High thermal tolerance of a rainbow trout population near its southern range limit suggests local thermal adjustment

Abstract

California is the southern limit for indigenous rainbow trout. We studied wild-caught, Endangered Species Act (ESA)-listed fish beside their home stream and showed that the thermal aerobic performance capacity of these fish remains at 95% of peak aerobic scope across temperatures of 17.8–24.6°C. This range represents an unusually high temperature tolerance compared with conspecifics and congeneric species from northern latitudes.

Unusual aerobic performance at high temperatures in juvenile Chinook salmon,Oncorhynchus tshawytscha

“…Thus, experiments examining acclimation temperatures >19°C are certainly warranted for this stock of Chinook salmon. Thermal insensitivity of AAS has been documented previously in another Californian Oncorhynchus species; hatchery Oncorhynchus mykiss aerobic scope was maintained between 16 and 25°C (Verhille et al ., 2016), and wild-caught O. mykiss tested on the Lower Tuolumne River was similar (Verhille et al ., 2015). Again, O. mykiss mortality was evident post-exercise only at 25°C.…”

A rainbow trout Oncorhynchus mykiss strain with higher aerobic scope in normoxia also has superior tolerance of hypoxia

“…Intraspecific differences in metabolic rate, aerobic scope, critical oxygen level, hypoxia tolerance and upper thermal tolerance are not novel observations in fish generally and several previous studies have assessed at least one of these traits in domestic or wild strains of O. mykiss from the U.S.A., Canada, Austria, Italy, Australia and Japan (Fry, ; Bidgood & Berst, ; Klar et al., ; Lee & Rinne, ; Wieser et al., ; Scarabello et al., ; Strange et al., ; Alsop & Wood, ; Currie et al., ; McGeer et al., ; Myrick & Cech, , ; Carline & Machung, ; Faust et al., ; Molony et al., ; Rodnick et al., ; Ineno et al., ; Galbreath et al., ; LeBlanc et al., ; Recsetar et al., ; Chen et al., ; Scott et al., ; Verhille et al., ). In particular, these studies have demonstrated substantial variation in upper thermal tolerance, hypoxia tolerance, routine O 2 and O 2max in O. mykiss , which could be indicative of a large amount of intraspecific variation in this species.…”

Black spot infection in juvenile steelhead trout increases with stream temperature in northern California

“…Overall, the South Fork Eel River, California experiences warmer temperatures than the West Fork Smith River, Oregon (average seven-day maximum of 22.8°C in the SFER (this study) vs 19.3°C (Rodnick et al 2008)), suggesting that the more southern salmonids experience warmer temperatures overall may have adjusted to their thermal habitat through local adaptation and increased resistance to parasites. Such local adaptation in salmonids to warm waters is not without precedent (e.g., Verhile et al 2016). This possibility of local adaptation to thermal regime could provide another reason to conserve salmonids at the southern end of their range as a valuable genetic reservoir for persisting in a changing world (Katz et al 2013).…”