River blackfish

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River blackfish

Least Concern  (IUCN 3.1)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Family: Percichthyidae
Genus: Gadopsis
Species:
G. marmoratus
Binomial name
Gadopsis marmoratus

The river blackfish (Gadopsis marmoratus) is a freshwater fish endemic to the temperate waters of south-eastern

lowland habitats as well. Originally, river blackfish co-inhabited many of its lowland and "midland" habitats with species such as Murray cod and golden perch, and its upland habitats with species such as trout cod and Macquarie perch. It is a popular angling fish in some parts of its range.[2]

Description

River blackfish are elongated with a rounded body, distinct snout and large mouth, and small to moderate sized eyes. The

anal fin
are rounded. The spiny dorsal fin is low, weak and blends into the soft dorsal fin. Colour varies but is usually either yellow or green with dark green mottling, or a very dark purple/black colour.

It is an ambush predator that takes crayfish, shrimp, small fish and aquatic insects.[2] It is strongly nocturnal.

Murray-Darling river blackfish show a maximum size of around 30 cm and < 0.8 kg, with larger specimens from coastal drainages reaching up to 60 cm (Gellibrand River).

It is a highly underrated sportsfish, particularly the Southern form (see below). It is fast and strong, and has been shown to take flies and lures, even surface lures, in addition to the more usual worm baits. There is an unofficial world record caught by Piotr Pomorski on a WildBait Lure, in Victoria Australia that measured 70 cm in length.

Range and classification

Victoria. These fish are now often referred to as southern river blackfish. This population shows a far great maximum size of 60 cm or more and about 5.5 kg (12 lb). Specimens this large were likely to be very old — 30 years or more — and are rarely seen now. Southern river blackfish may be a separate species.[citation needed
] The taxonomy does not yet reflect to this.

River blackfish continue the trend present in Murray-Darling native fish of speciating into primarily

Victoria, southeast New South Wales, and the Australian Capital Territory
. While the split may be between lowland (or midland) and upland, there are overlaps in their range, and river blackfish are found in many upland habitats. There are also indications river blackfish populations in the southern and northern halves of the Murray-Darling river system may represent two distinct species or sub-species, with genetic and other differences.

The

Percichthyidae. A mitochondrial DNA study has confirmed a relationship between the Blackfish and the Percichthyidae but the exact relationship was not resolved in that study.[3] Further study is needed to resolve the relationship between the blackfish and the Percichthyidae. In addition, molecular studies have supported the view that G. marmoratus is a species complex of five different species, these include a species in the Murray-Darling Basin and four species in coastal freshwaters.[1] One of these forms from Victoria has been named as Gadopsis gracilis.[4]

Blackfish have a recruitment method similar to Murray cod, but with more specialisation to upland habitats. Blackfish spawn in spring and lay a very limited number of large, adhesive eggs (<1000) on sunken timber (

snags
), or in the case of two-spined blackfish on submerged rocks. Similar to Murray cod, the male guards the eggs until they hatch. Upon hatching the larval blackfish are, uniquely, attached to their ruptured egg case by a tether until the yolk sac is largely used and the larvae are ready to commence exogenous feeding. (This unique structure is presumably an adaptation to upland river/stream habitats, to prevent larvae being swept away in currents.)

Conservation

Blackfish have declined very seriously due to overfishing, stream siltation and snag removal, and predation and competition by introduced species, particularly introduced trout species. Recent bushfires in south-eastern Australia (2003–2006) have filled many blackfish rivers with large quantities of silt, and infilled the interstices ("gaps") between larger rocks that blackfish normally use as a refuge from predatory alien trout species. The presumed result will be increased levels of alien trout predation on blackfish, and the long-term future of blackfish species 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.

River Blackfish are a protected species in South Australia.[2]

References

  1. ^
    doi:10.2305/IUCN.UK.2019-3.RLTS.T123358463A123382771.en
    . Retrieved 20 November 2021.
  2. ^ a b c d Bray, Dianne. "River Blackfish, Gadopsis marmoratus". Fishes of Australia. Retrieved 3 September 2014.
  3. PMID 11277628
    .
  4. ^ Eschmeyer, William N.; Fricke, Ron & van der Laan, Richard (eds.). "Species in the genus Gadopsis". Catalog of Fishes. California Academy of Sciences. Retrieved 13 May 2020.
  • "Gadopsis marmoratus". Integrated Taxonomic Information System. Retrieved 19 March 2006.
  • Froese, Rainer; Pauly, Daniel (eds.) (2005). "Gadopsis marmoratus" in FishBase. 10 2005 version.
  • Jackson, P. D. (1978). "Spawning and early development of the River Blackfish", Gadopsis marmoratus Richardson (Gadopsiformes: Gadopsidae) in the McKenzie River, Victoria. Australian Journal of Marine and Freshwater Research 29: 293–298.
  • Jerry, D.R., Elphinstone, M.S and Baverstock, P.R. (2001). "Phylogenetic Relationships of Australian Members of the Family Percichthyidae Inferred from Mitochondrial 12S rRNA Sequence Data". Molecular Phylogenetics and Evolution 18: 335–347.

External links

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