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Poorohe (Common Smelt)

A widespread and ecologically important native fish of Aotearoa New Zealand

Overview of Poorohe

Poorohe, also known as the common smelt (Retropinna retropinna), is a small native fish found throughout Aotearoa New Zealand. They typically grow between 60 and 100 millimetres in length and have slender, translucent, silver-grey bodies with a faint greenish sheen along the back.

Their streamlined shape and reflective colouring allow them to blend into open water and avoid predators. Poorohe are commonly found in rivers, lakes, wetlands, estuaries, and harbours, making them one of New Zealand's most adaptable native fish species.

Habitat and Distribution

Poorohe inhabit both freshwater and coastal environments, often forming large schools in slow-flowing rivers, lake margins, and estuarine waters. They tolerate a wide range of temperatures and salinities, allowing them to move freely between freshwater and marine systems.

Juveniles are especially common in estuaries and harbours, which provide rich feeding grounds and shelter from strong river flows.

Life Cycle

The life cycle of Retropinna retropinna varies depending on habitat. Some populations are entirely freshwater, while others are diadromous, migrating between rivers and the sea.

01
Spawning

Spawning usually occurs in spring and early summer when adults release their eggs in slow-flowing streams, lake margins, or estuarine shallows.

02
Egg Development

The fertilised eggs settle among vegetation and sediment, hatching into larvae that drift with currents before developing into juveniles.

03
Maturity

Growth is rapid, and most poorohe reach maturity within their first year of life.

Morphology and Diet
Physical Adaptations

Morphologically, poorohe are well adapted for mid-water swimming. They have soft fins, a forked tail for fast movement, and large eyes for detecting predators and prey.

Feeding Behaviour

Their diet consists mainly of zooplankton, small insects, and aquatic invertebrates, which they capture while swimming in open water. Because of their small size and schooling behaviour, poorohe are an important prey species for many larger fish.

Ecological Importance

Ecologically, Retropinna retropinna play a crucial role in freshwater and estuarine food webs. They form a key link between plankton and higher predators such as trout, kōkopu, eels, birds, and marine fish.

Plankton

Microscopic organisms

Poorohe

Energy transfer

Larger Predators

Trout, eels, birds

By transferring energy from microscopic organisms to larger animals, poorohe help support the overall productivity of aquatic ecosystems. Their abundance often reflects good water quality and healthy habitat connectivity.

Environmental Pressures

Despite their wide distribution, poorohe face several environmental pressures.

Habitat Modification

Habitat modification through river channelisation, wetland drainage, and dam construction reduces available spawning and nursery areas.

Pollution

Pollution from sediment and nutrient runoff can degrade water quality and affect plankton communities that poorohe rely on for food.

Introduced Species

Predation and competition from introduced species, particularly trout and perch, also place pressure on local populations.

Climate Change Impacts
Conclusion

In conclusion, poorohe (Retropinna retropinna) are a widespread and ecologically important native fish in New Zealand. Their role as a key prey species and their ability to link freshwater and estuarine ecosystems make them vital to aquatic food webs.

Protecting waterways, restoring wetlands, and maintaining good water quality are essential to ensure the continued health of poorohe populations across Aotearoa.