Torrentfish

Torrentfish

Cheimarrichthys fosteri (von Haast, 1874)

This little fish is the only freshwater member of the Cheimarrichthyidae family in New Zealand. Closely related to the more familiar blue cod, the scientific name of this fish means literally torrent (cheimarros) fish (ichthyos). And it’s an apt name for this species because that is exactly where this fish lives - right in the swift white rapids of stony rivers and streams. The flattened head and large pectoral fins help this fish to anchor on the riverbed, while the raised eyes and ventral mouth are probably adaptations for feeding in this habitat. These later two features, along with the distinct dark bands along the sides, easily distinguish the torrentfish from other freshwater species.

Despite its skill at living in swift water, the torrentfish is not a good climber and only penetrates inland in river systems where the gradient is relatively low.  It is less common in Otago and Southland than in other parts of New Zealand, and torrentfish have never been reported from Fiordland, Stewart, or Chatham Islands. It is not found in any other country except New Zealand.

Like many of New Zealand’s freshwater fish, the torrentfish undertakes migrations between the sea and fresh water as part of its life cycle. Looking just like tiny replicas of the adults, juvenile torrentfish enter fresh water in spring and autumn, and after a few weeks in the estuaries, begin moving upstream to the adult habitat. The adults continue to move slowly upstream, with the largest and most inland fish being the females and those in the lower reaches predominately males. How and where they get together for spawning is unknown - we suspect the females move downstream to the males, but no spawning sites or spawning behaviour has ever been observed. Despite the mystery surrounding aspects of its life cycle, torrentfish are one of the most common fish in open-bedded rivers in New Zealand.