Exotic Aquatic Organisms - International Development Research ...

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Arthington 1988; Lloyd 1987); G. affinis attacks and eats fish fry in aquaria (JoFnson 1976;
Meffe 1985; Lloyd 1987). It is noteworthy that several small-bodied native fishe; seemingly
affected by the mosquitofish in Australia have low fecundity (Milton and Arthington 1983b,
1984, 1985) but others do not.
Brown trout, S. trutta, Chinook salmon, Onchorynchus tshawytscha and redfin Perca
fluviatilis, feed selectively on small endemic fishes and fish fry and may have affected the
numbers of galaxiids, pigmy perch, N. australis, and golden perch, Mac quara ambigua
Richardson, in southern rivers (Fletcher 1986).
Impacts of Predation in Invertebrates
G. affinis has had destructive effects on invertebrate populations in field situations
(Stephanides 1964; Legner and Medved 1974) and in controlled experiments. Taxa such as
beetles (Walters and Legner 1980), back swimmers (Huribert and Mulla 1981), rotifers,
Crustacea (Huribert et al. 1972) and molluscs (Rees 1979) have been affected.
In Brisbane streams, G. affinis feeds on small terrestrial insects and immatu:e stages of
aquatic insects in the drift and amongst aquatic plants, actively selecting very small prey
(Arthington 1988). Such size selective feeding might affect the structure of invertebrate
communities by altering recruitment of various taxa. However, the impacts of G. affinis and
other invertebrate-feeding fishes on assemblages of invertebrates have not beer. studied in
Australia and require attention.
Brown trout feeding may have caused the decline of the Tasmanian mouni am shrimp,
Anaspides tasmaniae, and has eliminated or reduced several Plecoptera and Trichoptera in
Victorian streams (Fletcher 1979). In experimental ponds, carp have caused the decline of a
species of Daphnia (Fletcher 1986).
Introduction of Parasites and Diseases
Many biologists have opposed the traffic of introduced aquarium species into Australia due
to concern that diseases and parasites may also be introduced (Hoffman 1970; Me Kay 1984).
There is already evidence that disease organisms have entered Australia via the aqu irium trade.
Goldfish ulcer disease entered Australia this way (Trust et al. 1980) and has reccntly spread
rapidly to wild stocks (Whittington et al., in press). Langdon (1986) and Langdon and Humphrey
(1987) described a new viral disease of redfin, P. fluvitailis. Concern over imported lish diseases
has led to the establishment of quarantine facilities at major ports handling aquarium stocks
(McKay 1984).
Fish introductions were responsible for importing fish parasites such as fish louse, Argulus
(Williams 1980) and anchorworm, Lernaea cyprinacea (Roberts 1978; Hoffman a:id Schubert
1984). However, although G. affinis is host to 22 species of parasites in North America, there is
only one Australian record of parasitism, a species of Lernaea found on mosquitofish from the
River Murray (Lloyd 1984, 1987). The incidence of imported parasites in Australian endemic
fishes is unknown. Moyle (1985) noted that endemic Californian fishes seem at time; to be more
heavily parasitized by exotic parasites such as L. cyprinacea than do introduced fishes.