The distribution, biology and ecological impacts of three introduced freshwater Teleosts in Western Australia

The distribution, biology and ecological impacts of three introduced freshwater teleosts in Western Australia were investigated. The One-Spot Livebearer (Phalloceros caudimaculatus: Poeciliidae), the Swordtail (Xiphophorus helleri: Poeciliidae) and Tilapia or Mozambique Mouthbrooder (Oreochromis mossambicus: Cichlidae), are popular ornamental species that exist in selfsustaining feral populations in the Indian Ocean (Pilbara) or the Southwest Coast Drainage divisions of Western Australia. Phalloceros caudimaculatus is a small (females up to 60, males up to 40 mm TL), non-aggressive, sexually dimorphic poeciliid native to central South America that has existed as a feral species in Western Australia for at least 30 years. A total of 9697 specimens were collected in 12 samples from 2 populations (Bull Creek and Lesmurdie Brook) in metropolitan Perth between September 2002 and April 2003. Dietary and reproductive analyses were conducted on three seasonal samples, i.e. spring, summer and autumn. The diets of individuals in both populations were significantly different though both consisted primarily of vegetal matter and silt/biofilm. Mean total fecundity, size at maturity, and lengths and weights of pregnant fish were lower in fish from Bull Creek, than in those from Lesmurdie Brook. The possible causes of the different observed life history strategies (i.e. reproductive and growth strategies) in both locations are discussed, with temperature considered to be the primary causative factor. A literature review and the results of tank trials with native species determined P. caudimaculatus to be a peaceful species that did not demonstrate the agonistic traits of Gambusia holbrooki. Due to this fact, and the primarily vegetal/detrital diet of P. caudimaculatus, it is proposed that the species may have a lesser impact on native fishes than G. holbrooki. It is also proposed that P. caudimaculatus has displaced G. holbrooki in lentic and lotic systems due to its longer breeding period and greater tolerance to cold temperatures and increased water flow. Xiphophorus helleri is a moderately small (females and males up to at least 70 mm), sexually dimorphic poeciliid native to central and northern South America, that was recently (i.e. 1999) discovered in the Irwin River in the Indian Ocean Drainage Division. A total of 324 specimens were collected between September 2002 and April 2003. Dietary and reproductive analyses were conducted on three seasonal samples, i.e. spring, summer and autumn. The diets of individuals consisted primarily of vegetal matter and silt/biofilm. Mean total fecundity was lower than reported in the literature, i.e. ca 36 compared with ca 60. Oreochromis mossambicus is a large (up to 400 mm TL), aggressive cichlid native to tropical eastern Africa that has existed as a feral species in Western Australia for at least 20 years. A total of 7099 specimens of 0. mossambicus and sympatric species were collected in 3 seasonal samples (spring, summer and autumn) from 2 locations (Gascoyne River and Chapman River) in the Indian Ocean Drainage Division between September 2002 and April 2003. In the Gascoyne River, small (less than 53 mm) 0. mossambicus consumed principally aquatic fauna, while large (greater than 165 mm) 0. mossambicus consumed vegetal matter and silt/biofilm. The diets of 0. mossambicus were significantly different to the sympatric species M cephalus, L. unicolor and H. compressa. Only small (less than 63 mm) 0. mossambicus were collected from the Chapman River. These consumed principally filamentous and unicellular algae. The diets of 0. mossambicus were significantly different to the sympatric species M cephalus, A. butcheri, A. caudavittata, P. olorum, G. holbrooki and H. compressa. In the Gascoyne River, male 0. mossambicus displayed agonistic behaviour towards sympatric species and each other during the extended breeding period.