Catadromous refers to fish species that migrate from freshwater to saltwater to spawn. This behavior is most commonly seen in species like eels, particularly the European eel and American eel. These fish live most of their lives in rivers and lakes but travel to the ocean to reproduce. The term contrasts with "anadromous," which describes fish that migrate from saltwater to freshwater for spawning. Catadromous fish typically have a life cycle that includes both freshwater and marine environments, highlighting their unique adaptations to different habitats throughout their lives.