Iso's are probably the mayfly I know the least about and have only fished a hatch maybe 3 or 4 times. The only place I've fished them was the BK. I've never seen them in NJ though they may be here, I don't know.
DC, can you elaborate on them?
Cdog
Not sure what you want to know but I'll elaborate about nothing specific.
Typically, as nymphs, they can be found around underwater plants and rocks. They are avid swimmers so bouncing from rock to plants isn't uncommon. I watched them for quite some time and they definitely don't stay in one place for any long period of time. ISO nymphs work great because of this reason... From what I've witnessed, they can't out-swim a trout whereas a nymph emerging such as a
March Brown, is a bit harder for the trout. The March Browns shed their nymphal skin underwater then swim to the surface to spread their wings. I suppose technically, they hatch underwater whereas the ISO nymph crawls out from the water and onto land. I have a video of this somewhere.
Al Caucci's Hatches II as well as the Pocket Guide, mentions that in places like the Delaware River where the streams are large with nothing to crawl out to, they will in fact hatch in the water film. This is where the ISO Emerger kicks ass!
The image of the ugly purple fly was picked up in Montana about 5 years ago. I laughed at it until I started catching fish. I figured I'd pick a few up and try them around here for the ISO's. These things kick some ass on the Delaware river. Try them out.
The Parachute ISO is pretty standard issue... Nothing special, floats like a cork for about 6 seconds then sinks like a brick.
Just kidding.
Then the CDC Emerger. On the Delaware, this is probably the most effective ISO pattern for me. (notice the "for me"). I'm not sure what others are catching them on but I manage to do pretty good with this pattern.
Of course, if none of these work for you, try on a nice big ADAMS. You can't go wrong with this fly!
There is also the Weamer Truform version, but I haven't tried this one yet. I have a few of these that I purchased a few weeks ago. I'm sure they are ISO's just slapped into the Hendrickson barrel (probably ran out of Hendricksons!)
The ISO's are larger than the Hendricksons, so it was pretty easy to spot this. Anyone not knowing the difference, most likely picked them up and figured, "it's Hendrickson season, it's marked as a Hendrickson, must be a Hendrickson"... these are the guys who of course don't know their asses from their elbows.
Here's a little description I wrote a while back:
'Gray Drake' - North Eastern Fly Fishing's Online Photo Gallery
and of course, more photo's of ISO's.
Isonychia - North Eastern Fly Fishing's Online Photo Gallery
I guess that's about it for now... Anything else?
***CLICK PHOTO'S TO ENLARGE***