Abstract
The present study compares the stable oxygen-and carbon-isotope ratios (180:16O;13C:12C) in the otoliths of Atlantic cod,Gadus morhua, with those expected at equilibrium with seawater. Otoliths from juveniles reared for a 3 mo period under controlled conditions indicate that otoliths are formed in isotopic disequilibrium with seawater. This is probably due to positive metabolic fractionating of the heavier isotopes. This “vital effect” remains constant over the temperature range studied here (9 to 16°C) but may differ among other species. Our data indicate that the concentration of18O in calcium carbonate is inversely related to temperature and is described as ∂18Oa − ∂w − 3.79 − 0.200(T°C). The13C:12C ratios of otoliths and body tissues are related to the carbon ratio in the food source, although we found that the13C concentration is considerably higher in the otoliths relative te, the body tissues and the diet.
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