Life cycle of freshwater mussels
Freshwater mussels have an unusual life cycle. They can live from about 10 to 40 years. Females brood eggs in modified sections of the gills, called marsupia, where they develop into bivalved larvae, called glochidia, bearing a pair of hooks on the apex of each shell valve. Most species brood in spring and summer.
The glochidium is parasitic and must attach to the gills or fins of a fish to complete its development. Female mussels produce large numbers of glochidia but few find a fish host and even fewer survive to maturity. Species of Hyridella produce tens of thousands of glochidia in each brooding cycle and may breed repeatedly during the warmer months. In contrast, Cucumerunio novaehollandiae produces millions of glochidia but reproduces only once per season.
A wide range of native fish species including smelt, gudgeons and Australian bass are used as hosts, as well as some introduced species, including the eastern gambusia. Goldfish and common carp are not suitable hosts. This inter-dependence between mussels and fish means that the wellbeing of mussel communities is closely linked to the health of the resident fish community.
After detaching from their hosts, juvenile mussels burrow into the stream bed where they grow rapidly for a few years.
A glochidium larva of Hyridella depressa is about a quarter of a millimetre in diameter and, to the naked eye, looks like a grain of sand.
Photo: M. Byrne.
A glochidium of the mussel Hyridella drapeta attached to the gill rakers of an Australian smelt.
Photo: Hugh Jones, OEH
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Page last updated: 03 February 2014