It is thought that Oreochromis mossambicus (Mozambique mouth-brooder) was introduced from Singapore or Indonesia in the 1970s as an aquarium fish. Tilapia mariae (black mangrove cichlid) has been recorded in Victoria, ACT and Queensland.

Queensland

O. mossambicus:

was released into ornamental ponds and subsequently established large populations in the Townsville and Cairns regions by the late 1970s
was first recorded in south-east Queensland in 1977 and Townsville in 1978
was first reported in far north Queensland in 1986, from near Leslie Creek (Upper Barron River). There were no further reports until 1995, when tilapia were also found in Kenny Creek (Upper Barron River).
had a self-maintaining population in Leslie Harrison Dam, Tingalpa in 1979. By 1980, tilapia had spread to Tingalpa Creek. They were found in North Pine Dam in 1981.
has two distinct genetic strains found in Queensland a common southern strain found in Brisbane and Townsville, and a northern strain found only in the Cairns area.

It is unknown when and where T. mariae was first introduced.

Distribution in Queensland

O. mossambicus

	North Queensland	Brisbane
Unconfirmed populations	Ross River estuary and above Aplin weir, Woolcock Street stormwater drain, an artificial lake development upstream of Woolcock Street drains, Louisa Creek, Rowes Bay drainage system, Rowes Bay, Healey Creek system, Bohle River, Kewarra Beach to Palm Cove, the Barron River, Port Douglas, the lower Mulgrave River, the lower North and South Johnstone Rivers and coastal waterways and estuaries around Cairns	Tingalpa Reservoir, Tingalpa Creek, North Pine Dam, North Pine River, South Pine River, Dowes Lagoon (Sandgate), Wivenhoe Dam, Somerset Dam, Kilcoy Creek and other feeder creeks to Somerset Dam, Kedron Brook, Forest Lake
Confirmed populations	Townsville Common, Yeppoon area and the Burdekin River	Lake Kurwongbah, farm dams in the North Pine Dam area. Two specimens were caught near Toowoomba but it is uncertain whether a population has become established.

T. mariae

T. mariae is found in the Cairns region, the Lower Barron River and its tributaries, Freshwater Creek and also in the Johnstone River (probably due to movement by humans, not natural spread). It has moved into Trinity Inlet streams and Thomatis Creek and is present in the Mulgrave and Russell Rivers. There are also reports of T. mariae in Leslie Creek.

Potential for spread

Breeding populations of O. mossambicus in tropical and subtropical Queensland are cause for concern due to their rapid growth, short maturation time (3-12 months), high rate of reproduction and wide temperature tolerance. There is considerable potential for northerly spread, but low potential for southerly spread due to intolerance of tilapia for low temperatures. There is potential for tilapia to spread west into the Gulf of Carpentaria.

Natural spread is very slow. However, there is high potential for spread due to movement by humans or via human-created routes such as pipelines and irrigation channels.

Biology

O. mossambicus:

has pale olive to silver-grey bodies with two to five dark blotches on the side. Breeding males become almost black with red edging on their fins.
can be up to 40 cm long but is able to reach sexual maturity at small sizes in poor environmental conditions (stunting).

T. mariae:

has vertical stripes on the head and body and vary in colour from dark olive-green to light-yellowish green. The stripes are less distinct in larger fish.

Due to the different breeding strategies of O. mossambicus and T. mariae, it is highly unlikely that they could ever hybridise in the wild.

Reproduction

O. mossambicus:

is a mouth-brooder (a means of reproduction in which a large number of the young survive)
builds nests and males may be aggressive when defending nests during the breeding season
can produce up to 1200 eggs/year. Fry (baby fish) are released in shallow waters by females once they have reached lengths of 9-10 mm.
produces a large number of young in food-rich environments, and can produce large numbers of small, reproductively mature ('stunted') individuals when overcrowded
breeds between September/October and April/May in Queensland, with up to four broods per year.

T. mariae:

is not a mouth-brooder and usually attaches its eggs to hard surfaces. It does not build nests but does look after the young.
spawn between September and March.

Environmental tolerances

O. mossambicus is able to withstand a wide range of temperatures (8-42°C), but requires temperatures of approximately 16°C to remain active and feed, and higher temperatures to breed (>20-24°C). They also have wide physiological tolerances they can withstand high salinities (0-120 g/L) and low dissolved oxygen (0.1 mg/L) and can survive, grow and even reproduce in seawater.

T. mariae is also able to withstand a wide range of salinites (euryhaline) and temperatures (eurythermal) although they are less tolerant of cooler temperatures and therefore have a narrower latitudinal range than O. mossambicus.

Habitat preferences

O. mossambicus has colonised a variety of habitats within Australia and now occur and often breeds in large artificial reservoirs, ornamental ponds and riverine habitats (including artificial drainage channels, pools and backwaters), tidally flushed creeks and small freshwater creeks.

Movement

O. mossambicus

is sedentary and disperses slowly, even in flood-prone areas
has been slow to disperse in Queensland. It has taken nearly 20 years for it to disperse from the point of introduction to virtually all waterways in the Townsville-Thuringowa region.

T. mariae also became established in the Cairns region during the past 20 years.

Feeding habits

O. mossambicus feeds on zooplankton, insects and weed.

T. mariae are classified as opportunistic herbivores, although there is evidence that they eat animals when aquatic vegetation is limited.

Effect on environment

Current

O. mossambicus lives with Australian native species although they are sometimes able to survive in conditions that are too degraded for native fishes.

Tilapia appear to have become the dominant species in many areas, although little is known about how they affect native fish and habitats. There is anecdotal evidence that tilapia are avoided by predators if native fish are available, although they have been found in barramundi guts.

Potential

It is difficult to assess the potential effects of tilapia on Australian native species and aquatic habitats, as very little research has been done.

Tilapia probably have an effect on native species via competition for habitat and food resources and complex predator-prey relationships.
There may also be potential effects from introduced diseases and parasites.
There is anecdotal evidence that O. mossambicus disturb aquatic plant beds when building nests.
Tilapia may affect native fishes through their aggressive behaviour.

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Student resource i.2 Introductory

Priority species: Tilapia (all species of the genera Oreochromis, Tilapia and Sarotherodon)

History of introduction

Australia

Queensland

Distribution in Queensland

Potential for spread

Biology

Reproduction

Environmental tolerances

Habitat preferences

Movement

Feeding habits

Effect on environment

Current

Potential

Student resource i.2
Introductory