Environmental flows, which aim to reinstate or protect key aspects of a rivers natural flow regime, are now considered an essential ingredient to maintain or restore native fish populations in flow degraded rivers. Optimising the benefits of environmental water delivery for fishes is currently reliant on restoring key aspects of the natural flow regime governing population processes. Unfortunately, for many of Australia’s freshwater fish species, there is still much uncertainty surrounding many of these vital links, making environmental flow recommendations and subsequent predictions of responses difficult.
Conceptually, the pathway by which flow is frequently linked to the governance of fish populations is through its influence on habitat availability, connectivity and key ecological processes affecting fish condition and growth. Fish condition and growth has been demonstrated to influence each of the key population processes governing fish populations including recruitment, survival and movement.

We investigate the growth of several species of native fish under a range of flow conditions in two rivers of the southern Murray-Darling Basin. Biochronology techniques were used to reconstruct fish growth in the unregulated Ovens River and regulated Murray River over a 23 year period encompassing major drought, flood and for the Murray River, environmental water delivery. Our results are used to predict the influence of previous environmental water deliveries on fish growth and strategies to improve such deliveries to maximise any such benefits for fish.