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These remarkable images show hundreds of fish (most likely Cox's Gudgeons) climbing the wet, 1.5 m-high side of Penrith Weir in the early 1980s.
The images were taken by freshwater ecologist Dr John Harris, who was working at the time with New South Wales Fisheries.
Cox's Gudgeon isn't the only species of Australian freshwater fish that is known for its ability to climb steep surfaces. The aptly named Climbing Galaxias, Galaxias brevipinnis, can also climb steep wet surfaces. In fact the 'school' of fish in these images could contain Climbing Galaxias.
The Mountain Galaxias, Galaxias olidus, is also a strong climber capable of scaling impressive obstacles. On the page A Tale of Climbing Galaxias, Ranger Ian McArtney relates his observations of Mountain Galaxias climbing Winburndale Dam in 1993.
Perhaps the best known 'climbers' are the freshwater eels that are capable of moving over land for remarkable distances, a feat only equaled by their incredible marine migrations. Learn more about the Longfin Eel.