Relationships among Proximate Components and Energy Density of Juvenile Atlantic Estuarine Fishes

Abstract

Information on the energy density of juvenile fishes is needed to inform food web and bioenergetic models. Several approaches may be used to estimate energy density, and although these approaches are expected to yield similar estimates, the accuracy of such estimates has not been assessed. Estuarine fishes have unique life history strategies that influence the water, protein, lipid, and ash composition of their tissues. Because proximate components vary among species, the preferred approaches for estimating energy density from these components may also differ. We investigated the suitability of five approaches to estimate energy density measured by bomb calorimetry from water content for juvenile Summer Flounder Paralichthys dentatus, Striped Bass Morone saxatilis, and Atlantic Croaker Micropogonias undulatus. Approaches were based on the following: (1) relationships between water and percent composition, (2) relationships between water and the mass of proximate components, (3) water content alone (by percentage and by mass), (4) percent water and fish mass, and (5) published relationships between energy density and percent dry weight. The mean predicted energy densities from alternative approaches were generally within 10% of the mean energy densities measured by bomb calorimetry (4.21 kJ/g to 4.94 kJ/g). For Summer Flounder and Atlantic Croakers, regressions based on the percent water from whole fish provided estimates of energy density closest to those from bomb calorimetry, and including fish mass improved the accuracy of energy density estimates for Striped Bass. Energy density calculated from percent composition overestimated measured energy density, even with conservative lipid-to-energy conversion factors; this was most pronounced for individuals with energy densities less than 5 kJ/g. Because lipid-to-energy conversion factors may not be temporally stable or spatially invariant, further research is needed on the energy content of lipid classes in fishes. The types of lipids used for energy storage likely vary among life stages and species, and extrapolating approaches to different size-classes or species groups may bias estimates of energy content.

Received November 26, 2014; accepted April 29, 2015

ACKNOWLEDGMENTS

We thank R. Latour (Virginia Institute of Marine Science [VIMS]), E. Hilton (VIMS), and T. Sutton (Nova Southeastern University) for loaning us the equipment needed to conduct this research, and J. Trushenski (Southern Illinois University) for conducting proximate composition analysis. This study would not have been possible without the help of many individuals who collected specimens, particularly the staff of the VIMS Recruitment Program (H. Brooks, A. Comer, J. Conwell, W. Lowery, L. Machut, L. Nys, R. Norris, and T. Tuckey). Thanks to J. Breck and an anonymous reviewer for their helpful suggestions for improving this manuscript. Virginia Sea Grant, the Virginia Marine Resources Commission, and the VIMS Ziegler Fellowship provided funds to support this research. This paper is Contribution 3479 of the Virginia Institute of Marine Science, College of William and Mary.