Why can introduced trout affect galaxiid and retropinnid fishes in Australia and New Zealand?

Introduced trout, such as the rainbow trout and brown trout, significantly impact native galaxiid and retropinnid fishes in Australia and New Zealand because they act as large, aggressive predators in environments that previously lacked such species.1

When these salmonids are introduced into lakes containing abundant food sources but no native large predator fish, they flourish and grow rapidly to trophy sizes. In these ecosystems, the introduced trout feed avidly on their distant relatives—the smaller, native galaxioid fishes—often leading to a decline in the native populations.1