Retropinna is a genus of small, silvery, freshwater and estuarine fish belonging to the family Retropinnidae, commonly referred to as southern smelts. Species within this genus are native to the temperate regions of Australia and New Zealand, where they inhabit slow‑moving rivers, lakes, and coastal lagoons.
Taxonomy
- Kingdom: Animalia
- Phylum: Chordata
- Class: Actinopterygii
- Order: Osmeriformes
- Family: Retropinnidae
- Genus: Retropinna Whitley, 1948
Recognized Species
The genus currently comprises two valid species:
- Retropinna retropinna (J. Richardson, 1849) – commonly known as the New Zealand smelt.
- Retropinna lineata (Günther, 1867) – commonly known as the Australian smelt.
Distribution and Habitat
R. retropinna is endemic to New Zealand and occurs throughout both the North and South Islands, primarily in lowland streams, lakes, and brackish estuaries. R. lineata is found in southeastern Australia, including Tasmania, where it occupies similar freshwater and estuarine environments. Both species show a tolerance for a range of water temperatures and can thrive in habitats with moderate vegetation and sandy or silty substrates.
Morphology
Members of Retropinna are elongated, laterally compressed fish typically measuring 5–12 cm in total length. They possess a silvery‑grey coloration with a translucent, laterally placed eye and a single dorsal fin situated mid‑body. The anal fin mirrors the dorsal fin in size and position. The family Retropinnidae is characterized by the presence of a small adipose fin and a forked caudal fin.
Ecology and Life History
Retropinna species are omnivorous, feeding on planktonic crustaceans, insect larvae, and small fish eggs. They exhibit diel vertical migrations, often moving into shallower waters at night to feed. Reproduction occurs in spring and early summer; females lay adhesive eggs on submerged vegetation or gravel, and the larvae are pelagic before transitioning to benthic habitats. Growth rates are relatively rapid, with individuals reaching sexual maturity within one year.
Conservation Status
Both R. retropinna and R. lineata are classified as “Least Concern” by the International Union for Conservation of Nature (IUCN), owing to their broad distribution and stable population trends. However, localized threats such as habitat modification, water extraction, and invasive species may affect specific populations.
Human Interactions
Species of Retropinna are occasionally targeted by recreational anglers and are also utilized in some regions for bait. Their small size limits commercial fisheries interest, but they play a role in the food web as prey for larger piscivorous fishes, birds, and mammals.
References
- Nelson, J. S. (2006). Fishes of the World (4th ed.). John Wiley & Sons.
- McDowall, R. M. (1990). Freshwater Fishes of New Zealand. New Zealand Department of Conservation.
- IUCN Red List of Threatened Species. (2022). Retropinna species assessments.
