Betta brace yourselves…
No, it’s not a spelling mistake. The wetlands of the Northern Territory of Australia are in big trouble.
And it’s all because of this small fish, the Siamese fighting fish (Betta splendens). Native to Southeast Asia and living in wetlands and small streams, this is one of the toughest fish of all, and some complete idiot released them into the Adelaide River system near Fogg Dam, possibly either as mosquito control (which native fish such as rainbowfish and blue-eyes do very well at anyway) or because they wanted to get rid of unwanted aquarium fish. Either way, it was three years ago that I was out at Fogg dam with friend Richard, and he asked what kind of fish it was lying on its side in some shallow water. I couldn’t believe what I was seeing, so I collected it and took some pictures before handing it in to Fisheries who were very interested. That fish is pictured above and is the very first record of this species (and likely ANY introduced species) making it successfully into the NT. Fast forward to now, and the damn things are everywhere in the lower Adelaide system. I got a call from Dr Michael Hammer from the NT Museum and Art Gallery who had found hundreds of them migrating at a small weir at Fogg Dam a week or two ago after someone had turned one in. In Beatrice Creek they outnumber natives in one spot (at least). Some have suggested that they are no threat. This is rubbish:
- They are in plague proportions already, meaning that they are displacing natives and are successfully competing for food resources
- They are aggressive to other fish. Although supposed to only attack their own kind I observed one rip the legs off a tadpole, killing it. Rainbow fish and anything coming near the heavily guarded nests will be attacked for sure
- It is suggested they will be washed out of the swamps, which they may, but this species has a very strong upstream urge and will rapidly colonise any swamp they can reach
- They can wriggle over land in the tiniest trickles of water and survive zero oxygen in the water, breathing through a special “labyrinth organ” which acts like a lung
- Mosquitoes are already controlled by native fish, when they can reach them. As many mozzies will breed in temporary puddles well out of reach of even fighting fish, the mosquito population is unlikely to suffer
In short, this looks to be the new cane toad of the swamps, a fish at least as problematic as the mosquito fish (Gambusia) which has caused untold damage to native frogs and fish in the south. The NT enjoyed not having any feral populations of noxious fish… until now.
So please, NEVER release aquarium fish into the wild. Give them back to the pet shop or a friend. “Saving” your unwanted fish is likely to kill millions more.