Influence of diet and ambient water on hydrogen and oxygen stable isotope ratios in fish tissue: patterns within and among tissues and relationships with growth rates

The influence of food and ambient water on 2H and 18O isotopic composition in fish soft tissues, how growth affects tissue-specific composition, and relationships of isotope values within and among tissues are poorly known. We exposed age-0 largemouth bass (Micropterus salmoides) to ambient water and food with known δ2H and δ18O values for 65 days and analyzed liver and muscle for δ2H and δ18O levels. Liver δ2H but not δ18O was influenced by water isotopic concentrations and neither ratio was influenced by the isotopic composition of food. In contrast, water and food affected muscle δ2H, whereas muscle δ18O was only influenced by water isotopic values. We observed relationships between fish growth and muscle δ2H and δ18O, where increased growth led muscle to come closer into equilibrium with food and water isotope values, but found no relationships with growth and either liver δ2H or δ18O. Ratios of 2H and 18O were positively related within muscle and within liver of individuals, as were δ2H values between liver and muscle and δ18O values between tissues. Studies assessing 2H and 18O in temperate fishes should account for isotopic contributions from water and food and consider consequences of fish growth and timing of sample collection.