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Exotic fishes dominate protected Las Estacas spring in Morelos

A new study published in Frontiers in Fish Science examines the fish community of Las Estacas, a spring-fed stream in Morelos, central Mexico, and finds that introduced fishes now dominate this protected freshwater ecosystem. “The fish assemblage of a Mexican protected spring system dominated by exotic fishes” was authored by Topiltzin Contreras-MacBeath, Masiel Moreno Romero, Humberto Mejía Mojica, Juan Manuel Rivas González, Juan Carlos Sandoval Manríque, Juan Alberto Hernández Arias, and Enrique González Gavito. ffm01346

Snorkel surveys conducted in 2023 recorded 4,521 fishes representing 14 species, but only four were native to the Balsas River basin: Astyanax aeneus, Amphilophus istlanus, Ictalurus balsanus and Poecilia sphenops. The remaining ten species were exotic, and introduced fishes accounted for about 70% of all individuals. The assemblage was dominated by Xiphophorus hellerii (22.5%) and Amatitlania nigrofasciata (21%), followed by the native Poecilia sphenops and Astyanax mexicanus, each representing about 15%.

Notably, 80% of the exotic species originated from ornamental aquaculture, reflecting Morelos's role as a center of ornamental fish production and the risks posed by fish-farm escapes. The native cichlid Amphilophus istlanus and Balsas catfish Ictalurus balsanus were both exceptionally scarce.

The study provides an important baseline for a newly funded “Rewilding Las Estacas” program, which aims to restore a fish community dominated by native species through habitat management, control of exotic fishes, reintroduction of native species, and environmental education.