I’m often asked what fly rod size (or line weight) is needed for a particular kind of fish. As usual with most fishing questions, the answer is: That depends….

A 9-foot, 5-weight model is often cited as a good “all around” trout rod, but that’s only true as long as one plans to fish ordinary, trout- size flies. If you’re planning on throwing big heavily weighted streamer flies with the same rod, you’d be better off with a 6- weight, for example. In that case, the heavier line has enough mass to carry larger flies in the air.

The other day someone asked if an 8-weight is good for pike. The answer again is yes, but it depends a little on what flies you’re planning on casting. Big pike-style streamers made of feathers or synthetic hair don’t absorb lots of water so they don’t become too heavy in casting with an 8-weight. A big, black rabbit-fur leech, on the other hand, is an excellent pike fly but absorbs lots of water, becoming very heavy and awkward on the end of an 8-weight line. In that case, you might be better of with a 9-weight.

In both examples, it’s not a matter of how hard you can pull with the rod once a fish is hooked. Fly size and weight, along with conditions such as windy or calm, will most importantly dictate rod choice. Big fly, big rod. Little fly, light rod. Windy day, heavier rod. Calm day, lighter rod.

Once those equations are satisfied, your choice of a rod will be both easier and more fun to cast. And it will almost always be sufficient for whatever battles you might encounter with a fish.