Introduction

Fish are the most diverse of the vertebrate groups, having about 30,000 species worldwide, with Australia having approximately 3,600 fish species (mostly marine).

Australia has relatively small freshwater fish fauna (~200 species), not surprising really when you consider we live on the driest inhabited continent.

Species diversity in freshwater fishes declines with increasing distance from the sea (as species with marine life stages progressively drop out of the fish community) and increasing altitude (as the range of habitats becomes more restricted).

The upper Murrumbidgee catchment has ~16 fish species (Table 1) with x native and y alien species recorded.

There are six fish species listed as threatened under National, State or Territory legislation and three of these occur mainly in upland streams of the Canberra region:

• Macquarie Perch
• Trout cod
• Two-spined blackfish

The other threatened ‘fish’, (Murray Cod, Silver Perch and Murray River Crayfish) occur in more lowland locations such as Murrumbidgee River.