amphidromous

Amphidromous is a term used in ichthyology to describe a diadromous life-history pattern in which individuals migrate between freshwater and marine environments at different life stages, but not specifically for the purpose of breeding. In typical amphidromous fishes, eggs hatch in freshwater, the larvae are carried to the sea or an estuary to develop, and juveniles migrate back into rivers or streams to grow to maturity. The adults may reside in freshwater or brackish habitats, and reproduction is not tied to a particular migratory phase.

This pattern contrasts with other diadromous strategies. In anadromy, adults spend most of their lives in seawater and migrate to freshwater to spawn, while in catadromy, adults reside in freshwater and migrate to the sea to spawn. Amphidromy is characterized by larval dispersal between habitats as part of the normal life cycle, rather than a migration that directly accompanies reproduction.

Ecology and distribution vary by species, but amphidromous taxa commonly inhabit coastal streams, estuaries, and nearby marine environments. Examples include certain gobies (family Gobiidae) and some mullets (family Mugilidae). The life-history strategy can be sensitive to environmental changes such as damming, water pollution, and habitat fragmentation, which may disrupt larval transport or juvenile recruitment.

As a life-history term, amphidromy describes a migration pattern and is not a taxonomic grouping. Knowledge of amphidromous species informs studies of population connectivity, habitat requirement, and conservation planning in freshwater-marine interfaces.