Fish life
Key findings for freshwater ecosystem fish health from the 2026 Report Card
The basin-level grade for ecosystem fish health remains unchanged in this year’s Report Card. This reflects data collected in 2022-2023, which showed ecosystem fish health is ‘moderate’ in both the Ross and Black Basins.
​
This year, however, data has been examined at a finer, sub-basin scale (where three or more sites were sampled). At this level, ecosystem fish health varies considerably across the region.
​
In the Ross, ecosystem fish health is rated ‘poor’ in the Bohle River, and ‘good’ in both the Lower Ross River and Alligator Creek sub-basins. These results are broadly consistent with the previous monitoring period (2019-2020), indicating relatively stable ecosystem fish health.
​
In the Black Basin, a different pattern emerges. The Black River sub-basin is rated ‘very poor,’ declining from ‘poor’ in the previous monitoring period, while Crystal Creek maintains a ‘very good’ grade.
​
The most recent monitoring took place during 2025-2026, and will be included in next year’s (2027) Report Card.
The catch: fish as indicators of ecosystem health
​
Ecosystem fish health grades look at how many indigenous (native) vs non-indigenous (invasive or introduced) fish species are in a waterway, making them a useful indicator for ecosystem condition. Healthy waterways tend to support a diverse range of native species, while degraded systems are often dominated by a smaller number of non-native species.
​
The eastern rainbowfish was the most widespread native species, recorded at all 27 sampling sites. In contrast, tilapia and gambusia were the most common invasive species, recorded at 15 and 13 sites respectively.
You can think of tilapia as the “cane toad” of our waterways. They’re highly adaptable and able to spread quickly, often at the expense of native species which lose out on food and habitat. As invasive species become more dominant in our waterways, they can reduce biodiversity and disrupt the natural balance of the ecosystem.
