Patterns of stable carbon isotope turnover in gag, Mycteroperca microlepis, an economically important marine piscivore determined with a non-lethal surgical biopsy procedure
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To determine the feasibility of using stable isotopes to track diet shifts in wild gag, Mycteroperca microlepis, populations over seasonal timescales, we conducted a repeated measures diet-shift experiment on four adult gag held in the laboratory. Fish were initially fed a diet of Atlantic mackerel, Scomber scombrus, (mean δ13C = −21.3‰ ± 0.2, n = 20) for a period of 56 days and then shifted to a diet of pinfish, Lagodon rhomboids, (mean δ13C = −16.6‰ ± 0.6, n = 20) for the 256 day experiment. We developed a non-lethal surgical procedure to obtain biopsies of the muscle, liver, and gonad tissue monthly from the same four fish. We then determined the δ13C value of each tissue by isotope ratio mass spectrometry. For the gonad tissue we used the relationship between C/N and lipid content to correct for the influence of lipids on δ13C value. We observed a significant shift in the δ13C values of all of the tissues sampled in the study. Carbon turnover rates varied among the three tissues, but the shift in diet from mackerel to pinfish was clearly traceable through analysis of δ13C values. The turnover rates for muscle tissue were 0.005‰ day−1, and for gonad tissue was 0.009‰ day−1. Although it is generally thought that tissue turnover rates in ectotherms are driven primarily by growth, we found that metabolic rate can be a major factor driving tissue turnover in adult gag.
KeywordsBiopsies Surgery Lipid correction Trophic shift
We are grateful to Captain W. Sauls, Panama City, FL, for the use of the F/V Margie Anne for our research; to Captain D. Sauls and crew for assistance onboard in the field; to staff of the Florida State University Coastal and Marine Laboratory (FSUCML), particularly D. Tinsley, B. Henderson, M. Daniels, F. Lindamood, and FSUCML Academic Diving Program for assistance in many aspects of this study; to the Florida State High Magnetic Field Laboratory especially Y. Xu for her assistance with the mass spectrometry, to K. Kingon and N. Hyams (Florida State University) for their assistance in the laboratory; This work was funded through the Northern Gulf Institute, a NOAA Co-operative Institute, NOAA MARFIN NA07NMF4330120 (to Coleman and Koenig), and NOAA Cooperative Research Program NA04NMF4540213 (to Koenig and Coleman).
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