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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Dorsal view of a Amphizoa (Amphizoidae) Beetle Larva from Sears Creek in Washington
This is the first of it's family I've seen, collected from a tiny, fishless stream in the Cascades. The three species of this genus all live in the Northwest and are predators that primarily eat stonefly nymphs Merritt R.W., Cummins, K.W., and Berg, M.B. (2019).
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Posts: 2
Rob on Apr 17, 2007April 17th, 2007, 9:31 am EDT

I am new to fly fishing and I can't seem to find an answer to what line wt corresponds to what size trout.

For example, I see that 0-3 wt is for 'small' fish but how is 'small' defined? 3-4 inch or what?

Is there a table anywhere that correlates fly line wt to fish size in either fish length or fish weight?

My second question is what 'speed' of sinking line (or sinking tip) should be used when lake trolling a 'fly' for brook trout living at a depth of 12 to 15 feet?

Thanks for any help,

Taxon's profile picture
Site Editor
Plano, TX

Posts: 1311
Taxon on Apr 17, 2007April 17th, 2007, 11:15 am EDT

What I think you are really asking is what weight “rod” does one need for different sized fish, as line weight needs to correspond to the rod’s rating. In other words, if a rod is rated for 5 wt. line, that’s the weight of line you normally use on it in order for it to cast the line properly.

I would guess that a 5 weight rod is used more often than any other weight for trout fishing, and probably an 8 or 9 weight rod for salmon or steelhead fishing.

With regard to lake trolling at 12-15 feet depth, depending of the speed of troll desired, I would probably use type 3 or type 4 full sinking line.
Best regards,
Roger Rohrbeck
Troutnut's profile picture
Bellevue, WA

Posts: 2758
Troutnut on Apr 17, 2007April 17th, 2007, 11:51 am EDT
Your line weight should match your rod weight, so if you've got the rod already, you've got your answer. (Sometimes people will use a line 1 weight heavier or lighter than their rod, but you probably don't need to worry about that.)

For overall weight choice, it depends both on the fish you'll be going after and the types of flies you'll be casting. I'll give general fly size basics here, and I'll try to give fish sizes, but bear in mind that it's usually possible to land larger fish with smaller rods than what I'm suggesting. These are pretty rough guidelines and plenty of people might argue with the specifics, but they should give you the basic idea:

0-1 weight: Short casts with very tiny dry flies on very light tippets. Generally for specialists in tiny hatches like Tricos. I haven't fished with one, but should be fine for trout under 14 inches.

2-3 weight: For dry flies and very small nymphs/wets, usually used either for small stream fishing or for delicate dry-fly presentation. Should be fine for trout under 18 inches.

4-6 weight: The most common all-purpose trout rod sizes. Most people use a 5. Good for landing trout under 25 inches and casting most trout flies.

7-8 weight: Good for big streamers for trout, but more commonly used for small salmon and steelhead, or smallmouth bass.

9+ weight: For fish that could push 15+ pounds frequently or that require very large flies: king salmon, muskies, saltwater stuff.

All kinds of considerations might make you go a little heavier or lighter than this. If you're on glassy clear water with skittish fish, lighter may be better. If you're going to fight fish in strong current or have to bully them away from brush, or if you have to cast into strong wind, go a little heavier, etc.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
Posts: 2
Rob on Apr 18, 2007April 18th, 2007, 10:54 am EDT
Thanks Jason and Roger.

Perhaps you can help me with another problem...

I have 2 floating fly lines but do not know what 'weight' each one is.

Is there a way to tell?

Taxon's profile picture
Site Editor
Plano, TX

Posts: 1311
Taxon on Apr 18, 2007April 18th, 2007, 2:15 pm EDT

A fly line weight number is based on the first level 30 feet (excluding tapers). The scale is as follows:


However, as a practical matter, you could probably just take your lines into a fly shop, and get someone to give you a rough idea as to what kind and what weight they are.
Best regards,
Roger Rohrbeck

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