Specific swimming speeds (L sec-1 ) of spotted seatrout (Cynoscion nebulosus) were linearly related (S = -0.16+0.93X) to tail·beats/sec (x) over speeds ranging from about 1.5 - 4.0 length/sec. Maximum sustained swimming speeds were measured at salinities ranging from 10 to 45 ppt in intervals of 5 ppt. At about 20 to 25 ppt, maximum sustained swimming speeds were close to 4 lengths/sec, but performance was reduced at salinities above or below this range. At 45 ppt, maximum sustained speeds were only about 2 lengths/sec. These results indicate that maximum sustained swimming perform3. p.ce can provide an effective method for evaluating salinity stresses.