The torrentfish, or panoko (Māori), is an amphidromous freshwater fish that is endemic to New Zealand. Torrentfish are well adapted to life in shallow, fast-flowing riffles and rapids. They grow to a maximum of 20 cm (7.9 in) in total length, but more commonly reach 10–12 cm (3.9–4.7 in).

Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres. Such migrations are usually done for better feeding or to reproduce, but in other cases the reasons are unclear.