MEPS 461:197-209 (2012)  -  DOI: https://doi.org/10.3354/meps09871

ABSTRACT: A 150 d laboratory diet-shift study was conducted on juvenile Atlantic cod Gadus morhua L. to examine (1) stable nitrogen and carbon isotope turnover rates, (2) the tissue-specific relative contribution of metabolism and growth to isotopic change, and (3) diet−tissue enrichment of the isotopes in white muscle, heart, whole blood, and cranial bone collagen. Time- and growth-based models described the change in δ¹⁵N and δ¹³C of the tissues following a diet shift from pelleted food to either blue mussels Mytilus edulis L., sandeel Ammodytes marinus Raitt., or whiting Merlangius merlangus L. diets. Cod growth rates ranged from 1.5 to 2.0% d⁻¹, with the exception of whiting-fed cod that experienced a cessation in growth after Day 86. Isotope turnover rates, expressed as half-lives (T_½), differed little between tissues as expected in fast-growing fish. For δ¹⁵N, heart tissue had the shortest T_½ while muscle had the longest (30.7 to 34.8 versus 35.7 to 77.9 d⁻¹; range among diets). Heart tissue also had the shortest δ¹³C T_½, whereas blood had the longest (25.5 to 38.5 versus 49.5 to 60.3 d⁻¹; range among diets). Diet-tissue enrichment varied between 0.8 and 5.1‰ (Δδ¹⁵N) and between 0.7 and 2.2‰ (Δδ¹³C). Growth accounted for most of the isotopic change, except in heart tissue of all cod and in all tissues of whiting-fed cod, where there was a significant effect of metabolism on isotopic change. Despite variability in enrichment among diets and tissues, fish feeding on the 3 diets could be distinguished based on their tissue-specific isotopic signatures.

KEY WORDS: Isotopic turnover · Diet shift · ¹⁵N · ¹³C · Nitrogen · Carbon · Growth · Metabolism