The effects of temperature, body size and growth rate on energy losses due to metabolism in early life stages of haddock (Melanogrammus aeglefinus)

Rates of routine respiration (RR, mu l O-2 fish(-1) h(-1)) and total ammonia nitrogen excretion (ER, mu g NH4- N + NH3-N fish(-1) h(-1)) were measured on larval and juvenile haddock (Melanogrammus aeglefinus) to ascertain how energy losses due to metabolism were influenced by temperature (T), dry body mass (M-D, mg) and specific growth rate (SGR,% per day). R-R and E-R increased with M-D according to y = a . M-D(b) with b-values of 0.96, 0.98, 1.14, and 0.89, 0.78, 0.74, respectively, at 10, 7, and 4 degrees C, respectively. Multiple regressions explained 98% of the variability in the combined effects of MD and T on RR and E-R in larval haddock: R-R = 0.97 . M-D(0.98) . e (0.092) (. T); E-R = 0.06 . M-D(0.79) . e (0.092 . T). In young juvenile (24-30 mm standard length) haddock, R-R tended to decline (P = 0.06) and E-R significantly declined (P = 0.02) with increasing SGR. O: N ratios significantly increased with increasing SGR suggesting that N was spared in relatively fast-growing individuals. Our results for young larval and juvenile haddock suggest: (1) nearly isometric scaling of R-R with increasing body size, (2) allometric scaling of E-R with increasing body size, (3) Q(10) values of 2.5 for both R-R and E-R, (4) metabolic differences in substrate utilization between relatively fast- and slow-growing individuals, and (5) that rates of routine energy loss and growth were not positively related. The measurements in this study will provide robust parameter estimates for individual-based models that are currently being utilized to investigate how variability in climatic forcing influences the vital rates of early life stages of haddock. Our results also stress that inter-individual differences in rates of energy loss should not be overlooked as a factor influencing growth variability among individuals.