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Some aspects of exercise physiology in fish Kiceniuk, Joe Willie

Abstract

The limiting factors of swimming performance were studied in fish exercising in a water tunnel. The relationship between (10 min) critical velocity and body length determined in 10 species of freshwater teleosts is discussed with respect to the ratio of lateral red body musculature to total body weight. Electromyographic recording from red and white portions of the body musculature in four species of fish showed that red muscle fibers alone are active during steady swimming at sustained speeds. White muscle fibers are active only during bursts of violent swimming, such as during rapid acceleration and for a brief period preceding fatigue. Thus red muscle fibers, generally accepted as having an aerobic metabolism, appear to be the major determinant of sustained swimming speed. To establish the time course of cardiovascular and respiratory changes during swimming; heart rate, ventilation rate, dorsal aortic, ventral aortic, and right common cardinal blood pressures were monitored during steady swimming following abrupt changes in water velocity. Under these circumstances most of the heart rate increase occurred in the first thirty seconds and heart rate did not change further after 3-15 minutes at a given swimming speed. Ventilation rate tended to increase initially and then decline, reaching a constant value after 15-30 minutes at a given swimming speed. Dorsal and ventral aortic blood pressure increased more slowly than heart rate, peaking after six minutes then declining to constant values after about 30 minutes. Blood pressure in the common cardinal vein was constant during exercise. The animals were considered to be in a steady state with regards to these circulatory and respiratory variables after about 30 minutes. Oxygen consumption increased from a mean of 0.58 ml kg⁻¹ min⁻¹ at rest to a mean maximum of 4.34 ml kg⁻¹ min⁻¹. Under the same circumstances cardiac output increased from a mean of 17.6 ml kg⁻¹ min⁻¹ at rest to a mean maximum of 52.6 ml kg⁻¹ min⁻¹. The corresponding stroke volume was 0.46 ml kg⁻¹ stroke⁻¹ at rest and 1.03 ml kg⁻¹ stroke⁻¹. Arterio-venous oxygen difference at rest was 3.29 volumes % and increased to 8.3 volumes % as a result of a decrease in venous saturation (to lower than 10% in some cases) during exercise. Heart rate at rest was 31.75 min⁻¹ and increased during exercise by a mean of 1.33 times. Ventral aortic blood pressure rose from 38.8 Torr at rest to 61.7 Torr. The corresponding ventral aortic pulse pressure rose from 11.6 Torr at rest to 26 Torr. Dorsal aortic mean pressure at rest was 31 Torr and increased to 37 Torr with exercise, accompanied by an increase in pulse pressure from 5.8 Torr at rest to 10 Torr. Ventilatory volume at rest was 211.4 ml kg⁻¹ min⁻¹ and increased to about 1700 ml kg⁻¹ min⁻¹ at maximal sustained swimming speed. The capacity rate ratio of oxygen exchange between water and blood increased from 0.6 at rest to 1.8 during exercise. Arterial blood of resting trout was 97% saturated with oxygen and % saturation did not change with exercise. Blood lactate at rest and at swimming speeds as high as 93% of critical velocity was 0.5 μM/ml. One minute after fatigue the blood lactate level had increased about five fold and continued to increase, reaching a maximum value (6-10 μM/ml) 2 to 2.5 hours after fatigue.

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