Shared shelter preferences in an endemic and an invasive catfish (Ictalurus balsanus and Ictalurus punctatus)

Shelters are an important component of the spatial niche of many freshwater fishes, providing protection from predators and environmental stressors and influencing patterns of habitat use. When native and invasive species rely on similar refuges, overlap in shelter use may promote competition and affect the structure of aquatic communities. Here, we compared the shelter preferences of juvenile individuals of the endemic Balsas catfish Ictalurus balsanus and the invasive channel catfish I. punctatus . Each individual was presented with four shelter types (Rock, Wood, Algae, and PVC) in a sequential rank-choice experiment that generated a preference hierarchy. Both species exhibited a consistent preference structure. Wood was most frequently selected as the first refuge, followed by Rock, whereas Algae and especially PVC were rarely chosen. Analyses based on full ranking data likewise revealed a strong preference hierarchy (Wood > Rock > Algae > PVC). Despite the invasive status of I. punctatus , shelter preference patterns were broadly similar between species. These results indicate substantial overlap in refuge use between the endemic and invasive catfishes. Because structural refuges can influence survival, resting behavior, and exposure to predators, such overlap could promote competition when preferred shelters are limited in natural habitats. Understanding how native and invasive species use refuges may therefore help clarify potential mechanisms of interaction and inform management strategies in invaded freshwater ecosystems.