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

In the present study, dry mass (M-D, mu g) and routine respiration rate (R-R) (mu l O-2 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 degrees C. Bi-hourly measurements of R-R 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 degrees C, the relationship between mean R-R and mean M-D was: ln R-R = 1.16 center dot lnM(D) - 6.57 (n = 31, r(2) = 0.883, P < 0.001). The exponential increase in R-R with temperature was described by a Q(10) of 3.00. Diel differences in unfed larvae were only apparent in groups of the largest larvae. A comparison of Q(10) estimates from this and other studies suggest a linear decrease in the effect of temperature on cod R-R with increasing log M-D 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 R-R 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.