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.
• Follow the ethical euthanasia code in Euthanasia of animals used for scientific purposes (PDF, 1.8MB).
• 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 category 3, 5, 6 and 7 restricted noxious fish under the Biosecurity Act 2014. You must not:

• keep it
• feed it
• give it away
• sell it
• release it into the environment.

If you do any of these, penalties may apply.

You must take all reasonable and practical measures that are under your control to minimise the biosecurity risks associated with dealing with tilapia. This is part of your general biosecurity obligation.