Formosan landlocked salmon

What it is

This fish is a subspecies of masu salmon with a dark green back and silver belly. Adults grow up to 57 cm long and display nine elliptical dark spots on their sides. During mating season, males develop a red hue on their flanks and an upturned jaw. The fins are separated, with the dorsal fin clearly divided into anterior and posterior sections. Its body is covered in cycloid scales, and it lacks a basibranchial tooth. The head features a green top with silver around the eyes and a distinct dark spot on the operculum.

Where it lives

It lives exclusively in the upper reaches of the Tachia River system in Taiwan. Specific habitats include the Chichiawan and Kaoshan streams within Shei-Pa National Park. These alpine valleys sit above 1,500 metres elevation where water temperatures stay below 17 °C. The fish prefers plunge pools and backwaters formed by natural dams. Canopy cover from riparian forests keeps the water cool and reduces sediment runoff. Substrate changes from boulders in summer to pebbles and cobbles in winter.

How it lives

Aquatic insects such as caddisflies, mayflies, and stoneflies form the bulk of its diet. In dry seasons, it shifts to eating predatory aquatic insects. Larger individuals also consume terrestrial prey more frequently than smaller fish. The species is largely sedentary in summer but moves short distances to feed. Habitat selection varies by season, with adults seeking deeper, faster water in warm months. In winter, they move to shallower areas with slower currents. Riparian vegetation supports the food web by feeding the insects the salmon eat.

Breeding and life cycle

Spawning occurs in the second half of October when water temperatures drop to 11–15 °C. Two-year-old females dominate the breeding population. They use their tails to clear silt and build oval gravel nests. Eggs develop for 20 to 30 days and hatch in late November. Sexual maturity is reached before two years of age. Growth in size and biomass happens early in the life cycle. The average lifespan ranges from four to five years.

Fish and people

The Atayal people traditionally called this fish bunban or n'bang and used it as food. The Japanese government designated it a national treasure in 1938, introducing fishing bans. These protections ended in 1945, leading to a sharp population decline. Commercial fishing is now banned, though subsistence and sport fishing occur. The fish holds cultural value in Taiwan. Artificial propagation programmes began in the 1980s to help restore numbers after habitat degradation from agriculture and dams reduced the wild population severely.

Status and threats

Listed as Critically Endangered, this is one of the rarest fish globally. Habitat loss from farming, pollution, and climate change threatens its survival. Genetic diversity has dropped due to small population sizes. Counts fell to 200 individuals in 1992 but rose to over 15,000 by 2023 thanks to conservation work. The Shei-Pa National Park Administration monitors the population closely. Continued protection of upstream watersheds is vital as rising temperatures threaten their cold-water habitat.

Relatives and look-alikes

It belongs to the cherry salmon complex and is closely related to the nominate masu salmon. Some taxonomists classify it as a distinct species, while others view it as a subspecies. It shares traits with other landlocked salmonids like the Mexican golden trout. Morphological differences are minimal, requiring genetic tests for accurate identification. It is the southernmost distributed member of the salmon family in Asia.

Questions people ask about Formosan landlocked salmon

Good reading and sources

• Oncorhynchus masou formosanus on WikipediaEncyclopedia
• More photos on Wikimedia CommonsPhotos
• Wikidata recordOpen data