INTRODUCTION
Invasive species, including fishes, are now recognised as a major threat to global
biodiversity (Witte et al. 1992; Cambray 2003; Njiru et al. 2005; Dudgeon et al. 2005)
and can cause significant economic damage (Perrings et al. 2000; Pimental 2002; Cox &
Kitchell 2004). Webb (2003, 2008) documented the history of introductions of non-native
species into Australian waters and especially into tropical northern Queensland. Of
concern was that in recent decades the rate of introductions appears to be accelerating.
Historically, many introductions of non-native fish species, for example, for developing
commercial fisheries and for the aquarium trade have occurred with little or no rigorous
assessment of the risk these species may have posed to native aquatic communities if they
entered open waterways and established feral populations. The increasing recognition of
such threats resulted in the development of risk assessment protocols in several countries
including Australia to regulate the import and release of non-native fishes, although such
protocols were largely qualitative and limited due to lack of ecological information on
target species. Kolar and Lodge (2004) noted that the screening method most often used
for aquatic species involved deductive risk assessment, where inferences about a risk are
based on what is known or has already occurred. This method is based on identification
of species with a history of invasion and use of selection criteria to identify those with a
higher potential of becoming invasive at a given location. They argued that this method is
not based strictly on species characteristics, although attributes may be included in the
selection criteria, usually in the form of subjectively ranked scores to determine category
membership.