The Main line is the fishing line that is spooled on a fishing reel. This line is usually changed once per year, or more, depending on how often the reel is being used.
For trout and similar small fish, 4 or 6lb test main line is usually used. For small salmon such as pink and coho salmon, 8 to 12lb test main lines are usually used. For larger salmon such as chinook salmon, and steelhead, 12 to 20lb test main lines are usually used. For sturgeon and halibut, the main line used can be up to 80lb test.
When choosing the main line, one should consider what reel is being used. The reel usually indicates what strengths of the main line are acceptable. Lines that are heavier than the acceptable strengths can damage the reel when used.