Journal of the Royal Society of Western Australia, 90; 151-156, 2007 
Feral Goldfish {Carassius auratus) in Western Australia: 
a case study from the Vasse River 
D L Morgan' & S J Beatty- 
' Centre for Fish & Fisheries Research, Murdoch University, South St Murdoch, WA 6150. 
’ Kl D.Morgan@murdoch.edu.au 
S.Beatty@murdoch.edu.au 
Manuscript received March 2007; accepted July 2007 
Abstract 
Minimal information is available with regard to impacts of wild populations of Goldfish; despite 
being one of the most widely introduced freshwater fishes of the world, and arguably the most 
popular ornamental fish species. During a control programme for a population of feral Goldfish in 
the Vasse River, Western Australia, aspects of population demographics and diet were examined. 
A relatively high growth rate was found with fish, on average, attaining -180 mm TL at the end of 
their first year of life, a period that coincided with first maturity. Goldfish were relatively long- 
lived with the oldest fish recorded being in its 11'*’ year of life. The diet was dominated by detritus 
that was largely comprised of blue-green algae. The potential of this species to exacerbate algal 
blooms within nutrient enriched environments is discussed. 
Keywords: feral goldfish, Carassius auratus, Vasse River, Western Australia, 
Introduction 
Tire establishment of introduced fishes outside their 
natural range is often facilitated by a wide tolerance to 
environmental regimes, maximisation of reproductive 
potential, high genetic diversity and tendency for good 
dispersal mechanisms (r-strategists) (Stauffer 1984). An 
expression of a broad diet {e.g. omnivory) and the ability 
to tolerate degraded habitats also enables exotic species 
to exist and thrive in foreign environments. Within 
Australia, examples of omnivorous fish species that are 
highly adaptable to a wide range of environmental 
conditions include some of the poeciliids, cichlids and 
cyprinids; groups that are all traditional aquarium 
species but are naturally absent from the country (see 
Morgan ct al. 2004). While the ecological impacts of some 
members of these groups are well understood, there is 
little information with regard to one of the most widely 
introduced freshwater fishes of the world, i.e. Goldfish 
(Carassius auratus). As arguably the most popular and 
well known ornamental fish species, it is not surprising 
that feral populations of Goldfish have been reported 
from almost every state of Australia (McKay 1984, Kochn 
& MacKenzie 2004) and indeed are now found 
throughout much of the world (e.g. Fuller et al. 1999, 
Gido & Brown 1999, Skelton 2001). It is also established 
in almost every state of the United States and is thought 
to be the first foreign fish species introduced into that 
country (e.g. Fuller et al. 1999). Goldfish have been 
implicated with the introductions of parasites to South 
Africa and Australia (Fletcher & Whittington 1998, 
Mouton et al. 2001, Hassan, Morgan, Beatty & Lymbery 
unpublished data) and with the decline of a number of 
native fishes in the U.S. (Deacon et al. 1964, Moyle 1976). 
© Royal Society of Western Australia 2007 
Within Western Australia, Goldfish are generally 
restricted to the south-western corner of the state in the 
vicinity of major population centres where they appear 
to be most successful in modified or degraded waters 
(Morgan et al. 2004). Tlie only previous biological study 
(growth and feeding) of wild Goldfish populations in 
Australia was conducted by Mitchell (1979) who used 
scales to age fish from South Australia, while Izci (2001) 
determined growth rates and age and sex compositions 
for a wild population of Goldfish in Lake Egirdir, Turkey. 
The main aim of this study was to implement an ongoing 
control programme for Goldfish in the highly nutrient 
enriched Vasse River and thereby reduce the biomass of 
the species. Secondary aims were to examine the 
distributions, habitat associations, age compositions and 
growth and diet of Goldfish and to develop an 
understanding of factors contributing to its success in this 
and other nutrient enriched waterbodies. 
Methods 
Study site 
The Vasse River, in south-western Australia, is - 45 
km long with a catchment of approximately 270 km^. 
About 60% of the catchment is cleared and heavily 
modified, with much of the natural flows diverted to 
drainage canals for flood mitigation (Pen 1997). Much of 
the Vasse-Wonnerup estuarine lagoon, which is roughly 
1.5 km wide and 25 km long, stretches behind narrow 
coastal dunes covering an area of 1000 ha, is cleared with 
the hydrology having been largely modified by drainage 
and tidal barriers and is threatened by eutrophication 
with the system no longer functioning as an estuary 
(Jaensch & Lane 1993, Pen 1997). Regardless, the system 
still provides important habitat for waterbirds and is 
151 
