Jack Dempsey cichlids (Cichlasoma octofasciatum) are an aggressive freshwater fish named after the heavyweight boxer Jack Dempsey. They are a medium-sized fish native to Central America and can be distinguished from other cichlids by the presence of two grey-black bars on the top of their head, which extend forward between their eyes. Their background colour is dark blue and they have a series of white to iridescent blue spots on their fins, head and body, and a series of dark bars along their sides.
A population of Jack Dempsey cichlids was discovered in a pool on the NSW north coast in 2004. A concerted effort to eradicate this population was made in 2004/05, but was unsuccessful. This highlights the importance of preventing such species from entering our waterways as it is very difficult and sometimes impossible to eliminate pest fish once they become established in the wild.
Jack Dempsey cichlids are a member of the Cichlidae family, and are native to Central America. In Australia, they are a popular aquarium fish typically sold for tropical freshwater tanks, although their aggressive nature means they are not suitable for community tanks. They can live more than 10 years and can reach 25 cm in length. They prefer temperatures of between 22 and 30oC, but can survive in temperatures as low as 8-10oC. They cannot tolerate very high salinities (up to 8 ppt, much less than seawater).
Jack Dempsey cichlids feed opportunistically on a range of organisms including insects, worms, crayfish, molluscs, small fish and filamentous algae. In the wild they are found in swampy areas with warm, murky water. Females lay approximately 500-800 eggs per clutch onto the substrate. The eggs are protected by both parents, which are extremely aggressive towards other fish during the spawning season.
A population of Jack Dempsey cichlids was found in early 2004 in the Angourie area, near Yamba on the NSW north coast. This population is confined to an isolated flooded quarry locally known as the ‘Green Pool’. There are no other known populations of the Jack Dempsey cichlid in the wild in NSW.
Jack Dempsey cichlids are popular aquarium fish and there is little doubt that this feral population has established from discarded aquarium fish. Because the pool where Jack Dempseys occur is not connected to other waterways, it is unlikely they could spread further without human assistance or a large flood.
It is illegal to release fish into the wild without a stocking permit and heavy penalties apply. The release of small aquarium fish can cause significant damage to our native fish and other wildlife. NSW DPI recommends unwanted fish are given to a friend or pet shop. If an appropriate home cannot be found see the recommended guidelines for humane destruction of fish.
When Jack Dempseys were first discovered in the Green Pool, Angourie they were considered an ideal target to attempt a pest fish eradication program, because the pool was relatively small, confined, and contained few native fish. However there were also some limits on what methods could be used because the pool is a popular local swimming location. After considering the options available it was decided to trial explosives – a novel technique that had been used with some success in Western Australia.
Three eradication attempts, using lines of detonation cord laid out across the pool’s surface by a qualified explosives expert, were carried out between September 2004 and June 2005 (several successive attempts were necessary as eggs and larvae are not killed by the shock wave). After the use of explosives, 36 large Australian bass were released into the pool to help prey on any remaining larvae or juveniles.
Unfortunately, follow up monitoring by the department has found Jack Dempseys still remain in the pool. It is possible that the fish are very hardy and some survived the blasts, or alternatively they may have been deliberately re-introduced.
NSW DPI is not planning any further eradication work at this time.
Many of the most popular cichlids for aquariums are easy to keep because they are hardy, adaptable and breed prolifically. Unfortunately, such features also make them likely to survive, establish and become pests if released into the wild.
Several other cichlid species, including the Mozambique mouthbrooder (Oreochromis mossambicus), black mangrove cichlid (Tilapia mariae) and pearl eartheater (Geophagus brasiliensis) have become established in various locations around Australia with the pearl eartheater being discovered in 2009 in northern NSW, in pools below Clarie Hall Dam, on a tributary of the Tweed River.
There is often little information on how these species impact native fish and habitats, although many are capable of dominating native fish populations through their aggressive behaviour and competition for food and space. The particularly aggressive temperament of the Jack Dempsey cichlid raises further concerns about the threat this fish would pose to native fauna if it were to establish in other NSW waterways.