The Southeast Asian cichlid, Etroplus suratensis, more commonly known as the Green chromide, has made its way to Singapore.
The Green chromide is native to Southern India and Sri Lanka, where it is found in estuaries, brackish lagoons, and offshore coastal waters. The species has been known as an aquarium fish in Europe and North America for decades, but regarded as difficult to keep and even more difficult to breed, perhaps because adults are marine fishes that visit brackish habitats only for short periods, to breed.
In 1995 Etroplus suratensis was found living feral in Singapore, in a national park where rangers regularly monitor the wildlife, so it can be assumed it had not been present for any length of time.
There is no record of the species in any of the published fish surveys performed in Singapore up to December 1993, so it is believed it arrived during the period 1993-1995. It has subsequently been recorded at a number of sites around the island and appears to be thriving.
The source of the introduction is unclear. Green chromides have historically been imported to Singapore for the aquarium trade, so it is possible that specimens could have been dumped or escaped from fish farms. However, in the 1980s the species was introduced to parts of mainland Malaysia as a food fish, and it is thus equally possible that it may have made its own way to Singapore. Interestingly, Singapore Etroplus are now being caught for aquarium shops on the island.
A couple of the sites where the Green chromide is living and breeding are freshwater reservoirs, which it may have entered from the sea when sluices were opened to release excess water. Some of the introductions in Malaysia were also into freshwater reservoirs.
The fact that the species has adapted successfully to these completely freshwater habitats suggests that its purported requirement for salt may be a myth, although equally the process of adaptation may have been a case of the survival of the fittest with heavy losses of those unable to cope with fresh water in the long term.
There is no doubt that Green chromides do better in brackish or marine conditions in the aquarium, so throwing out the salt would be a premature step.
For further details see: Ng, T. H. & H. H. Tan (2010) The introduction, origin and life-history attributes of the non-native cichlid Etroplus suratensis in the coastal waters of Singapore. Journal of Fish Biology 76, 2238–2260.