Australian Grayling

Australian Grayling

This is a small, native freshwater fish (adults 16-25cm long) which looks similar to a herring. Its most distinguishing feature is its strong "cucumber smell" when alive and freshly dead. It was considered extinct in Victoria pre 1970 because the population once abundant in the Yarra River (and fished by anglers) appeared to have died out.

The start of wide-ranging fish surveys by the Fisheries and Wildlife Department in the early 1970's found good numbers of grayling first in the Combienbar River in Gippsland, then in almost all coastal waters west of the Hopkins River. Very large populations were found in the Mitchell, Tambo and Barwon Rivers. Surveys revealed that they still occurred in the lower Yarra River and should now recolonise upstream since a fishway has been constructed at Dight's Falls.

Details of their biology, population structure, feeding etc are known from several studies of the populations particularly in the Tambo River. However most details about their spawning sites and spawning behaviour are still unknown. Eggs were hatched out in fresh water in Tasmania in 1886 suggesting that spawning may occur in fresh water rather than the estuaries but no further studies were carried out until the mid 1980's when ripe, spawning and spent fish were collected from the upper reaches of the Mitchell and other rivers. Further experiments were also carried out on hatching eggs in the laboratory. It is now generally accepted that the fish spawn in fresh water during periods of higher flow in April/May.

The remainder of their early life history is still a mystery despite attempts to capture fry or very small juveniles in several rivers in Victoria, Tasmania and New South Wales. Grayling smaller than 50mm have not been captured in fresh water and young grayling less than about 45mm length have not been found in typical estuarine localities. It is believed that the eggs are laid in gravel on the substrate in freshwater rivers. The hatched larvae (which are slender, buoyant and attracted to light) swim to the surface and are swept downstream to the estuaries. Here they develop and grow, eventually swimming back upstream into freshwater habitats where they spend the remainder of their lives.