Iso nymphs

Aaron, tell us about Isonychia nymphs, they are often a productive fly this time of year in many streams in the Northeast.

Hey buddy...

You could write a book about this single topic.

Isonychia nymphs are readily available to trout from late May through Mid October on most of our trout streams in the Northeast.
These nymphs are very fast and erratic swimmers. They are also larger than most mayflies with the exception of the larger and more notable Green and Brown Drakes. These flies used to have several sub-species now they are all classified as Isonychia Bi-color. The nymphs are charachterized by their three short stubby but prominent tails. They also have very easily recognizable gills along their sides and are a charcoal/olive color. They look like very sleek swimming machines, which, in reality is what they are.

Since this hatch is so long in duration trout get great opportunity to get used to feeding on these insects. You would not call this a "super" hatch because the hatch intensity on most streams in the region is not high. However, the nymph density is very high. These nymphs inhabit faster boulder strewn water which is found on streams such as, the Housatonic, Beaverkill and the Lower West Branch of the Delaware as well as the Lehigh River in Pennsylvania. These are four streams that in my opinion have some of the best Iso hatches in the region.

I have been told byh my friend Tony that he sees tons of immature Isonychia nymphs in the months of February and March when he is sampling for insects. However,, at this time of the year I find stoneflies, scuds, small caddis larvae and aquatic worms to be more effective for catching trout during the late winter. This would indicate that even though behavioral drift is occurring with these flies they are not of importance as far as trout food is concerned at this time of year.

I start to use Iso nymphs when I go to the river and see their nymphal shucks on the rocks. This is a mayfly that migrates to the side of the stream to hatch. You need not even see the adults to know that they are hatching. All you need to do is check out the rocks prior to wetting a line and look for the shucks. This a time of the year when I get really excited. I know that I am in the game on any stream that I choose to fish as long as I have something that represents an Isonychia tied to the end of my tippet.

There are many different immitations that you can use to catch trout sub-surface during this hatch. My favorite is to use a nymph that closely immitates the naturals. The nymphs that I use can range from a Prince nymph which would be considered impressionistic to a very realistic immitation such as a Rob's Realistic Iso nymph. When fishing on heavily pressured streams like the Delaware, I like to use nymphs that very closely "match the hatch". On rivers like the Housatonic, where the trout are more opportunistic, I find that a simple prince nymph or a zug bug works wonders on the trout. Don't get me wrong there are times when you need to use a more relistic nymph when fishing on less pressured water.

I have also found that fishing wet flies during this hatch can be quire effective as well. Since the nymphs are fast swimmers swinging three wet flies through the riffles can yield fish that would not touch even the best iso nymph imitations. I found swinging wet flies to be ultra-productive on the South Branch of the Raritan. The wet flies that worked the best were the Picket Pin and the Leadwing coachman. When the trout would slash at the surface for the emerging adults I would swing the flies over the trout and and more often than not this would draw some viscious strikes.

When I rig my line for this hatch I use my standard nymph rig. I tie on my larger Isonychia nymph and trail it with something smaller like a rs2 or a wd40. Usually when the Isonychia are hatching you can be very sure that there are BWOs hatching at the same time as well.
I use a fair amount of weight so that I am right on the bottom because these nymphs inhabit such fast water and I think the trout really key on the nymphs that just come off the bottom to hatch or get washed off the rocks in the swift current.

When I fish wet flies during this hatch I use the Joe Humphries wet fly leader. I tie the first two wet flies on 3X droppers. I feel that the size of the tippet has little effect on whether or not the trout are going to take your offering. Most of the time I do not use weight when I am fishing with wet flies. However, there are times when I do feel the need to use weight, especially in the deeper and faster runs.

I hope that these tips/suggestions might shed some light on how and why to fish Isonychia nymphs.

The Iso hatch on the Esopus was in full swing last week. The fish were going bonkers over them. Unfortunately most of the fish are too small to be able to take an iso nymph imitation. I suppose the naturals they can just fold in two. Giant golden stones were present too.

Aaron, what's the proper dubbing color on an Iso nymph? I've heard a blend of black with brown (rusty-ish, red)? What an enlightening post, thanks.

Aaron- I've found when swinging wet flies that sometimes its very productive to use a nymph(s) in my brace, especially as the tailing fly? I thank Mr. Dave Hughes and his wonderful book on wetflies for that idea. Do you ever use iso nymphs on your wet fly brace? I haven't tried this, but I know in the gorge I tend to get my most takes on large olive and black hare's ears as the tailing fly with traditional winged and soft hackles as my dropper flies. (Maybe this is now entering the realm of a wet fly discussion and should be moved over there). Thanks for your input! BTW, I'll send you some of my isos and some of those emu nymphs on saturday.

[quote author=DAVEtheRAVE link=topic=885.msg5157#msg5157 date=1190175414]
Aaron, what's the proper dubbing color on an Iso nymph? I've heard a blend of black with brown (rusty-ish, red)? What an enlightening post, thanks.
[/quote]

I use a blend of rabbit in the following colors:

Maroon (Dark rust), Dark Olive, Purple, Black - roughly 50/30/10/10 - when I'm not using a Prince nymph ;)

February and March, I have found a lot of Amaletus (I think, it's been a while since I've ID'd insects) nymphs, which look similar to Isos, but a little smaller

Thanks Slo, very helpful. I'll start tying these up now. What is the most effective way to "blend" dubbing? It is enough to mix them between your fingers while applying them to the thread (which most often gives strands of different colorings, not really a true "blend"), or is it best to cut the dubbing into smaller fibers/pieces and mix?


Btw, I finally got the double edged blades at CVS, thanks.

Best way to blend dubbing, so I'm told, is in a coffee grinder. Your can get one of the standard braun ones for like 16 bucks.

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So Aaron, what is your current favorite & most effective Iso Nymph dressing? Care to give it up to the TPO faithful?

[quote author=DAVEtheRAVE link=topic=885.msg5167#msg5167 date=1190261506]
Thanks Slo, very helpful. I'll start tying these up now. What is the most effective way to "blend" dubbing? It is enough to mix them between your fingers while applying them to the thread (which most often gives strands of different colorings, not really a true "blend"), or is it best to cut the dubbing into smaller fibers/pieces and mix?[/quote]

Sorry about the delayed response.

I usually blend them by hand. I dont just mix them a little while putting them on the thread, as you stated this just results in clumps of different colors. That said, you can do an effective job by hand.

I usually take a few small clumps of the dubbings I am mixing (no need to cut unless the pattern calls for it) and pinch them between my thumb and finger, then with the other hand pinch the clumps and pull them away from the other hand (retaining a grip on the clump). I repeat this a bunch of times til the clumps are well mixed, usually about two minutes or less. You can easily do this with the coffee grinder but if you have added synthetics, they get chopped rather than blended, so you can often only use one quick burst, then if you need to adjust the blend, you must do it by hand or risk chopping the synthetic material too much.