When does the Isonychia japonica hatch?

May–October, typically 14:00–20:00. It starts from about 11°C, peaks around 16°C and tails off by 23°C.

What flies imitate the Isonychia japonica?

Sakasa Kebari, CDC Olive Emerger, typically on a #14–12 hook.

How big is the Isonychia japonica?

Spinner stage: 10–13mm. That matches a #14–12 hook.

Mayfly · Aquatic insect

Isonychia japonica

Size

10–13mm

Hook size

#14–12

Hatch window

Season May–OctoberPeak time 14:00–20:00

Water temperature

16° peak

11°23°

How fish feed on it

By the time the spinners are down the fly has finished its job and is simply lying there, spent, wings flat in the film, going nowhere. Trout know the difference between something alive and something that's stopped trying, and they take spinners with a quiet, unbothered sip that's easy to miss if you're still watching for something splashier. Look for them on the glides and in the slack water, wherever the current gathers what's left.

Flies that imitate this

Sakasa Kebari

CDC Olive Emerger

Ecology

Rivers onlyFreestone rivers

Where you'll find this

East AsiaPresent

Present throughout

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