ASFB Home > 2003 > Biological Invasions: Consequences for Parasites, Pathogens, Emerging Diseases, and Fisheries in the Marine Environment.

Addition of artificial hollow refuge in an agricultural stream: Does river blackfish (Gadopsis marmoratus Richardson) utilise them?

Minal T Khan, Tariq A Khan and Michael E Wilson

Centre for Environmental Management, University of Ballarat, P O Box 663, Ballarat 3353, Victoria, Australia.
Email: m.khan@ballarat.edu.au

Population of River blackfish (Gadopsis marmoratus Richardson) appears patchy, with fish common in some streams and absent from nearby ones. Information that correlates habitat limitation to the size or structure of river blackfish populations is scant. River blackfish are said to be dependent on hollows in submerged wood for spawning; yet fish can be abundant in agricultural zones with heavily modified riparian vegetation. To explore if hollows were limiting, we added 15 hollows to each of three pools with known river blackfish population in a multiple-BACI design. The study stream was Birch Creek in western Victoria in the headwaters of the Loddon River and hollows were placed prior to the breeding season. Size class distribution of river blackfish in the six experimental pools (three with added hollows and three controls) was broad, suggesting that recruitment was regularly occurring. All pools had at least 8 fish of >15 cm which were assumed to be of breeding age. Despite considerable movement between refuges within pools, very few hollows were occupied as daytime refuges by river blackfish. As newly placed hollows were not immediately utilised for spawning we concluded that either spawning occurred but hollows were not a limiting factor or that spawning failed to occur in any location tested.

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