Tilapia

O. mossambicus

• Grows to more than 36cm.
• Lives up to 13 years.
• Usually dark grey or almost black but can be silver with 2–5 dark blotches/spots on the side.
• Breeding males can have red tips on their fins.
• Deep-bodied with a thin profile and long pointed fins.

T. mariae

• Ranges from dark olive-green to light yellow.
• 8 or 9 dark bars or blotches on the sides (obvious in younger fish).
• Grows to 30cm.
• Deep-bodied with a thin profile and long pointed fins.

O. mossambicus

• Hardy fish, can survive temperatures between 8 and 42°C.
• Requires temperatures of about 16°C to remain active and feed.
• Can withstand high-saline waters and low-dissolved oxygen.

T. mariae

• Less tolerant of cooler temperatures and therefore found at lower latitudes.

• Established in Queensland.

Breeding

• Sexually mature at 3 years or less in favourable conditions.
• O. mossambicus can become sexually mature at small sizes in poor conditions, or during times of overcrowding. Known as 'stunting', this results in large populations of mature fish with small bodies.
• O. mossambicus are mouthbrooders. Females protect eggs and small fry from predators by holding them in their mouths. Males build large circular breeding nests in soft silt or muddy layers.
• T. mariae lay their eggs on hard surfaces.

Diet

• Diet is omnivorous.
• O. mossambicus feed mainly on plankton, insects and weed but will take a wide variety of other foods.
• T. mariae mainly eat plants.

Environmental

• Successfully invades and dominates many water habitats due to their high ability to reproduce and survive in very different conditions, and simple food needs.
• Can rapidly outnumber native fish and dominate aquatic communities.
• Can survive environments where native fish find coping difficult.
• Unlike many native freshwater fish, tilapia can retreat downstream into highly saline waters during drought and move back upstream when conditions improve.
• Affects native species as they compete for habitat and food, behave aggressively and disturb plant beds when building nests.

Social

• Loss of favourite fishing locations due to tilapia invading and destroying native fish populations. Tilapia can create large, monospecific (single species) fisheries.

How they are spread

• Most new infestations are caused by human-assisted translocation (movement of live fish). This includes private dam stocking and moving tilapia between catchments to use as bait, or to create new 'fisheries'.
• Biosecurity Queensland maintains a strict 'no-take' approach to manage tilapia and reduce the spread of this noxious fish.

Monitoring and action

• If you catch tilapia in the wild, humanely kill them and do not return them to the water. If you see or catch tilapia outside of their known distribution, take a photo and report it online or phone Biosecurity Queensland on 13 25 23.
• Follow the ethical euthanasia code in Euthanasia of animals used for scientific purposes (PDF, 1.8MB), the 2001 Australian & New Zealand Council for the Care of Animals in Research and Teaching publication. The most appropriate way may be to stun the fish with a sharp blow to the back of the head, just above the eyes. When done correctly, this causes brain destruction—the fish's gill covers should stop moving and eyes should remain still.
• Intensive fishing may reduce pest fish numbers in small enclosed waterbodies, but this practice alone is not an effective long-term control strategy.

Poisoning

• Poisons can completely remove pest fish in ponds and small dams, but are not practical for rivers and streams as these poisons also kill native fish.

• Tilapia is a restricted noxious fish under the Biosecurity Act 2014.
• You must not keep, feed, give away, sell, or release tilapia into the environment.
• If you catch these species, you must immediately humanely kill and dispose of them by burying them above the high-water mark or disposing of them in a nearby bin.
• By law, you have a general biosecurity obligation (GBO) to take reasonable and practical steps to minimise the risks associated with restricted noxious fish under your control.