Global patterns of fish–macrocrustacean interactions in freshwater environments: a systematic review

Esli Emanoel Domingues Mosna, Josie South, Jansen Zuanon, Alison Wunderlich, Célio Magalhães, Marcelo Antonio Amaro Pinheiro, João Henrique Alliprandini Costa

1. Understanding species interactions is central to ecology, yet they remain one of the least documented dimensions of biodiversity (the Eltonian shortfall). Most studies have focused on terrestrial vertebrates, while aquatic vertebrates and invertebrates are still poorly understood. Here, we assessed broad patterns in the published literature on interactions between fishes and macrocrustaceans in freshwater ecosystems, identifying the main interaction types, habitat, and major geographical and taxonomic gaps.
2. We conducted a systematic literature review using the Scopus database, including articles published up to December 2025, and identified 96 eligible studies conducted in freshwater environments. We classified studies according to interaction type, habitat, country and taxonomic group, and quantified research effort through number of publications.
3. The retrieved literature focused primarily on predation, followed by parasitism, competition, and commensalism, and was conducted mainly in streams, lakes and rivers, whereas wetlands were markedly underrepresented. In absolute terms, studies were concentrated in the United States, Brazil, and Canada. When publication counts were standardised by national land area, the highest values were recorded for Trinidad and Tobago, Puerto Rico, and Czechia. Most studies involved native fishes and native macrocrustaceans, although interactions between native fishes and non-native macrocrustaceans formed the second most frequent category.
4. These patterns may reflect historical, methodological, and ecological biases, including the predominance of trophic approaches, the greater practical accessibility (e.g., logistical issues) of certain habitats, and the influence of established model systems.
5. Our results highlight a pronounced Eltonian shortfall in freshwater ecosystems. Expanding research across neglected habitats, interaction types, and taxa, as well as conducting more direct field observation studies, will be essential to improve our understanding of biodiversity interaction dynamics and predictions of ecological responses to global environmental change.