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Guide to New Zealand's freshwater invertebrates
Fringe gilled mayfly
Isothraulus mayfly nymphs have a flattened body form, and the double gills are extensively fringed.
Isothraulus larvae are rarely found in high abundance, but they are most common in small, slow-flowing bush covered streams in the north of the North Island.
Leptophlebiid mayflies feed by scraping diatom algae and other organic matter from stone surfaces.
The presence of Isothraulus suggests good habitat and water quality conditions, especially if other mayfly or stonefly groups are abundant. They have tolerance values of 8 (hard bottom sites) and 7.1 (soft bottom sites).