The fish assemblage of a Mexican protected spring system dominated by exotic fishes

Springs, as sensitive freshwater ecosystems, are particularly vulnerable to anthropogenic factors such as water extraction, pollution, and climate change. Las Estacas spring in Central Mexico, managed as a water park within a state reserve, serves as an ideal space for environmental education and conservation efforts. Snorkel surveys identified 14 fish species, with 70% being invasive and most of these come from ornamental fish. We computed multiple diversity indices and evaluated sampling completeness through rarefaction analysis. The fish assemblage was dominated by Xiphophorus helerii and Amatitlania nigrofasciata with 23% and 21% of the sample respectively, it exhibited moderate diversity (Shannon H’ = 1.955) with relatively even species distribution (Pielou’s J’ = 0.741). Rarefaction analysis confirmed adequate sampling effort, with the curve approaching asymptote at approximately 3,501 individuals (95% of observed richness). The findings provide baseline biodiversity metrics essential for conservation monitoring and ecosystem management. To address this, a rewilding project is now in place, with the goal to establish a fish assemblage dominated by native species through habitat management, exotic species control, native species introduction, and education.