Growth and Myosin Heavy Chain Expression in the White Muscle of Juvenile Walleye (Sander vitreus)
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Walleye are an important recreational and commercial fish species that are distributed over an expansive geographic range across North America. However, its palatable white flesh and appeal to anglers have lead to declines in natural populations throughout Canada and the United States. These declines have prompted the idea that aquaculture may serve as a means of satisfying consumer demands and decreasing pressure on wild stocks. While culture programs exist for walleye, little is known about the growth physiology of walleye in a culture system. The goals of this thesis, therefore, were to develop a molecular marker that could be used to rapidly assess growth in juvenile walleye, and to make improvements to culture practices that will optimize growth. To begin, we examined the relationship between growth and the expression of the myosin heavy chain gene (MyHC) in the white muscle of juvenile walleye. The coding region of MyHC from the fast skeletal muscle of walleye was amplified using a full length cDNA. Growth was then characterized using traditional measurements of growth (length, weight and condition factor), as well as MyHC protein concentration and MyHC mRNA levels. Both MyHC mRNA and protein expression were highly correlated with faster growth in juvenile walleye. Over shorter time scales, the MyHC mRNA marker was sensitive enough to detect impacts of fasting that could not be detected using traditional measurements of growth. Next, MyHC mRNA quantification was applied to an aquaculture setting. Feed training is an important bottleneck during juvenile walleye culture that often leads to mortalities and cannibalism. These experiments showed that the brief fasting period during the diet switch from plankton to commercial pellet feed caused a significant decrease in MyHC mRNA levels. Furthermore, the success of feed training in terms of survivorship and growth potential increased significantly for larger fish. The final section of this thesis examined how acute and chronic temperature exposure impacted MyHC mRNA and protein expression. Results showed that the nature of the heat stress can significantly affect the MyHC response. These findings are important as the temperature stresses induced in these studies are common during the summer months in southern Ontario.