Distance (m) sea lampreys, (Petromyzon marinus), swam increased with weight (2.4-106.9 g) but at a decreasing acceleration for a fixed velocity and temperature. Distance declinedwith increase in swimming speed between 20-60 cm/sec at a decreasing acceleration. Thegreatest distance was recorded for the largest lampreys at the lowest swimming speeds. Distanceincreased with temperature between 5-15 C. Performance of sea lampreys was less than that forteleosts which may be related to differences in their morphology.