ON my way to write this column on a warm summer evening in southern Queensland, I walk past a few cane toads on the side of the path to the door to my office. I open the door and upon entering the room I hear the now familiar scurrying of the Asian house gekoes that live inside the air conditioner, covering the wall beneath it with their excrement. And I am here to write about tilapia and peacock bass. What do all of these animals have in common? They should not be here.
In Australia we have done a pretty good job buggering up the natural environment, and indeed we’re up there with the best in the world in that regard when it comes to introducing pests. Early European explorers were not adverse to releasing various plants and animals (as well as ships rats) into new environments, usually as gifts to indigenous peoples, but always with a keen eye towards making the search for food easier next time they visited. But the trend gained momentum after 1788, when European settlers began introducing exotic animals at a great rate.
It began by intentionally settling domesticated animals including pigs, horses, sheep, goats, cattle, rabbits and chickens, as well as various crops and seeds with the first fleet, a necessity for the establishment of the new nation. However, what is less commonly known is that unintentional hitch hikers also arrived on those early ships, including the aforementioned rats and mice, and a variety of fouling organisms on the outsides of the hull that were unceremoniously scraped off and dumped into the various harbours around the country. This is how we managed to score populations of desirables like European flat oysters and mussels, as well as undesirables like pleated sea squirts, ship borers, mud worms and a myriad of other problem invertebrates. Unfortunately, these unintentional early introductions are also thought to have bought in some nasty diseases, some of which may have helped decimate populations of native oysters in later years.
As colonisation continued, a variety of other animals were introduced as part of the efforts of State “acclimatisation societies”, including dogs, cats, foxes, house sparrows, pidgeons, starlings, ducks, geese, and the list goes on. In the piscatorial realm. introductions of trout and salmon were pursued with great zeal, culminating in the establishment of brown trout in Tasmania in the 1860’s from eggs transported on ice for 3-4 months sailing from the UK. Rainbow trout were established a few decades later from the late 1890’s through several introductions from New Zealand. One of the greatest mistakes was the introduction of the cane toad in 1935 from Hawaii by the Bureau of Sugar Experiment Stations scientists in an attempt to control the sugar cane beetle – not our scientist’s finest hour, that’s for sure.
Today due to the volume of international trade, the threat from introduction of exotic pests and diseases has never been greater. Asian house gekoes probably first arrived in Darwin in the 1960’s on containers from Asia, since spreading throughout the country displacing native geckoes as they go. Then there are the various invertebrates and other nasties that arrive through ballast water and biofouling of international shipping, including European shore crabs, the north Pacific seastar introduced into Tasmania and Victoria, the POMS virus devastating aquaculture of Pacific oysters (itself an introduced species) in NSW and Tasmania, and so on.
With all of the threats from ballast water and shipping, and plenty of lessons from the past about inappropriate introductions, we really don’t need any more surprises. But that is exactly what happened earlier this year in the Pioneer River near Mackay, Queensland, where anglers reported catching (and unfortunately releasing – on video!) the exotic peacock bass (Cichla spp.). For sportfishers everywhere, and freshwater addicts in particular, these supercharged, hard fighting cichlids are one of those “bucket list” species that keen anglers dream of. But as anyone who knows even a skerrick about fishes can attest, this is one species that has no place at all in Australian ecosystems.
Northern Australia already has some problems from other cichlids, namely Tilapias that have been introduced into the wild from aquarium fishes taken from their native Africa. In contrast, peacock bass are cichlids that originate from South America, also probably bought into Australia as ornamental fishes a while back. It seems some bright spark, possibly an aquarium fish breeder who is also a keen fisher, decided it would be a great idea to try to establish a population of these fish in the waters above Dumbelton Weir on the Pioneer River. We can assume this person knew it was a very illegal thing to (with large penalties if they were ever caught), but what this person apparently did not know (or did not care), is that peacock bass are top level predators known to cause significant ecological damage when they are introduced into new systems. Like the Asian house gecko, (and unlike tilapia) peacock bass are highly likely to displace native fishes by increasing predation pressure as well as directly competing with iconic sportfish such as barramundi and mangrove jacks for food and space. Then there are the exotic disease risks that are rife throughout the aquarium fish industry. If given a choice between barra, other natives like sooty grunter and a feral fish from South America, any true blue Australian angler would choose the natives, surely?
Peacock bass are the largest of the cichlids, with over 15 different species known to science, some of them growing to nearly a meter long. From the photos of the fish taken below Dumbelton Weir it looked like it was one of the larger species, possibly C. monoculus or C. temensis (giant peacock bass, growing to 90+ cm and over 12 kg), or a hybrid thereof. However, closer examination is needed for genetic analysis, but initial efforts by Queensland Fisheries to obtain samples by electrofishing and gill netting were unsuccessful, so the species remains unknown for now and it appears the population size is small at this time. The fish which was photographed was definitely an adult based on its size, possibly a female due to the drab colour (sexes in peacock bass are easily identified by the fact that male fish are more brightly coloured, and with maturity develop a prominent frontal hump on the head). Each spawning period, females deposit a relatively small number (thousands) of sticky eggs on a convenient substrate (often a flat stone in shallow water) before brooding the larvae in their mouths once the eggs hatch (just like Tilapia). The mouth brooding strategy of the peacock bass vastly improves the survival rates of the young fish, contributing to the ability of this species to outcompete native fishes wherever they have been introduced into suitable new locations.
As the lessons with Tilapia show, once a pest fish like peacock bass become established in large, open waterways it can be very difficult to eradicate them. Anglers that catch or spot Peacock Bass in the Pioneer River or elsewhere must report it to the Department of Agriculture and Fisheries (DAF) QLD by emailing photos to pestfish@daf.qld.gov.au or calling 13 25 23, ensuring you have the details of where the fish was encountered. DAF’s advice is, if caught, anglers should not return any peacock bass to the water, or they risk large fines. Rather, they are asked to kill the fish humanely (brain location information for peacock bass is available at www.ikijime.com) and dispose of it properly, which in this case is in your freezer while you alert the DAF hotline of where to pick up their samples.
