Freshwater Sole

Interesting Info

• The Freshwater Sole is a small flatfish in the tongue sole family (Cynoglossidae) and is found in northern Australia and southern Papua New Guinea.
• They they occur from the Kimberley region (WA), across the Top End (NT), through the Gulf of Carpentaria, and into Cape York (QLD).
• Like other soles, both eyes are on the right side of the head, so they can lie flat and camouflaged against sand or mud.
• Their upper surface is light brown to olive-grey with faint speckles, while the underside is pale. They can even change shade slightly to better blend with their surroundings.
• Unlike most soles that are strictly marine, this species is most often found in freshwater rivers, billabongs, and floodplain lagoons. It also tolerates brackish water, especially in tidal creeks and estuaries.
• They are considered true freshwater soles, capable of living far upstream — surveys have found them in river reaches hundreds of kilometres from the sea.
• Their diet is made up of tiny invertebrates, including worms, insect larvae, and small crustaceans, which they pick from the substrate.
• They remain motionless for long periods, relying on camouflage, before darting forward to snap up prey.
• Breeding happens in the wet season (December–March) when rivers flood. Eggs and larvae are planktonic, drifting downstream before juveniles settle onto the bottom as mini flatfish.
• They are well adapted to northern Australia’s seasonal flood–drought cycle, spreading across floodplains in the wet season and retreating to permanent billabongs and river holes in the dry.
• Lifespan is not well documented, but is estimated at 3–5 years, based on similar-sized flatfish.