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ABSTRACT1. The swordtail Xiphophorus hellerii is a popular ornamental freshwater fish that occurs as an introduced species in the aquatic habitats of at least 31 countries. Although introduced populations are found in other Australian states, the only known Western Australian population occurs in the Irwin River (29115 0 S). 2. The biology of X. hellerii in the Irwin River in south-western Australia is described from four seasonal samples, collected by seine net, between spring 2002 and winter 2003.3. Pregnant females were collected in all seasonal samples, though juveniles were absent in spring, implying that juvenile mortality during late winter is high. Although mean length of pregnant females (38.7 mm) and mean gonadosomatic index (GSI) (14.7) were similar to reported data for X. hellerii populations in Queensland, mean fecundity was markedly lower in Western Australia, i.e. 34.1, cf. 60.15.4. Logistic analysis of the percentage of female and male X. hellerii with developing and mature gonads predicted that the length at which 50% of the sexes mature was 30.8 and 31.5 mm SL, respectively. The sex ratios of females to males did not differ statistically from a ratio of 2:1.5. The diet of all X. hellerii size classes was omnivorous (primarily vegetal matter/algae), although a significant difference was observed between the diet of juveniles and that of the two larger size classes (i.e. juveniles consumed greater quantities of aquatic invertebrates).6. A melanic polymorphism (i.e. pigmented caudal peduncle and fin) was observed in approximately 5% of X. hellerii collected.7. If released, the range of X. hellerii is likely to expand in anthropogenically modified habitats in tropical and temperate latitudes of Western Australia. Potential ecological impacts on indigenous fishes may be magnified owing to the depauperate nature of the endemic ichthyofauna including a lack of predators.

This datasheet on Xiphophorus maculatus covers Identity, Overview, Distribution, Dispersal, Diagnosis, Biology & Ecology, Environmental Requirements, Impacts, Uses, Prevention/Control, Further Information.

The gobiid, Acentrogobius pflaumii, was recorded in Cockburn Sound in southwestern Australia in 2004, and is now reported for the first time from the Swan River Estuary ca. 20 km north of the initial collection site. It was observed by SCUBA divers on open, soft/silt substrata and was abundant in areas of the middle Swan River Estuary. Ballast water emissions from a nearby international port, containing eggs and/or fish, are considered the most likely introductory vector. Although the ichthyofauna of the Swan River Estuary has been frequently surveyed, it is difficult to speculate how long A. pflaumii has occurred in southwestern Australia because most surveys have not targeted small, cryptic species. The population increase and spread of A. pflaumii in eastern Australia and New Zealand infer that further range expansions in southwestern Australia are likely.

This datasheet on Geophagus brasiliensis covers Identity, Overview, Distribution, Dispersal, Diagnosis, Biology & Ecology, Environmental Requirements, Impacts, Uses, Further Information.