Header: Male Tilapia. Photos by Gunther Schmida
Being a keen sherman and having a passion for the environment, the issue of pest fish is very close to my heart. Tilapia is one of the most common and destructive pest fish in South East Queensland (SEQ), having taken up residence in many of our local waterways and reservoirs.
Growing to a maximum length of 40 cm, tilapia fiis one of the toughest and most resilient fish species in our waterways. They can survive in temperatures from 80C to 420C, preferring still or slow moving water in a variety of habitats, including reservoirs, lakes, ponds, rivers, creeks, drains, swamps and even tidal creeks and estuaries. To my surprise and also disappointment, my first encounter with a tilapia was in Townsville in a saltwater creek, 50 metres from the ocean and with views of Magnetic Island.
There are two species of tilapia that have escaped into the wild in Queensland: Mozambique Tilapia (Oreochromis mossambicus) and Spotted Tilapia (Tilapia mariae). Of the two, O. mossambicus is the most common and the main one found in SEQ. Generally, most O. mossambicus are olive to yellow in colour on the dorsal area, with silvery sides and a whitish belly – although breeding males are much darker, with red tips on their fins. Being part of the Cichlidae family, they were a sought after aquarium fish but also were irresponsibly released into local waterways.
One of the first recorded sightings of tilapia within SEQ was in Tingalpa Reservoir in 1977. Since then, populations have been recorded in Maroochy, North Pine, South Pine, Caboolture, Brisbane, Bremer, Logan, Stanley and Albert Rivers, as well as connected creeks and drainages throughout the Gold Coast, Brisbane and Deception Bay.
Pine, Wivenhoe, Somerset, Maroon and Moogerah Dams and also Lake Kurwongbah. Unfortunately due the recent flooding of most of our major waterways, tilapia have now spread to many more dams, waterholes, creeks and rivers. As many Land for Wildlife properties adjoin or contain waterways, it is likely that tilapia could now exist within a water body on your property.
Male tilapia build circular breeding nests in clusters of sand or muddy riverbeds. These nests should not be confused with the native Eel-tailed Cat fish, Tandanus tandanus (pages 4-5), which build fewer, larger nests often in gravelly riverbeds and are religiously patrol. Tilapia are mouth- brooders, meaning, once deposited in nests, females hold their eggs (100-1700 per female) for 3-5 days and larvae for 10- 15 days in their mouth until they are big enough to survive most predators. For this reason, populations can explode quickly, as unlike most other native fish species, their survival rate is very high.
The impacts of tilapia are widespread and include environmental issues such as decreased water quality, introduction of disease, competition for resources, predation of native fish and economic and recreational impacts such as reduced value of conservation areas and decreasing the catch of recreational and commercial sherman. These impacts are why tilapia are declared noxious in Queensland under the Fisheries Act 1994 (Fisheries Regulation 2008). It is unlawful to have noxious fish (alive or dead) in your possession, or to use them as bait, and it is illegal to place or release noxious fish (alive or dead) into Queensland waterways. Penalties of up to $200,000 may apply.
Although the presence of pest fish can potentially have devastating results, it is important to know that they often come hand-in-hand with already degraded waterways. Regulation of waterway flow, fish barriers, pesticide runoff , exotic weeds, over exploitation of fish stocks and removal of bankside vegetation are all threats to the health of a waterway, potentially increasing the risk of a noxious fish population. Revegetating riparian areas, as well as stabilising banks and creating in-stream habitat will improve the overall health of the waterway and competition for noxious fish.
Even though tilapia are noxious fish they can still be targeted to reduce numbers. By law, they have to be humanely disposed of and placed well above the high watermark, immediately after capture. This is in case a female with a brood of eggs in its mouth is caught, since these eggs can be viable for up to a day out of water. Simple fishing methods, using bread or prawns as bait, can be used to catch tilapia. They are a fun and safe fish for children to catch and are a good way to educate people of the affects that pest species have on the natural environment.
It has proven extremely difficult and expensive to eradicate pest fish once they have become established in the wild.
Therefore, it is vital to prevent noxious pests such as tilapia from entering or spreading further throughout our waterways. Governments are trying to stop the spread of tilapia and other noxious fish through an education and identification program. An easy way to distinguish a pest fish from a native fish is that the majority of pest fish have a continuous dorsal fin, while native fish have a dent or gap separating the front of the dorsal fin from the rear.
If you suspect you have tilapia or any other noxious fish in a waterway on your property, report sightings to the Department of Employment, Economic Development and Innovation (DEEDI) Customer Service Centre by phoning 13 25 23, emailing [email protected] or filling out the Pest Fish Reporting Form online at www. fisheries.qld.gov.au. The State Government has a fact sheet on how to identify and report sightings of tilapia, which can be accessed through http:// tinyurl.com/kpkuvft
Article by Cody Hochen Land for Wildlife Officer Brisbane City Council
References and Further Reading
Allen GR, Midgley SH & Allen M (2002) Field Guide to the Freshwater Fishes of Australia. Western Australian Museum.
Queensland Museum (2007) Freshwater Fishes of Greater Brisbane Region – A Queensland Museum Wild Guide. Queensland Museum.
Queensland Museum (2007) Wildlife of Greater Brisbane. Queensland Museum.