Kākahi - freshwater mussels

Pānui Taiao - July 2021

Many people don’t realise that New Zealand has 3 endemic species of kākahi (freshwater mussels).

Kākahi are different from marine mussels in that they don’t attach themselves to rocks, instead moving around on river beds using their ‘foot’.

They also have an unusual life cycle. Unlike marine mussels, female kākahi have a brood chamber where they grow juvenile kākahi – these are called glochidia and are very small, about the size of a grain of sand.

When an unsuspecting host fish swims too close, the mother kākahi sneezes the glochidia onto the fish, where they attach themselves with little hooks and spent part of their life cycle living in its gills or fins as parasites. Eventually the glochidia fall off onto the river bed below and grow into adult kākahi.

Kākahi are a valued mahinga kai species and traditionally held many uses. Although they’re not known for tasting very good, they don’t move far which once made them a secure food supply, especially during winter. Kākahi can be kept alive for weeks in a damp kete, which makes them a good food to travel with, and they can also be preserved by drying.

The shells were used for rattles on kites, to scrape flax into muka fibre to weave with, and to cut things with including hair and umbilical cords. Kākahi were sometimes traditionally used to feed young children when mothers and wet nurses were not available.

Kākahi were considered to be so useful and important that there was a proverb among some iwi:

Tane moe whare, kurua te takataka; tane rou kakahi, aitia te ure

Man drowsing in the house, smack his head; man skilled in dredging kākahi, marry him

Kākahi improve the environment as they filter water while they are filter feeding. New Zealand’s species are the most efficient filterers in the world, able to filter one litre of water per hour. This improves the water quality and makes the habitat better for everything living nearby.

Kākahi populations are declining, and there are many possible reasons for this including loss of habitat, pests, pollution and declining populations of the host fish they need to complete their life cycle.

If you're interested in looking for kākahi in a waterway, the best places to start are in the shallower, slower flowing water on the edges of the river. Kākahi like living in finer sediment such as fine gravel, sand, silt and mud.

They are often found in undercut banks – the best way to look for them there is to put your hand underneath and feel around in the silt and mud – and hope that no tuna is living there!

If you know of any kākahi populations around the district, please let our biosecurity team know so we can monitor them for our data.