Since its introduction in 1955, the largemouth bass, also known as the black bass, has emerged as one of the most formidable threats to Spain’s freshwater biodiversity. Originally brought in by anglers to enhance recreational fishing, this species has expanded its presence across numerous river basins, profoundly affecting native aquatic ecosystems.
Biological invasions rank among the primary drivers of biodiversity loss globally, with freshwater and island habitats being particularly susceptible due to their delicate ecological balances. Spain’s diverse freshwater environments—including rivers, reservoirs, lakes, and lagoons—support a rich variety of native species, many of which now face serious risks from invasive species like the largemouth bass.
Native to the Mississippi River basin in the United States, the largemouth bass was introduced to Spain with the aim of promoting sport fishing. Over the ensuing decades, human-assisted transfers between different river basins facilitated its widespread colonization throughout the country. This expansion led to its official classification as an invasive alien species in Spain’s catalog in 2013. Furthermore, the Global Invasive Species Database recognizes the largemouth bass as one of the top 100 most harmful invasive species worldwide.
Adaptability and Ecological Impact
The largemouth bass owes much of its invasive success to its exceptional adaptability and predatory behavior. Mature individuals can exceed 16 inches in length and exhibit voracious feeding habits, preying on a wide range of aquatic organisms including insects, native fish, and amphibians. This aggressive diet disrupts existing food webs and threatens the survival of indigenous species, thereby altering the structure and function of freshwater habitats.