Salty Goldfish? Goldfish can use wetlands as ‘bridges’ to invade new rivers

The Goldfish (Carassius auratus) is arguably the most popular and well known ornamental fish species and this popularity has been responsible for feral populations of Goldfish being recorded from almost every Australian state and indeed throughout much of the world. While generally regarded as a freshwater fish, a preliminary study of the fish faunas of the Vasse-Wonnerup by the authors recorded Goldfish in the system during a time when the estuary was salty (~17 ppt, i.e. half full strength seawater). A population of Goldfish has been known to occur in the Vasse River since the early 1990s, however, it was incorrectly thought that the Goldfish could not penetrate into the Ramsar listed Vasse-Wonnerup wetland, as, at certain parts of the year, the system became salty. Worringly, in Europe, research has shown that several introduced freshwater fish (e.g. the Zander; Stizostedion lucioperca) have been able to survive in estuarine waters for long enough to use these systems as a ‘salt bridge’ to invade other, previously uncolonised, freshwater environments. As Goldfish are known to resuspend nutrients and increase turbidity during their foraging, exacerbate algal blooms, decrease aquatic vegetation and predate on and compete with native species, they could pose a major threat to health of the Vasse-Wonnerup wetland and its other tributaries. This poster and presentation document (i) the abundance of goldfish in seven regions of the Vasse-Wonnerup wetland and in each of its four tributary rivers, including the Vasse River, which has an abundant Goldfish population, seasonally over 18 months; (ii) the results of a set of laboratory experiments to test the acute and gradual salinity tolerances of Goldfish from the Vasse River and (iii) a comparison of these tolerances with those obtained from Goldfish bought from a pet store. The management implications of these findings are then discussed.