Ecology and origin of the introduced cichlid Acarichthys heckelii in Singapore's fresh waters-first instance of establishment

The South American cichlid fish, Acarichthys heckelii, is one of many exotic species established in Singapore's artificial freshwater habitat; forming the only recorded population outside its native distribution. The discovery of an A. heckelii individual in a sensitive natural waterway (Nee Soon Swamp Forest) prompted this study, which aimed to investigate the distribution, diet, growth and reproductive ecology of the fish, as well as its possible route of introduction. We found that A. heckelii is largely restricted to artificial freshwater bodies, although a sizable established population occurs in a modified waterway connected to Nee Soon Swamp Forest. Gut contents revealed that the fish fed mainly on benthic algae and macroinvertebrates, the latter occurring in higher frequencies in larger individuals. While unable to ascertain clear seasonality in its breeding, we observed a peak in reproductive investment coinciding with the Northeast monsoon, indicating possible life history adaptations. Genetic comparisons of the cytochrome b mitochondrial marker between individuals from South America, Singapore and the ornamental fish trade shows that the A. heckelii populations in Singapore's fresh waters are more closely related to fishes in the ornamental fish trade than the native population in South America, corroborating anecdotal evidences identifying aquarists as the source of local releases. Our findings also demonstrate the viability of the ornamental trade as an avenue of species introduction and the potential invasiveness of A. heckelii.