Beginner Guide

Fishing Freshwater Isopods – Fly Fisherman


Should you fish in a stream or river with a number of weeds, there are additionally probably freshwater isopods. These little crustaceans are constantly accessible to the trout by all seasons, they usually’re one motive why trout in tailwaters and spring creeks are sometimes so giant. (Eric Naguski picture)


This text was initially titled “Freshwater Isopods” within the Rising Tides part of the Aug-Sept 2021 subject of Fly Fisherman journal.

The modestly sized brown trout held in about 6 inches of water, positioned within the present of the eddy so it was dealing with me, although I used to be fishing upstream whereas stalking the perimeters of this central Pennsylvania limestone spring creek.

I might see the fish plainly within the brilliant solar and clear water. Fortunately I didn’t spook this one as I had the earlier fish I got here throughout. It was a sizzling midsummer day, and there have been only some leftover Trico spinners floating lifeless alongside the perimeters and eddies of the stream. My final solid had despatched the earlier fish darting for the quilt of deeper water.

I watched the fish for a couple of minutes. He wasn’t an enormous, however nonetheless a decent fish for this stream. Each minute or so, the fish moved ahead, caught its head right into a small patch of submerged aquatic vegetation, then dropped again to its unique place to feed. I instantly acknowledged that the fish was rooting round within the vegetation and knocking cress bugs, as we name them right here in Pennsylvania, free from their house within the weeds. The fish was creating its personal “hatch.” After “shaking the branches” a couple of occasions, the trout seemed down at a softball-sized rock and ate one thing from its floor.

I gently solid my evenly weighted dimension 14 cress bug sample simply upcurrent of the trout, instantly over the vegetation the trout had been rooting round in. I plainly noticed the fly drift downstream, then dangle up on the underside a couple of foot in entrance of the fish. I gently lifted the rod tip, aspiring to wiggle the hook free from the underside, and the slight motion prompted the fish to pounce. Fairly glad with the entire state of affairs, I introduced the fish at hand, and admired it momentarily earlier than it darted off into the present.

That is the trout looking that I really like, and it’s what retains me on the water within the warmth of midsummer and through the freezing snow squalls of winter. Residing and fishing in spring creek nation affords year-round alternatives.

Aquatic Crustaceans

Freshwater isopods (regionally generally known as cress bugs or sow bugs) are a number of the most essential meals sources for trout in spring creeks and tailwaters. They make up a big portion of the biomass, and can be found to the trout each minute of each hour of every single day of the yr, and the fish realize it.

Freshwater Isopods, crustaceans, sow bugs, cress bugs
Freshwater isopods—identified regionally as cress bug or sow bugs—are crustaceans that kind a big portion of the biomass in spring creeks and tailwaters throughout North America. They’re flattened and oval, and are most frequently coloured to match the stream backside. (Eric Naguski picture)

Aquatic isopods, favourite meals of trout and different freshwater gamefish, are crustaceans within the order Isopoda.  They’re associated to the terrestrial sow bugs, capsule bugs, and roly-polies you discover underneath rocks in your backyard, and look a lot the identical.

Lots of the aquatic varieties dwell in subterranean habitats (caves and comes) however there are two genera within the household Asellidae which can be of curiosity to trout anglers. These genera are Caecidotea species and Lirceus species. Each are discovered within the streams of the Jap United States, and the genus Caecidotea is extra prevalent within the West.



Morphologically, species inside the two genera are very equally formed. However typically, Caecidotea are typically barely extra slender than the extra ovoid Lirceus. Sow bugs appear to be the lesser identified of the aquatic crustaceans and don’t appear to get fairly as a lot consideration as Amphipods (scuds), however they play an essential ecosystem position in lots of spring creeks and tailwater methods throughout North America.

Sow bugs feed on decaying natural matter, most frequently plant materials, and are virtually all the time present in streams with giant quantities of aquatic vegetation. Sow bugs breed yr spherical, and the feminine carries the fertilized eggs after which holds the newly hatched younger isopods in a pouch-like construction referred to as a marsupium for 20 to 30 days. This course of known as direct improvement. As sow bugs mature they are going to have at the least 15 instars (molts), rising bigger with every molt. They grow to be adults after 5 to eight instars. The truth that sow bugs reproduce yr spherical makes them particularly essential to trout. In contrast to most mayflies, caddisflies, and stoneflies, there’s by no means a peak time or a corresponding low time when it comes to availability to trout.

The coloration of sow bugs is variable however is most frequently an olive-gray with a median dorsal “stripe” of darker pigmentation. This stripe is particularly conspicuous in Lirceus.

In some trout waters, the abundance of sow bugs is actually astounding. In a single research on the Bighorn River, Montana, researchers discovered as many as 7,213 sow bugs per sq. meter. It’s no surprise the Ray Charles Sow Bug was created there and remains to be efficient as we speak. All of the weedy Western tailwaters have cress bugs, as do Western spring creeks just like the Paradise Valley spring creeks in Montana, and California spring creeks like Hat Creek, Sizzling Creek, the McCloud River, and the Fall River.

Only a few of the trout waters right here in Pennsylvania with good sow bug populations embody all of the limestone spring creeks of Cumberland Valley (Letort, Huge Spring, Yellow Breeches, and others), Spring Creek in Centre County, and Spruce Creek in Huntingdon County.

They’re additionally within the spring creeks of the Shenandoah Valley in Virginia (Mossy Creek and Beaver Creek), within the West Department of the Delaware River, and in most of the TVA tailwaters within the South together with the South Holston, the Watauga, and the Toccoa rivers. This record will not be inclusive, as cress bugs are extremely widespread, essential meals sources for trout in virtually all weedy environments.

Flies and Methods

Sow bugs are dorso-ventrally flattened and both formed like a soccer (ovoid) or not fairly as large and formed extra like a Popsicle stick, rounded on the ends. The form of sow bugs dictates the design of the flies.

Cumberland Valley legend Ed Shenk was the primary fly fisher to put in writing about imitating freshwater isopods in his article  “The Cress Bug” within the January 1972 subject of Fly Fisherman. Many of the subsequent sow bug patterns developed in North America have Shenk’s Cress Bug DNA in them. Three extra fashionable patterns well-liked on the spring creeks of the East are Jake Villwock’s SYE Sow Bug (Easy But Efficient), and beadhead Jiggy SYE. One other efficient sample is my very own HG (Sizzling Glue) Cress Bug. I’m assured you should utilize any one among these three patterns and achieve success imitating sow bugs wherever.

Freshwater Isopods, crustaceans, sow bugs, cress bugs
Shenk’s Cress Bug, first described within the January 1972 subject of Fly Fisherman, is the grandfather of most cress bug imitations tied as we speak, and it nonetheless catches fish. (Eric Naguski picture)

There are lots of different nice sow bug patterns on the market—George Daniel’s Joe’s Fur Cress Bug is one other that involves thoughts. Ask any skilled spring creek angler, and they’ll both have their very own sample, or inform you which preexisting patterns is their favourite.

Your fly shade ought to be within the olive-gray vary. Get to know the sow bugs in your native waters to customise the colours of your patterns to match what’s widespread. If you’re touring to fish, and suppose you might run into some sow bugs, name an area store. They’ll positively level you in the fitting path. However as a common rule, I prefer to have a couple of patterns in olive, olive-gray, olive-tan, and some which can be primarily grey with a light-weight quantity of olive and tan. Some of the essential traits is the darkish dorsal median stripe that’s normally a darker olive-brown. Sizes vary from #10 to #18, however typically #14 and #16 are the perfect sizes to begin with.

An essential consideration for a great sow bug sample is the load. Even when it appears to be like actual to you, a sample that’s too closely weighted won’t tumble alongside the underside like the true sow bug. I’ve spent in all probability approach an excessive amount of time simply watching what occurs to sow bugs when one thing causes them to lose their grip, and they’re picked up by the present. They tumble by the water column, slowly sinking to the underside. Sow bugs which can be strolling throughout the stream backside and caught by the present simply flip time and again like a rolling automotive till they will regain a maintain on the underside or some underwater vegetation or a rock.

You need sufficient weight in your fly to get it close to the underside, however not a lot weight that it doesn’t transfer naturally. Should you want additional weight, add split-shot.

I like to recommend fishing sow bugs with 4X to 6X fluorocarbon tippet. Most of our limestone streams are exceptionally clear, and the much less the trout see of your tippet the higher.

It’s also possible to fish sow bugs as a part of a dry/dropper rig—there isn’t any denying that is an efficient technique to fish this fly. The dry-fly alternative ought to be dictated by the point of yr. Within the winter, a dimension 14 black stonefly sample is an efficient alternative. Within the spring, caddisflies grow to be extra related. As you progress into summer time, a beetle, hopper, or cricket makes extra sense.

Sow bugs can be fished as you’ll another nymph, underneath an indicator or as a part of a tight-line nymphing rig. That is particularly efficient when circumstances forestall you from sight fishing the fly to a selected fish. A drop-shot rig positions the heavy split-shot on the backside of the rig, with the fly on a dropper above it to permit enough motion of the sow bug sample through the presentation. An alternative choice for a tight-line rig is to make use of a closely weighted backside fly to get the sow bug into the right place within the water column. Both rig can be used with an indicator.

Sight Fishing

Should you actually wish to up your recreation, attempt sight fishing a single sow bug to a selected fish—it’s a rewarding and completely visible expertise that paints eternal recollections in your thoughts. Nobody forgets the second when a wild fish feels the sting of the hook and goes berserk within the confines of a small spring creek, and a quiet pastoral setting instantly turns into a venue for mayhem.

Freshwater Isopods, crustaceans, sow bugs, cress bugs
Sight fishing to a feeding trout with a single sow bug is a rewarding and completely visible freshwater looking expertise. If you wish to add an indicator, use a sparse yarn-type indicator so it lands softly with out the “plop” which will spook fish feeding in shallow water. Even with an indicator, attempt to watch the fish, not the indicator, as trout typically take the fly with out transferring the indicator. (Eric Naguski picture)

A very good sow bug sample could make these sorts of recollections occur. You’ll be able to sight-fish a single sow bug sample with no dry or indicator. A tender indicator reminiscent of a Dorsey indicator or New Zealand Strike Indicator is rather more efficient in these conditions as a result of they land softly. The very last thing you wish to do is plop an enormous foam or plastic indicator on high of a pressured wild fish.

If you’re sight fishing with a dry/dropper or indicator rig, just be sure you watch the fish, not the indicator or dry. The indicator is there primarily to offer you an thought of the place your sow bug is. You need to be watching the fly, or at the least the fish you’re after.

I typically go with out the indicator and use a single sow bug with a small split-shot about 6 inches above the fly. This system will not be for everybody, and infrequently a dry/dropper or indicator rig makes issues barely easier. None of that is straightforward fishing, however I choose the stealth of casting to single trout utilizing only a single sow bug and a small split-shot. It’s about as technical as you may get, however the payoff when you’re profitable is superb.

I can’t inform you what number of occasions I’ve watched a fish eat a sow bug with out transferring the indicator. On a day with good lighting, you’ll be able to have a transparent view of the fish’s response to your fly, and when all of it comes collectively and you may feed your sow bug to a giant wild trout, the expertise is like no different.

When you’ll be able to find a feeding fish, you will discover essentially the most success by presenting your providing fly first. By this I imply that the fly ought to attain the fish first, earlier than another portion of your line, chief, or tippet. One of the best ways to do that is with a downstream presentation. However to be in place to current the fly on this method, you’ll have to be upstream of the fish. This places you within the precarious place of probably spooking the trout.

Freshwater Isopods, crustaceans, sow bugs, cress bugs, rainbow trout
When all of it comes collectively and you may feed your sow bug to a giant wild trout, the expertise is like no different. (Photograph courtesy Eric Naguski)

I like to recommend maintaining your profile as little as attainable, and making the solid from the aspect and from a distance that retains you out of the fish’s line of sight. Place the fly a distance above the fish that permits the fly enough time to sink to the underside. You need the fly to be tumbling alongside the underside naturally, simply because it comes into the trout’s feeding lane.

Measure the space to the fish with one or two false casts, add a pair ft to that distance, and on the supply, cease the rod abruptly through the ahead stroke, so the fly lands above the fish with just a little slack within the chief. It will assist keep away from drag throughout your presentation.

Should you can’t get into place to current the fly downstream to the fish, and you could strategy from downstream, you’ll must make additional effort to ensure you don’t line the fish along with your solid. Angle the solid upstream, inserting the fly and chief far sufficient upstream of the fish to permit time in your fly to sink.

Should you can’t get into place to make an angled upstream solid, and you could solid from instantly downstream, use a curve solid to put the fly instantly above the fish and the remainder of your chief and fly line off to the aspect of the fish, lowering the probabilities of spooking your goal.

Even from downstream, keep low whenever you strategy the trout, and make as few false casts as attainable. The sight-fishing recreation may be actually addictive. When you meet with just a little success, you might simply hold coming again for extra. And since sow bugs are sometimes present in trout streams which can be fishable year-round with comparatively constant circumstances it doesn’t matter what the time of yr, you’ll have loads of alternatives to attempt to feed your finest sow bug imitation to what might be the trout of a lifetime.

Fly Recipes

Freshwater Isopods, crustaceans, sow bugs, cress bugs, fly recipes, fly tying, fly fishing
(Eric Naguski picture)

Jiggy SYE (left)
(Jake Villwock)
HOOK: #12-18 Tiemco 450BL.
BEAD: 2.8 mm slotted tungsten bead, mottled brown.
THREAD: Grey 8/0 UNI-Thread.
WEIGHT: 0.025″ lead wire.
DUBBING: Sow bug Sow-Scud Dubbing.
DORSAL LINE: Loon UV Circulation.

HG CRESS BUG (center)
(Eric Naguski)
HOOK: #12-18 Tiemco 230BL.
THREAD: Brown Veevus 12/0.
WEIGHT: 0.015″ lead wire.
DORSAL STRIPE: Darkish brown Wee Wool.
BODY: Wapsi Smokey Olive Sow Scud Dubbing.
SHELL: Sizzling glue trimmed to form.

SYE Sow Bug (proper)
(Jake Villwock )
HOOK: #12-18 Tiemco 230BL.
THREAD: Brown Veevus 12/0.
WEIGHT: 0.015″ lead wire.
DORSAL STRIPE: Darkish brown Wee Wool.
BODY: Wapsi Smokey Olive Sow Scud Dubbing.
SHELL: Sizzling glue trimmed to form.

Freshwater Isopods, crustaceans, sow bugs, cress bugs, book, Eric Naguski

Eric A. Naguski has a Bachelor of Science in Biology from Millersville College, with a give attention to aquatic entomology and ecology. He’s the creator of Favourite Flies for Pennsylvania: 50 Important Patterns from Native Specialists (Stackpole Books, 2021). He’s a information and proprietor of Riseforms Fly Fishing in Boiling Springs, Pennsylvania and serves on the boards of Cumberland Valley Trout Limitless and the Pennsylvania Fly Fishing Museum Affiliation.



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