Kākahi – freshwater mussels

Kākahi (also known as torewai or kāeo), or freshwater mussels, are amazing creatures. They are a taonga species to Māori and are a vital element within Aotearoa New Zealand’s freshwater ecosystems. They are found in a range of freshwater habitats, from streams to lakes, and are important filter feeders, with each mussel able to filter a litre of water per hour.

Kākahi have a strong foot that they use to “walk”, burrow into sediment, and anchor themselves. It’s often possible to see the tracks of their wanderings on the lake or streambed. A valued mahinga kai species, they were a reliable source of food for Māori – especially in winter – as they don’t move very far.

Their extraordinary lifecycle is dependent on native fish – for part of their life they are fish parasites. Female kākahi keep their microscopic eggs in a gill pouch, where they are fertilised by a male, then develop into larvae called glochidia. The female releases the glochidia when a fish swims nearby. Kōaro, smelt and bullies are key fish hosts for juvenile kākahi. The glochidia hook onto the fins or gills of the fish where they grow into juveniles then detach from their host. This part of their life cycle is still mysterious, but it’s thought the tiny juveniles drift through water and live below the sediment surface until they reach adulthood. At about four years of age they are able to reproduce. Their average life span is 12-30 years, but these fantastic creatures can live as long as 50 or 60 years.

Kākahi face a number of threats including habitat loss, predation by introduced mammals, pollution, and declining fish host populations that are needed to complete their lifecycle.

Kākahi facts

Three species of kākahi live in different regions of Aotearoa:

Echyridella aucklandica – Threatened – Nationally Vulnerable, present in Te Taitokerau
Echyridella menziesii – At Risk – Declining, present in Te Taitokerau
Echyridella onekaka – At Risk – Naturally Uncommon, not known in Te Taitokerau
Echyridella aucklandica and E. menziesii are sometimes found in the same location
Life span of 12-30 years, sometimes as long as 50 years
Often found in undercut banks