The influence of metabolic effects on stable hydrogen isotopes in tissues of aquatic organisms

Abstract

A steady-state mass-balance model describing controls on the stable hydrogen isotopic ratios (δ2H) of tissues in fish was previously developed but physiological effects related to fish size and growth had not been tested. Here, we assessed the influence of size (or growth rate) on tissue δ2H composition of a fish species (Poecilia reticulata) and the incorporation of metabolic products derived from dietary lipids (water, NADH). Sampled tissues were obtained from individuals that grew at different rates while raised on an isotopically homogeneous commercial diet (lipid-free fraction, δ2H=−95±2 ‰; and dietary lipids,−198±11 ‰) under different controlled water hydrogen isotopic composition (δ2H=−128±3 ‰;+17±5 ‰; and+202±5 ‰). Our findings suggested that fish growth rate was correlated positively with the degree of incorporation of metabolic products from dietary lipids that, in turn, influenced both fish tissue protein and lipid δ2H values. We conclude that δ2H measurements of lipids (and, subsequently, of body water) in fish could become a physiological tool that provides insights into fish growth rates.