Meeting Abstract

P2.167  Tuesday, Jan. 5  Regional Patterns of Muscle Blood Flow During Steady Swimming in Trout GERRY, S.P.**; ELLERBY, D.J.; Wellesley College; Wellesley College sgerry@wellesley.edu

Sustained undulatory swimming in fishes is powered by slow myotomal muscle. Rainbow trout, Oncorhynchus mykiss, are sub-carangiform swimmers with undulations confined to the posterior two-thirds of the body axis. Skeletal muscle performs a number of roles during swimming in addition to mechanical power production, e.g. maintaining stability by controlling fin shape and orientation and powering respiratory movements. The relative energetic costs of these functions are not known. The rate of blood flow to muscle tissue is proportional to its aerobic energy expenditure. Therefore, regional blood flow to specific categories of muscle can be used to indicate their relative functional costs. We hypothesized that during steady swimming blood flow would be concentrated at the myotomal muscles, with less flow to the respiratory, pelvic and pectoral girdle and fin ray muscles. Fluorescent microspheres were injected into the trout systemic circulation via a dorsal aortic cannula at rest and swimming at speeds of 50%, 75% and 100% Ucrit. Following dissection, body tissues were digested to recover the microspheres and quantify their distribution. Over two-thirds of the total muscle blood flow was to the slow myotomal muscles at all swimming speeds. Furthermore, blood flow per gram of muscle mass increases three to four-fold from anterior to posterior myotomes. The fin ray, pelvic and pectoral girdle muscles receive less than one-quarter of total muscle blood flow. The respiratory muscles receive less than five percent of total blood flow, which may indicate a transition from branchial pumping to low-cost ram ventilation during swimming. Future studies will integrate muscle activation and mechanical performance data.