Mode of locomotion places selective pressures on Antarctic and temperate labriform swimming fish

The physiological responses to exercise and stress of the Antarctic labriform swimmer Pagothenia borchgrevinki were compared to the temperate labriform swimmers Notolabrus celidotus and Notolabrus fucicola. Basic swimming characteristics were very similar amongst the three species with P. borchgrevinki showing a reduced capacity for exercise. P. borchgrevinki showed large increases in haematocrit (Hct) following exercise that were not seen in the temperate species. Lactate dehydrogenase (LDH) activities were high in the white myotomal muscle from the Antarctic fish, with a distinct indication of metabolic cold adaptation in this enzyme. Nevertheless, although the temperate fish showed elevated muscle lactate concentrations following either exercise or electrical stimulation the Antarctic fish did not. The data suggest that poor anaerobic performance of white muscle is associated with the labriform mode of locomotion.