Endurance at intermediate swimming speeds of Atlantic mackerel, Scomber scombrus L., herring, Clupea harengus L., and saithe, Pollachius virens L.

Endurance and swimming speed were measured in mackerel, herring and saithe when they were induced by the optomotor response to swim at prolonged speeds along a 28-m circular track through still water in a 10-m diameter gantry tank. The maximum sustained swimming speed (Ums was measured as body lengths per second (b.l.s−1) for each species and for saithe of different size groups. Herring with Ums of 4.06 b.l.s−1 (25.3 cm, 13.5°C) were the fastest, mackerel Ums was 3.5 b.l.s1 (33 cm, 11.7°C) and saithe (14.4°C) showed a size effect where Ums at 25 cm was 3.5 b.l.s1 and at 50 cm 2.2 b.l.s1. When swimming at speeds higher that Ums, all three species showed reduced endurance as speed increased. How the curved track reduces the swimming speed is discussed.