ACTIVITY AND METABOLISM OF LARVAL ATLANTIC COD (GADUS-MORHUA) FROM SCOTIAN SHELF AND NEWFOUNDLAND SOURCE POPULATIONS

Patterns of activity and metabolism were investigated in larval Atlant ic cod (Gadus morhua L.) between December 1991 and July 1992: (1) thro ughout larval development; (2) between two genetically discrete popula tions (Scotian Shelf and Newfoundland) and (3) as a function of two di fferent culture temperatures. During the yolk-sac stage (0 to 5 d post -hatch), changes in swimming speed were not related to mass-specific m etabolic rates; no portion of the mass-specific oxygen consumption cou ld be explained by changes in activity. In the ''mixed feeding'' stage (6 to 14 d posthatch), there was a tendency for oxygen consumption to be related to changes in swimming speed. In the ''exogenous feeding'' stage( > 14 d post-hatch), oxygen consumption significantly increased with swimming speed. These ontogenetic patterns of activity and metab olism were the same for larvae from the Scotian Shelf and Newfoundland populations. However, over the entire larval life and among ontogenet ic stages, the metabolic cost of activity (Delta mass-specific O-2 con sumption/Delta swimming speed) of Scotian Shelf larvae was significant ly higher than that of Newfoundland larvae. When cod larvae, that had developed at 5 degrees C, were acutely exposed to 10 degrees C, Scotia n Shelf larvae had a higher intrinsic cost of activity than Newfoundla nd larvae, over the entire larval life. During the exogenous feeding s tage, the mean metabolic cost of activity for Newfoundland larvae rais ed at 10 degrees C and tested at 10 degrees C was significantly higher and more variable than that of larvae raised at lower temperatures. H owever, the metabolic cost of activity of larvae raised and tested at 10 degrees C was not significantly different between source population s. Together these findings suggest that differences in swimming energe tics reflect changing energy requirements for activity among ontogenet ic stages, and reflect adaptation to regional environments among genet ically discrete populations.