution within environmentally variable Great Plain streams. For example, water temperature in Great Plain streams reach 0[degrees]C in winter, and summer temperatures of 40[degrees]C have been reported (Matthews & Zimmerman 1990). Although a few studies (see Table 1) have presented upper temperature tolerances of green sunfish at selected acclimation temperatures; neither low temperature tolerance data nor a temperature tolerance polygon across a range of acclimation temperatures has been published for this species.

Table 1. CTMaxima (Mean [+ or -] SD) of green sunfish. Entries include acclimation temperature, rate of temperature change during trials, test endpoint (Loss Of Equilibrium or Onset of Muscle Spasms) and source. [T.sub.ACCL] [DELTA]T Endpoint CTMax Source ([degrees]C) ([degrees]C ([degrees]C) [min.sup.-1]) 25 0.3 LOE 37.4[+ or -]0.53 Carveth et al. (2004) 30 0.3 LOE 40.2[+ or -]0.50 Carveth et al. (2004) 26 0.017 LOE 37.9[+ or -]0.75 Smale & Rabeni (1995) 10 1.0 LOE 31.1[+ or -]1.45 Lutterschmidt & Hutchison (1997a) 10 1.0 OMS 34.2[+ or -]2.06 Lutterschmidt & Hutchison (1997a) 20 0.3 LOE 35.8+0.69 Carrier & Beitinger (1988) 20...

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