Ecosystem-based-management is becoming increasingly common in fisheries. Thus, it is critical to understand how key ecological features such as stability may scale with complexity, ensuring that management targets remain achievable. A well-established ecological principle is that diversity enhances stability, which has been measured in aquatic systems under the framework of the portfolio effect. The portfolio effect has been recorded across a range of biological scales, from within-population variations to metapopulations, and from species to metacommunities. Despite widespread citations of the portfolio effect in aquatic and fisheries literature, empirical tests on the phenomena remain relatively scarce. We reviewed aquatic ecological papers to identify publication trends and examine how these may vary across biological scales. Of 1,221 papers citing the portfolio effect, only 55 formally tested and reported portfolio effect values. Within this group, there was a pronounced spatial and species bias towards diadromous salmonids in northwestern America. Where empirically tested, we found that portfolio values increased as biological complexity also increased. Since no consensus exists outlining strong versus weak portfolio effects, we provide thresholds to guide future applications of this ecological framework. As aquatic systems face rapid environmental change, understanding the mechanisms maintaining stability is vital for effective conservation and management.