Two-spined blackfish
Encyclopedia
The two-spined blackfish, Gadopsis bispinosus, is an Australia
n native freshwater fish. It is a speciated, more specialised upland variant of the river blackfish
, Gadopsis marmoratus.
It is found in the cool, clear, strong-flowing, cobble bottomed, sub-alpine rivers and streams (ranging from small to large) in the southeast corner of the Murray
-Darling
river system. Their range encompasses northeast Victoria
, southeast New South Wales
and the Australian Capital Territory
. Originally two-spined blackfish co-inhabited many of these waters with Macquarie perch
and trout cod
.
Two-spined blackfish are similar in shape and appearance to river blackfish, though their spiny dorsal fin
usually contain only two spines (hence their scientific name) in comparison to river blackfish which have 7 to 13 distinguishable spines in their spiny dorsal fin. (In reality, this is a rather academic point as two-spined blackfish have blurred the difference between the dorsal spines and the dorsal rays that make up their soft dorsal fin, and any distinctions between the two weakly calcified dorsal spines and the dorsal rays that follow it are hard to pick in a living specimen.)
It is much the same as the river blackfish in spawning and diet, however rocks and the interstices ("gaps") between them replace timber as the main spawning and habitat sites for two-spined blackfish, and two-spined blackfish are much smaller, commonly 15 to 17 cm and a maximum size of 25 cm.
Two-spined blackfish have declined seriously due to stream siltation and competition by introduced species, particularly introduced trout species. The species suffers serious predation and competition from introduced species of trout
but due its nocturnal habits and cryptic, cover-oriented behaviour it appears to survive in sufficient numbers to maintain populations in high quality habitats. Recent severe bushfires in south-eastern Australia (2003–2006) however have filled many upland rivers with large quantities of silt, and infilled the interstices ("gaps") between larger rocks that two-spined blackfish normally use as a refuge from predatory trout species. The presumed result will be increased levels of trout predation on two-spined blackfish and the long term future of two-spined blackfish is now of some concern. The blackfish species are very low in fecundity, slow-growing and long lived, and have low migratory tendencies, so are extremely vulnerable to overfishing and localised extinctions.
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n native freshwater fish. It is a speciated, more specialised upland variant of the river blackfish
River Blackfish
The river blackfish, is an Australian native freshwater fish of the Murray-Darling river system, found from southern Queensland through to central Victoria. It is also found in some eastern and southern flowing coastal rivers...
, Gadopsis marmoratus.
It is found in the cool, clear, strong-flowing, cobble bottomed, sub-alpine rivers and streams (ranging from small to large) in the southeast corner of the Murray
Murray River
The Murray River is Australia's longest river. At in length, the Murray rises in the Australian Alps, draining the western side of Australia's highest mountains and, for most of its length, meanders across Australia's inland plains, forming the border between New South Wales and Victoria as it...
-Darling
Darling River
The Darling River is the third longest river in Australia, measuring from its source in northern New South Wales to its confluence with the Murray River at Wentworth, New South Wales. Including its longest contiguous tributaries it is long, making it the longest river system in Australia.The...
river system. Their range encompasses northeast Victoria
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....
, southeast New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
and the Australian Capital Territory
Australian Capital Territory
The Australian Capital Territory, often abbreviated ACT, is the capital territory of the Commonwealth of Australia and is the smallest self-governing internal territory...
. Originally two-spined blackfish co-inhabited many of these waters with Macquarie perch
Macquarie perch
The Macquarie perch is an Australian native freshwater fish of the Murray-Darling river system. It is a member of the Percichthyidae family and is closely related to the golden perch ....
and trout cod
Trout Cod
The trout cod or bluenose cod, Maccullochella macquariensis, is a large predatory freshwater fish of the Maccullochella genus and the Percichthyidae family which was originally found in the south-east corner of the Murray-Darling river system in Australia...
.
Two-spined blackfish are similar in shape and appearance to river blackfish, though their spiny dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
usually contain only two spines (hence their scientific name) in comparison to river blackfish which have 7 to 13 distinguishable spines in their spiny dorsal fin. (In reality, this is a rather academic point as two-spined blackfish have blurred the difference between the dorsal spines and the dorsal rays that make up their soft dorsal fin, and any distinctions between the two weakly calcified dorsal spines and the dorsal rays that follow it are hard to pick in a living specimen.)
It is much the same as the river blackfish in spawning and diet, however rocks and the interstices ("gaps") between them replace timber as the main spawning and habitat sites for two-spined blackfish, and two-spined blackfish are much smaller, commonly 15 to 17 cm and a maximum size of 25 cm.
Two-spined blackfish have declined seriously due to stream siltation and competition by introduced species, particularly introduced trout species. The species suffers serious predation and competition from introduced species of trout
Trout
Trout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...
but due its nocturnal habits and cryptic, cover-oriented behaviour it appears to survive in sufficient numbers to maintain populations in high quality habitats. Recent severe bushfires in south-eastern Australia (2003–2006) however have filled many upland rivers with large quantities of silt, and infilled the interstices ("gaps") between larger rocks that two-spined blackfish normally use as a refuge from predatory trout species. The presumed result will be increased levels of trout predation on two-spined blackfish and the long term future of two-spined blackfish is now of some concern. The blackfish species are very low in fecundity, slow-growing and long lived, and have low migratory tendencies, so are extremely vulnerable to overfishing and localised extinctions.