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).
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.
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