River Blackfish

Scientific Name

Gadopsis marmoratus

Other Common Names

Slippery, slimy, blackfish

Size

Up to 600 mm and 5.5 kg, commonly to 300 mm, fish South of the Great Dividing range, especially in South Eastern Victoria often grow to much larger size than their Northern brethren.

Conservation Status

Common

Distribution

Common in rivers and streams South of the Great dividing Range in Victoria and in higher waters in the South Eastern Murray-Darling basin.  Original range extended trhoughout most of Victoria into south-eastern South Australia (the latter group possibly constituting a distinct taxonomic identity) and at elevations above 600-900 in New South Wales and souther Queensland on the western slopes of the Great Dividing Range.

Now much less common with many areas only holding remnant populations if any.  Blackfish are particularly susceptible to siltation in their preferred small upland streams due to their habitat preferences.  Common agricultural practice throughout the Murray Darling basin has consequently severely restricted the distribution of this fish.

Habitat

Associated with instream cover, rock or wood debris areas providing shelter from high water velocities.  Only infrequently encountered in open water or above homogeneous substrates without cover.

History

The size differential between Northern and Southern fish warrants further investigation to determine whether the southern (larger fish) population actually constitute a separate species or sub-species.  Some very preliminary work done recently suggets that this may be the case.

Another outstanding issue is the question of where to place the Gadopsis genus taxanomically.  Some researchers have suggested that this genus, rather than constituting a separate family Gadopidae, should be placed in the family Percichthyidae, the family containing Murray cod amongst others.  This remains controversial, but proponents of the idea point to significant morphological and behavioural similarities between the blackfishes and Murray cod.

Like most things relating to the scientific study of Australian native fish, most of the work required to resolve these and many other issues remains to be done.

Reproduction

In late spring to early summer, eggs laid on bottom surface of hollow log or similar location at various depths in water column.  Male guards eggs and attached larvae.

Diet

Other fish, aquatic insects.  An ambush predator.

Angling

Often overlooked as an angling option, blackfish provide fine sport on light tackle.  In some areas, blackfish can reach truly prodigious size, so heavier gear is required at times.

Blackfish are generally caught using bait, scrubworms being the best option.  Some anglers report success fishing with small, dark coloured lures fished close into creek banks at dusk.  Wet flies have also been used with success.

Remember that blackfish are an ambush predator and are secretive rather than shy.  The trick is to get your bait or lure to within striking distance of the fish which is generally in heavy cover or lurking under an undercut bank.

On the table

A superb eating fish with soft white flesh, blackfish need gentle treatment when cooking for best results.  Fillets from larger fish may be poached of gently fried in a little butter.  Do not over cook.  Smaller fish are probably best cooked whole.