Assessing the Thermal Tolerance and Growth Rates of Three Different Strains of Rainbow Trout

Temperature has long been known to have numerous effects on trout physiology and survival.  How these effects differ between different strains of the same species is not as well understood.  To better understand this we have determined the thermal tolerance of three different strains of rainbow trout as well as their growth rates at elevated temperatures.  The three strains of trout used in this study were the Kamloop strain, the Case Western strain, and the Wytheville strain.  The Case Western strain was of particular interest because it is thought to have a higher thermal tolerance than most other rainbow trout strains.  Since the strain’s inception however, no one has quantified its thermal tolerance or compared it to other strains of rainbows.  To do this we have determined the critical thermal maxima (CTM) of this strain and compared it to the CTM of the two stock strains. ANOVA results showed differences between the CTM’s of the three strains (p<.001) and it was determined that the Kamloop strain had a significantly higher thermal tolerance than the Case Western strain (p<.001) as well as the Erwin strain (p<.001).  The Case Western strain’s CTM was also significantly higher than that of the Erwin strain (p<.001).  ANCOVA results showed a significant relationship between size and thermal tolerance (p<.001).  As the fish grew larger their thermal tolerance decreased.  Growth was then assessed to determine if individuals with higher thermal tolerances also grew better at elevated temperatures when compared to fish with lower thermal tolerances. Growth rates were assessed at a baseline temperature to detect differences between strains and then again at an elevated temperature.