Measurements of larval Atlantic cod (Gadus morhua) routine metabolism: temperature effects, diel differences and individual-based modeling

In the present study, dry mass (MD, μg) and routine respiration rate (RR) (μl O2 ind−1 h−1) were measured for larval cod, Gadus morhua (L.) that were reared and tested at 5.0, 7.5, and 10.0°C. Bi-hourly measurements of RR were made on groups of larvae using a closed-circuit respirometer over a 24-h period (14L : 10D light regime) to test temperature and body size effects and whether unfed larvae exhibited diel differences in metabolism. At 10°C, the relationship between mean RR and mean MD was: ln RR = 1.16·lnMD − 6.57 (n = 31, r2 = 0.883, P < 0.001). The exponential increase in RR with temperature was described by a Q10 of 3.00. Diel differences in unfed larvae were only apparent in groups of the largest larvae. A comparison of Q10 estimates from this and other studies suggest a linear decrease in the effect of temperature on cod RR with increasing log MD for sizes encompassing larvae to large juveniles. The trend may explain, in part, observations of cod juveniles exploiting a wider range of in situ temperatures than larvae. Finally, the two most comprehensive data sets on larval cod RR compare poorly (approximately five-fold differences) and our results support the assertion that daily metabolic energy loss in many larval cod individual-based models were based upon measurements that over-estimated hourly metabolic rates by a factor of approximately four.