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Latest research into the ecological impact of the invasive aquatic pest rocksnot shows its effect on insects and crustaceans in the water - crucial foods for trout and other fish - may be less severe than first thought.
"The studies have found increased numbers of bottom-dwelling invertebrates living in association with didymo algal mats," Biosecurity New Zealand scientist Dr Christina Vieglais said.
"This is meaningful for our native fish, most of which feed on these types of invertebrates".
Research had also shown that the highest densities and biomass of "drift invertebrates" were near the river sites with medium to high growths of the pest, didymosphenia geminata.
The main sources of food for trout are invertebrates which emerge from the river bottom and drift downstream.
So far, the pest has spread to 52 rivers and five lakes in the South Island, covering nine catchments.
Dr Vieglais told a seminar held in Wellington on Tuesday that "the best way to control the spread of didymo is for all freshwater users to check, clean and dry their equipment between waterways".
- NZPA
