SUTTON LANDCARE 12 AUGUST 2014
Freshwater Fish of the Canberra Region:
their ecology, current threats and future threats.
On Tuesday 12 August 2014, Associate Professor Mark Lintermans from the University of
Canberra, addressed the meeting. He is a freshwater scientist and a national authority on
threatened freshwater fish, His address focussed on the distribution and ecology of
freshwater fish in the upper Murrumbidgee catchment. He highlighted the major threats to
these freshwater fish, and what can be done to assist the recovery of freshwater habitats in
our region.
His wide-ranging presentation included the following points:
• Firstly setting the scene, around half of the world’s vertebrates are fish. There are around
32,000 fish species and half of these are freshwater fish.
• Australia has only about 250 freshwater fish species. This is mostly because Australia is
such a dry continent, has little run-off, and has been geographically isolated for many
centuries.
• 77% of Australia’s freshwater fish species are widespread; however diversity decreases
from north to south, with distance from the sea, and with altitude.
• The Murray Darling Basin has only 47 freshwater fish species, 36 native and 11 alien. 23
of the 36 native fish species are considered threatened.
• Freshwater fish have five basic needs:
1. Ability to move (to cater for variable spawning times, food and refuge shortages, larval
dispersion). Radio-tagging reveals that Murray Cod might move 120km/year. By contrast
some Blackfish only move 15m in their whole lifetime. Macquarie Perch are very mobile at
night.
2. Favourable conditions for reproduction (spawning variables include temperature and light).
3. Food. Fish tend to be either surface feeders, mid-depth feeders or bottom feeders. Many
freshwater fish just eat riparian vegetation
4. Shelter. Threats include in-stream predators, aerial predators, fast flows, lack of shade,
rocks as landmarks, and lack of fringe vegetation.
5. Suitable water quality. Problems include black water (high in decaying organic matter),
endocrine disruptors (such as sewage), cold water (from dams), salinity, and algal blooms.
• Native freshwater fish in our region include: Murray Cod, Macquarie Perch, Silver Perch,
Blackfish, Australian Smelt, Western Carp Gudgeon (a species of cod), Dwarf Flathead
Gudgeon, Trout Cod, Common Galaxia and other Galaxia such as Tantangara Galaxia which
was first identified in 2011. Many Galaxia species are critically endangered, not least
because they make great trout food. It is illegal to fish for some species (eg. trout cod).
• Alien (ie. introduced) freshwater fish in our region include: Carp, Redfin Perch, Rainbow
Trout, Brown Trout, Gambrusia (aka mosquito fish – but they don’t eat mosquitoes), Oriental
Weather Loach, and Goldfish (carp-like but don’t have whiskers). The last three mentioned
are often chosen for aquarium fish.
• Alien species in our region were uncommon until the 1960s but following their
introduction (deliberate or accidental) they have caused problems. Some species carry
viruses, many compete aggressively for food, and some eat fish eggs of native fish.
• Some alien species (particularly trout) were deliberately introduced to provide stock for
anglers. Recreational fishing for some species (particularly Murray Cod) is strictly controlled.
• Threats to native freshwater fish include (in addition to those mentioned above):
1. Habitat destruction (removing snags, straightening waterways, pollution by ash from fires).
2. Barriers (large dams can cause a drop in water temperature of up to 10°C, leading to slower
fish growth rates and the threat of missing temperature-related spawning cues).
3. Translocation and stocking of competing species.
4. River regulations (too many dams, too much irrigation pumping, fewer flow peaks and
actual reversal of seasonal flow patterns).
5. Politics (saltwater and freshwater fisheries are controlled by different Govt agencies).
• Fish restocking. A political subject. Around 79 million “infant fish” introduced locally in
the decade 2000-2010, in part to support recreational angling. Conservation stocking has been
quite minor. Stocked fish tend to be naive and easy prey for predators. Fish numbers are not a
good indicator of river health (because of the huge restocking factor). Data indicates that,
in some locations, recreational fishing can take more fish than commercial fishing.
• How can we help?
1. Riparian fencing and plantings (provides shade, destocking, cleaner water and slower
flows. Dense plantings of willows and poplars can be problematic because they drop their
leaves all at once.)
2. Don’t construct weirs (they restrict fish movement upstream)
3. Don’t fill gullies with rubbish
4. Control erosion and limit sediment entering waterways.
5. Retain dead trees in streams or on the banks (they provide shelter/shade and flow control)
6. Take care with pumping out of streams (particularly in droughts and for building estates)
7. Don’t release unwanted aquarium fish into streams (a significant ongoing problem)
8. Don’t use live fish as bait. (it is illegal to use trout as bait in NSW).
From questions arising from the floor:
• Stocking farm dams with fish – water needs to be 3-5m deep (for temperature stability).
Trout and perch will grow but are unlikely to breed. They will eat any yabbies nearby (but
on the upside they will eat leeches too). Our region is a bit warm for trout. Farm dams are
too small for freshwater crayfish (there are some in the Murrumbidgee River, but none in the
Yass River).
• Tilapia are second only to salmon as a popular farm-raised fish world-wide. They are easy
to maintain and are a good source of dietary protein. However they are very predatory so
need very careful management. Tilapia are listed as noxious in NSW and possession and sale
of live tilapia is prohibited.
• Tilapia and the (native) Mouth Almighty are unusual. They carry their fertilised fish eggs
in their mouth until they hatch. (Alien) Gambrusia practice internal fertilisation.
This summary certainly does not cover everything that Professor Mark Lintermans mentioned.
It is a shame that more people were not there to benefit from his comprehensive presentation.