25 September, 2008

Tilapia Terrorises the Tropics

Tilapia Terrorises the Tropics
In north Queensland we have two introduced Tilapia species. This one, Oreochromis mossambicus, Mozambique tilapia, was photographed yesterday in the Freshwater Lake at Centenary Lakes, Flecker Botanic Gardens, Cairns.

It, along with many other males have established breeding areas which they have cleaned. they have adopted their colourful breeding condition to impress the females. See the red margins to the dorsal and caudal fins, the bright red pectoral fins and the pale yellow cheek patch on the gill covers. the females are smaller, more grey and with less prominent lips. Young are pale grey with a spot on the posterior margin of the dorsal fin.

Tilapia eat detritus, live plants and prey on the eggs and fry of other fish. They can live in a wide range of habitats and reach incredible densities. They are tough fish being able to withstand unusual pH levels and low oxygen as well as high salinity and fresh water conditions. When those in the water features of a golf course in Port Douglas were killed using a fish poison something like thirteen tonnes of fish bodies had to be disposed of. These fish pose a threat to prawn and barramundi stocks and hence people's livelihoods. The beautiful endangered Oxleyan Pygmy Perch, Nannoperca oxleyana, and the vulnerable Honey Blue-eye, Pseudomugil mellis, are under threat from the expansion of this species range.

The dumping of exotic fish in our streams and lakes has made Australia one of the world's hot spots for fish invasions. Native fish and crustacea are also being spread into areas where they did not occur with the loss of local species being the result. Lake Eacham no longer has Lake Eacham Rainbow Fish. There used to be millions. When I first moved to the Atherton Tablelands I would sit on a log in the Lake and these little fish would suck on the hairs of my legs until the tickling got too much for me. Some of these introductions are by misguided people releasing aquarium specimens but others are done by people who want to fish for the species they are introducing. It is a shame that such environmental vandalism is still occurring; Tilapia have been found recently in the Walsh River Catchment and near Cooktown.

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