Effects of temperature, fish length, and exercise on swimming performance of age-0 flannelmouth sucker

The flannelmouth sucker Catostomus latipinnis is one of the few native fish that persists in the lower Colorado River basin. Little is known about the effects of hypolimnetic releases of cold, swift water from Colorado River dams on flannelmouth sucker populations. We conducted fatigue velocity tests on age-0 flannelmouth suckers in the laboratory to evaluate the effects of water temperature and fish size on swimming ability. Fish of 25-114 mm total length (TL) were subjected to incremental increases in water velocity until the upper limit of their swimming ability was reached. Swimming tests were conducted at 10, 14, and 20°C. Swimming ability increased with fish length and was directly related to water temperature at all fish sizes. A decrease in water temperature from 20°C to 10°C resulted in an average decrease in swimming ability of 40%. Mean swimming ability of wild-caught flannelmouth suckers was 7 cm/s higher than that of captive-reared flannelmouth suckers of similar size at 20°C and 14°C. Flannelmouth suckers subjected to an abrupt 10°C temperature drop did not have significantly different swimming ability than flannelmouth suckers acclimated to 10°C over 4 d.