First Published: March 1992, Fishes of Sahul: Volume 7/2
Melanotaenia trifasciata (Wonga Ck)
I've said it before and I'll say it again-one of the best things about native fish collecting, for me, is never knowing what the next stream will bring. The Northern Territory has always been frontier country in most respects and that is still true when it comes to freshwater fish. There are so many areas that have never been surveyed fully if at all and Arnhem Land is probably the least surveyed section.
Our travels took us to the Gove Peninsula and the mining town of Nhulumbuy where a permit from the Northern Land Council allowed us to look at some of the recreational sites that the townspeople enjoyed. The few places we surveyed were all special in their own way and the variety of colour forms we were able to discover in the local fish was astonishing.
Melanotaenia trifasciata, the Banded Rainbowfish, holds a special place in the affection of most collectors of Australian native aquarium fish and its distribution stretches across the top of Northern Australia. However this general range is not continuous and between the presently recorded extremes from Iron Range on the east coast of Cape York Peninsula to the Mary River in the Northern Territory there are large unexplained gaps. For example, south of the Coen River and all around the rest of the Gulf of Carpentaria, M. trifasciata has been strangely absent as far as I can ascertain. There is also a population recorded from Bathurst/Melville Islands north of Darwin. Although it co-exists with several other species of Rainbowfish and inhabits waters of varying hardness and pH, generally trifasciatas are found where the water is moving and relatively clear. Most commonly they congregate in small schools which are constantly searching the surface and mid-waters for insects and crustacea. Associated with these schools are one or more dominant males whose colours are more intense.
As a result of the combined process of studying our maps, talking to the locals and consulting our permit we decided to try to establish whether trifasciatas were present in streams flowing south into the Gulf of Carpentaria. The most permanent-looking was Wonga Creek which flows the opposite way to the Giddy River and empties into Port Bradshaw which is the most northerly inlet on the western coastline of the Gulf. Access is by 4WD track which initially follows the course of the upper Giddy past several huge waterholes eroded into the rocky escarpment. The subsequent crest of the watershed was sandy Wallum country not unlike parts of Fraser Island, even down to a species of Banksia growing beside the track.
An hour or so of steady downhill driving brought us to a lovely campsite where crystal clear water spilled over a shallow rocky cascade into a large pool. We were advised by the campers that this pool was the upper limit of tidal influence and the rest of the creek was navigable by dinghy down to Port Bradshaw (approximately 20 kilometres). They also said fishing there was excellent with Barramundi, Mangrove Jacks and Queenfish plentiful - however so were the crocodiles.
Light was fading as we arrived so we hurried about our tasks. First a couple of photos, then test the water - pH 6.6, hardness minimal, temperature 23 degrees Celsius. The substrate was rocky and slippery underfoot due to algae, while the only aquatic plants seen were an occasional Blyxa and some Nitella. Pandanus and grasses lined the margins while surrounding vegetation included various Eucalypts and the ubiquitous Livistonia palms.
Aside from a few Empire Gudgeons darting around the substrate the visible fish population was all Rainbowfish. Small schools of varying size were obvious but not especially easy to catch in appreciable numbers. The excitement was almost palpable when Dave Wilson pulled out the first big male on his lightweight angling gear and held it up in the afternoon sun. Undoubtedly it was a trifasciata but these fish were as blue as the Goyder River form was red! Spectacular!
No written description can really do them justice but I will try anyway. The shape is classic trifasciata, not slender like Pascoes nor stubby like Goyders tend to be. The central longitudinal stripe is broad and dark purplish-black underlined by a white stripe. The opercular spot is bright red and this colour is repeated in two to three longitudinal lines in the upper half of the body. There are also several dark lines in the lower half of the body. However the outstanding impression of the body colour is a deep purplish-blue with a metallic sheen especially when viewed with front light. Finnage is also spectacular with several parallel zones of rich colours-the outer margin is black then a band of deep blue then a band of red followed by a stripe of lighter blue close to the body. Caudals are clear red. All in all, one hell of a fish!