thumb|left|250px|Striped eel catfish, [[Plotosus lineatus]]
The eeltail catfish are a family (Plotosidae) of catfish whose tails are elongated in an eel-like fashion. These catfishes are native to the Indian Ocean and western Pacific from Japan to Australia and Fiji. The family includes about 41 species in 10 genera. About half of the species are freshwater, occurring in Australia and New Guinea.
Unlike most marine teleosts, eeltails have an extra-branchial salt-secreting dendritic organ for osmoregulation. The dendritic organ is likely a product of convergent evolution with other vertebrate salt-secreting organs. The role of this organ was discovered by its high NKA and NKCC activity in response to increasing salinity. However, the Plotosidae dendritic organ may be of limited use under extreme salinity conditions, compared to more typical gill-based ionoregulation.