Comparison Of Growth And Stress In Resident Redband Trout Held In Laboratory Simulations Of Montane And Desert Summer Temperature Cycles

Transactions of the American Fisheries Society 139:339–352, 2010 American Fisheries Society 2009 DOI: 10.1577/T08-247.1

[Article]

Comparison of Growth and Stress in Resident Redband Trout Held in Laboratory Simulations of Montane and Desert Summer Temperature Cycles
JOHN D. CASSINELLI1
AND

CHRISTINE M. MOFFITT*

U.S. Geological Survey, Cooperative Fish and Wildlife Research Unit,Department of Fish and Wildlife Resources, University of Idaho, Moscow, Idaho 83844-1131, USA Abstract.—Within their native range in western North America, resident redband trout Oncorhynchus mykiss gairdneri occupy stream habitat from high mountains to low desert. To better understand the temperature tolerance, growth, and stress physiology of native redband trout populations and compare theresilience and responses to reciprocal environments of stocks adapted to desert or montane conditions, we conducted controlled laboratory trials. We tested groups of age-0 progeny from naturally reproducing desert and montane fish stocks in temperature cycles that simulated the summer conditions typical in regional desert and montane stream habitats. The diel cycles ranged from 88C to 168C for montanetreatments and from 188C to 268C for desert treatments, and our tests were repeated over 2 years. We evaluated survival, growth, feed efficiency, plasma cortisol, heat shock protein levels, and body proximate composition in samples of fish collected during and at the completion of the trials. All of the stocks tested had high survival under all conditions, regardless of their geographic origin. Wefound no differences consistently attributable to desert or montane origin. Growth rates and protein and lipid efficiencies varied among stocks, between temperature treatments, and between replicate years. We found that the expression of heat shock protein 70 (hsp70) was consistently higher in all stocks maintained at desert temperatures regardless of source, but the absolute quantity of proteinsmeasured varied among populations. We conducted an additional short-term trial to evaluate the responses of different stocks to upper lethal temperature cycles that approached a daily maximum of 308C. Although desert- and montane-adapted populations of redband trout were equally dynamic and adaptive in desert or montane diel temperature cycles, we conclude that the desert stocks will be more atrisk from increasing temperatures and reduced stream flows in the summer months as climate changes.

Rainbow trout Oncorhynchus mykiss are native to western North America and their appropriate phylogeny and taxonomy is unresolved (e.g., Behnke 1992; Currens et al. 2007; Thurow et al. 2007). Native rainbow trout occurring east of the Cascade Range within the Columbia River basin are classified asredband trout O. mykiss gairdneri (Behnke 1992). In southern Idaho, Columbia River basin resident redband trout are native to the Snake River sub-basin below Shoshone Falls, and occupy habitat from high elevation, cool mountain streams to low elevation, desert streams (Schill et al. 2007). During months of low flow in desert environments, afternoon water temperatures can reach 328C for short periods(Idaho Department of Fish and Game, unpublished data). Various studies report the upper critical temperatures for strains of rainbow trout as 26.9–29.88C, depending on acclimation temperature
* Corresponding author: cmoffitt@uidaho.edu 1 Present address: Idaho Department of Fish and Game, Nampa Research Office, 1414 East Locust Lane, Nampa, Idaho 83686-8451, USA. Received December 22, 2008;accepted September 11, 2009 Published online December 31, 2009

(Lee and Rinne 1980; Currie et al. 1998; Beitinger et al. 2000). However, Behnke (1992) and Zoellick (1999) both found actively feeding desert redband trout in water temperatures of 26–288C and both investigators have suggested that desert redband trout may have evolved unique physiological mechanisms that enable them to withstand...