Assessing the Thermal Tolerance and Growth Potential at Elevated Temperatures of Three Different Strains of Rainbow Trout (Oncorhynchus mykiss)

Abstract

Assessing the Thermal Tolerance and Growth Potential at Elevated Temperatures of Three Different Strains of Rainbow Trout (Oncorhynchus mykiss) Michael A. Porto This thesis examines how critical thermal maxima (CTM) differs between different strains of rainbow trout (Oncorhynchus mykiss) and explores the relationship between thermal tolerance and consumption, conversion efficiency, and growth rates at elevated temperatures. This thesis is comprised of three chapters; (1) an introduction and literature review on studies of temperature tolerance and growth in salmonids, (2) an experimental study investigating the CTM of three different strains of rainbow trout, and (3) an experimental study investigating the correlation between thermal tolerance and consumption, food conversion efficiency (FCE) and growth at elevated temperatures. For the first experimental study, we quantified the CTM of the Kamloop, Wytheville and Case Western strains of rainbow trout. The Case Western strain was of particular interest to us because it was thought to possess a higher thermal tolerance than other common strains of trout. We found that there were significant differences between the CTMs of the three strains and that the Case Western stain did have a higher thermal tolerance than the Kamloop and Wytheville strains (Mann-Whitney U; p < 0.003). We also found a significant positive correlation between CTM and condition factor (linear regression; p < 0.001). In the second study, we determined consumption, FCE, and growth rates at temperatures of 20 and 22:C for individuals who's CTMs had previously been determined. We found that there were significant differences between the consumption, FCE, and growth rates of the three strains at both temperatures (Two-way ANOVA; p < 0.001). In general, the Case Western strain consumed, converted less efficiently, and grew less than the other two strains at both temperatures. We also found no significant correlations between individual CTM and consumption, FCE, or growth at either temperature. There was a slight trend in these correlations however. As individual CTM increased, consumption, FCE, and growth rates tended to decrease. This may indicate some tradeoff between the ability to survive and grow at these stressful temperatures.

Genetic Basis for Thermal Tolerance in Two Different Strains of Rainbow Trout (Oncorhynchus mykiss): Case Western and Kamloops

“…The Case Western strain is considered the only warm water trout, only recently was any aspect of its thermal tolerance quantified. Porto (2012) determined critical thermal maxima (CTM) for the Case Western strain and found it to be about 0.15 °C higher than the Kamloops strain. This thesis is comprised of three chapters:…”

“…Therefore the Case Western life history brings up the inquiry of whether this particular strain truly does possess this thermal tolerance it was thought to have or if it has been lost due to a lack of selective pressure that has not been enforced. Porto (2012) did a recent study where actual thermal tolerance of the Case Western rainbow trout was documented and compared to other common strains in a controlled laboratory setting, and an additional aquaculture setting. My study will focus on identifying two thermal regulating genes responsible for the higher thermal tolerance of the Case Western rainbow trout (HSP70 and HSP90).…”

“…The Case Western strain is considered the only warm water trout, only recently was any aspect of its thermal tolerance quantified. Porto (2012) determined critical thermal maxima (CTM) for the Case Western strain and found it to be about 0.15 °C higher than the Kamloops strain. This thesis is comprised of three chapters: (1) an introduction and literature review on the biological history of these two strains of rainbow trout, on studies related to HSPs expression as indicators of thermal tolerance, and studies on the relation between cortisol expression and HSPs expression; (2) an experimental study investigating the differences between HSP70 and HSP90 between the two strains, before and after a heat stress test and between individuals of different sizes; (3) an experimental study investigating the relation between the heat stress protein expression and cortisol levels pre-and post-stress.…”

“…Since the strain was sold in the early 1990's to Laurel Hill Trout Farm, Inc. (Somerset, PA, United States), there has been only one study related to thermal tolerance done on the individuals of this strain, and none involving physiological stress responses. Porto (2012) conducted laboratory experiments and determined that the Case Western strain had a 0.15 o C higher critical thermal maximum (CTM) than the Kamloops strain. Such a small difference in CTM among these strains brings up the question of whether this particular strain truly does possess the thermal tolerance it was thought to have, or if it has been lost due to a lack of selective pressure.…”