An adult Two-spined blackfish with “giraffe-like” patterning
By Ben Broadhurst
Institute for Applied Ecology, University of Canberra
My favourite freshwater fish species would have to be the Two-spined blackfish or “blackies” as they are known to those who work on them (I’ve studied them for over a decade, so we are on a nickname basis). The Two-spined blackfish is a medium sized member of the Percichthyidae family (freshwater basses and cods) endemic to the Murray-Darling Basin in south-eastern Australia. This species primarily inhabits cool upland rivers and streams where it prefers shelter provided by spaces between cobbles and boulders. This species grows to a maximum of around 350 mm total length, though individuals over 250 mm are uncommon. This species is usually abundant where it is present though has a highly disconnected distribution with many populations now fragmented from each other. This species is highly susceptible to sedimentation and is a common prey item of alien trout species.
Typical Two-spined blackfish habitat, a cobble / boulder-bottomed upland stream (Photo: Ben Broadhurst)
Two-spined blackfish are a highly charismatic freshwater fish, manoeuvring largely with their pectoral fins in and out of structure, much like clown fishes do in anemones on coral reefs. An outstanding feature of the Two-spined blackfish is their marbled, almost giraffe-like, patterning of dark greens and yellows, more prevalent in some individuals than others. During some aquaria-based trials we have conducted on radio-tag retention of Two-spined blackfish, my colleagues and I noted that they became tame and boisterous very quickly and would feed from the hand within a week or so of being captured. Whilst snorkelling in rivers where this species is present, I’ve found them to be quite inquisitive, with my presence acknowledged; but they usually do not attempt to escape or take shelter.
Two-spined blackfish spawn in late-spring to early summer. Although natural egg locations are difficult to locate, it is hypothesised that this species deposits it sticky eggs onto a hard, sediment free surface. After spawning the male take responsibility for guarding and fanning the eggs (and larvae) to keep them oxygenated and free from sediment. Some experimental studies have had success with spawning Two-spined blackfish in PVC tubes.
I’ve had the pleasure of studying the movement patterns of this species using radio-telemetry in both riverine and reservoir environments. My research has shown that this species is nocturnally active and returns back to its home rock or piece of timber each morning after foraging on aquatic insects throughout the night. In rivers, Two-spined blackfish generally exhibit small home ranges of around 15 – 30 m, generally completing a day’s movements within the same pool. In reservoirs, Two-spined blackfish can move more than 500 m in a night, moving to feeding grounds at dusk then returning to their daytime shelters at dawn.
An Adult two-spined blackfish being gently anaesthetized prior to radio-tag insertion
Koehn, J. D. (1990). Distribution and conservation status of the two-spined blackfish Gadopsis bispinosus in Victoria. Proceedings of the Royal Society of Victoria 102, 97-103.
Jackson, P. D., Koehn, J. D., Lintermans, M. & Sanger, A. C. (1996). Family Gadopsidae: Freshwater blackfishes. In Freshwater fishes of south-eastern Australia (McDowall, R. M., ed.), pp. 186-190. Australia: Reed Books.
Lintermans, M. (1998). The ecology of the two-spined blackfish Gadopsis bispinosus (Pisces: Gadopsidae). Unpublished M. Sc. Thesis. p. 219. Canberra: School of Botany and Zoology, Australian National University.
O’Connor, J. P. & Zampatti, B. P. (2006). Spawning season and site location of Gadopsis bispinosus Sanger (Pisces: Gadopsidae) in a montane stream of southeastern Australia. Transactions of the Royal Society of South Australia 130, 227-232.
Broadhurst, B. T., Lintermans, M., Thiem, J. D., Ebner, B. C., Wright, D. W. & Clear, R. C. (2012). Spatial ecology and habitat use of two-spined blackfish Gadopsis bispinosus in an upland reservoir. Aquatic Ecology 46, 297-309.
Broadhurst, B., Dyer, J., Ebner, B., Thiem, J. & Pridmore, P. (2011). Response of two-spined blackfish Gadopsis bispinosus to short-term flow fluctuations in an upland Australian stream. Hydrobiologia 673, 63-77.
Ben Broadhurst is a scientist at the University of Canberra. He specialises in studying the ecology of inland freshwater fishes and is a keen angler.