The two-spined blackfish (''Gadopsis bispinosus'') is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

temperate perch Percichthyidae, the temperate perches, are a family of freshwater ray-finned fish found in Australia and southern South America. Formerly placed in the order Perciformes, they are now placed in the order Centrarchiformes. The name Percichthyida ...

endemic to

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. 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 New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

and the

Australian Capital Territory The Australian Capital Territory (ACT), known as the Federal Capital Territory until 1938, is an internal States and territories of Australia, territory of Australia. Canberra, the capital city of Australia, is situated within the territory, an ...

. 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 A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

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.) The two-spined blackfish is similar to the river blackfish in spawning and diet; however, they prefer rocks and the interstices ("gaps") between to timber as the main spawning and habitat sites. Two-spined blackfish are also much smaller, commonly 15 to 17 cm and a maximum size of 30 cm. The species feeds mostly on aquatic insect larvae and terrestrial invertebrates, and occasionally other fishes and crayfish. Two-spined blackfish breed between October and December. Larvae hatch after around 16 days and remain at the spawning site with the male parent for another 3 weeks. 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 a generic common name for numerous species of carnivorous freshwater ray-finned fishes belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of which are members of the subfamily Salmoninae in the ...

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 Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing Fish stocks, fish stock), resu ...

and localised extinctions.

References

External links

Native Fish Australia - Two-Spined Blackfish page
{{Authority control two-spined blackfish Freshwater fish of Australia two-spined blackfish