Meeting Abstract
Rainbow smelt (Osmerus mordax) display an impressive ability to acclimate to very cold water temperatures. These fish express both anti-freeze proteins and glycerol in their plasma, liver, muscle and other tissues to avoid freezing at sub-zero temperatures. Further, these fish must feed actively in this cold water to maintain osmolyte levels. We explored smelt muscle function in winter through: (1) thermal acclimation studies on smelt swimming performance, muscle contractile properties and muscle protein expression; and (2) muscle mechanics experiments that evaluated the influence of osmolytes on muscle function. The thermal acclimation studies demonstrated a strong influence of cold acclimation on swimming performance, with cold acclimated fish able to swim at higher sustained swimming speeds but at perhaps higher energetic costs than warm acclimated fish. These cold-acclimated fish had faster contractile properties in both their fast- and slow-twitch myotomal muscle and corresponding shifts in myosin content in both muscle types. The mix of osmolytes in the myotomal muscle of cold-acclimated fish influenced muscle contractile properties. One of the osmolytes that is elevated in winter smelt, trimethylamine oxide, appears to lead to increased force and power production by fast-twitch muscle. Other osmolytes elevated in these fish in winter, such as urea and glycerol, negatively influence muscle function. The thermal acclimation response of smelt in winter must overcome both the effects of cold temperatures as well as the negative effects of increased osmolyte levels on muscle function.
