Terrestrial Carbon Additions to Zooplankton Prey Influence Juvenile Estuarine Fish Growth

Abstract

Freshwater inflows are linked to the abundance and catch rates of fish in estuaries. The role of terrestrial carbon resources brought into estuaries after inflows may be important, but this is currently not well understood. Therefore, we performed a study examining the effect of terrestrial dissolved organic matter (tDOM) dietary additions on the growth of food-limited juvenile Australian bass (Macquaria novemculeata). Crustaceous zooplankton Artemia franciscana (Artemia) were reared for two days under control conditions (no addition) or with additions of tDOM leachate at dissolved organic carbon (DOC) concentrations of 5 mg/L or 10 mg/L. Artemia were fed to juvenile bass in their treatment tanks over 42 days at feeding rates reduced by 65–75% of ad libitum. Juvenile fish from the 5 mg/L treatment exhibited no statistical difference in weight or standard, fork and total lengths compared to the control treatment. In contrast, the fish in the 10 mg/L tDOM treatment had significant increases (p < 0.05) in all length parameters after 42 days compared to the other treatments. The greater lengths of fish where tDOM is available indicate that tDOM can contribute to improved growth and development in juvenile Australian bass. While stable isotope analysis of fish tissue showed only minor changes toward terrestrial carbon signatures, increased terrestrial resource availability in the juvenile fish diets may have subsidised energetic needs, facilitating the greater utilisation of endogenous resources. Overall, the results indicate that freshwater inflows that deliver terrestrial resources may be important for the growth and development of estuarine fish.