Catadrome

Catadrome is a term used in ichthyology to describe the migratory pattern by which certain aquatic species travel from freshwater or estuarine environments to the marine environment in order to spawn. It is the opposite of anadromy, which describes migration from the sea into freshwater to reproduce. In a catadromous life cycle, individuals typically grow to maturity in rivers, lakes, or brackish habitats, then undertake a long downstream migration to the open ocean to spawn.

During reproduction, eggs are released in saltwater and hatch into leptocephalus larvae, which are carried by ocean currents back toward coastal and continental shelf regions. Juvenile fish that enter freshwater habitats then grow to maturity before repeating the cycle. The classic and most well-known example of catadromy is the life cycle of the Anguilla eel species, including the European eel (Anguilla anguilla) and the American eel (Anguilla rostrata).

Geographic distribution of catadromous species is broad, encompassing temperate regions in Europe, North America, and parts of Asia. Ecological and evolutionary factors underlying catadromy include osmoregulatory adaptations, energy optimization, and predation pressure, as well as hydrological connectivity between freshwater and marine systems. Conservation and management often focus on maintaining migratory pathways, mitigating barriers such as dams, and protecting spawning and juvenile habitats, given that disruption of these migrations can impact population viability.