Aerobic scope for activity in age 0 year Atlantic cod Gadus morhua
Key components of swimming metabolism: standard metabolism (Rs), active metabolism (Ra) and absolute aerobic scope for activity (Ra–Rs) were determined for small age 0 year Atlantic cod Gadus morhua. Gadus morhua juveniles grew from 0·50 to 2·89 g wet body mass (MWB) over the experimental period of 100 days, and growth rates (G) ranged from 1·4 to 2·9% day−1, which decreased with increasing size. Metabolic rates were recorded by measuring changes in oxygen consumption over time at different activity levels using modified Brett-type respirometers designed to accommodate the small size and short swimming endurance of small fishes. Power performance relationships were established between oxygen consumption and swimming speed measurements were repeated for individual fish as each fish grew. Mass-specific standard metabolic rates ( R- s M- WB − 1 ) were calculated from the power performance relationships by extrapolating to zero swimming speed and decreased from 7·00 to 5·77 mol O2 g−1 h−1, mass-specific active metabolic rates ( R- a M- WB − 1 ) were calculated from extrapolation to maximum swimming speed (Umax) and decreased from 26·18 to 14·35 mol O2 g−1 h−1 and mass-specific absolute scope for activity was calculated as the difference between active and standard metabolism ( R- a M- WB − 1 − R- s M- WB − 1 ) and decreased from 26·18 to 14·35 mol O2 g−1 h−1 as MWB increased. Small fish with low Rs had bigger aerobic scopes but, as expected, Rs was higher in smaller fish than larger fish. The measurements and results from this study are unique as Rs, Ra and absolute aerobic scopes have not been previously determined for small age 0 year G. morhua.