A fishing line is a flexible, high-tensile cord used in angling to tether and pull in fish, in conjunction with at least one hook. Fishing lines are usually pulled by and stored in a reel, but can also be retrieved by hand, with a fixed attachment to the end of a rod, or via a motor.
Fishing lines generally resemble a long, ultra-thin rope, with important attributes including length, material, weight and thickness. Other factors relevant to certain fishing environments include breaking strength, knot strength, UV resistance, castability, limpness, stretch, abrasion resistance, and visibility. Traditional fishing lines are made of silk, while most modern lines are made from synthetic polymers such as nylon, polyethylene or polyvinylidene fluoride ("fluorocarbon") and may come in monofilament or braided (multifilament) forms.
Fishing with a hook-and-line setup is called angling. Fish are caught when one are drawn by the bait/lure dressed on the hook into swallowing it in whole, causing in the hook (usually barbed) piercing and anchoring into the mouthparts, gullet or gill, resulting in the fish becoming firmly tethered to the line. Another method is to use a straight gorge, which is buried in the bait such that it would be swallowed end first, and the tension along the line would fix it cross-wise in the quarry's stomach or gullet and so the capture would be assured. Once the fish is hooked, the line can then pull it towards the angler and eventually fetch it out of the water (known as "landing" the fish). Heavier fish can also be landed with a landing net or a hooked pole called a gaff.
Trolling is a technique where one or more lines, each with a fishing lure at the end, is dragged through the water. Trolling from a moving boat is used in big-game and commercial fishing as a method of catching large open-water species such as tuna and marlin. Trolling can also be used when angling in freshwater as a way to catch salmon, northern pike, muskellunge and walleye. The technique allows anglers to cover a large body of water in a short time.
Longline fishing, also known as a trot line is a commercial fishing technique that uses many baited hooks hanging perpendicularly from a single line.
Snagging is a fishing technique where a large sized hook is used to pierce the fish externally in the body (like a gaff) instead of inside the mouth, and is therefore not the same as angling. Generally, a large treble hook with a heavy sinker is cast into a river containing a large amount of fish (such as salmon) and is quickly jerked and reeled in. Due to the often illegal nature of this method some practitioners have added methods to disguise the practice, such as adding bait or piercing the jerking motion.
Traditionally, only a single thread of line is used to connect the hook with the rod and reel. However, most modern angling setups use at least two sections of line joined with a bend knot (such as the famously named fisherman's knot). Occasionally a swivel might be used to join the lines and reduce the bait/lure spinning due to the inherent line twisting from a fixed-spool reel.
Leonard Mascall, in his book from 1596 titled “A Booke of fishing with Hooke and Line, and of all other instruments thereunto belonging.” followed in many ways after Dame Juliana Berners, has an excerpt establishing silk worms in the area of England at that time:
..."In May, take the stone flye or Caddis worme, and the bobbe worme vnder the Cowtorde: also ye may take the silke worme, and the baite that breedeth on a Fearne leafe." ...
And another excerpt explaining compiling a silk leader-line for a catgut fly-line.
"...whippe it so faire as yee shall see good, then next your hooke at the bought put throw your silke or haire in going round about the hooke three times, then plucke first your silke or haire..."
So back then there was silk and horse hair used for angling.
As written in 1667 by Samuel Pepys, the fishing lines in his time were made from catgut. Later, silk fishing lines were used around 1724.
Modern fishing lines intended for spinning, spin cast, or bait casting reels are almost entirely made from artificial substances, including nylon, polyvinylidene fluoride (PVDF, also called fluorocarbon), polyethylene, Dacron and UHMWPE (Honeywell's Spectra or Dyneema). The most common type is monofilament, made of a single strand. Fishermen often use monofilament because of its buoyant characteristics and its ability to stretch under load. The line stretch has advantages, such as damping the force when setting the hook and when fighting strong fish. On very far distances the damping may become a disadvantage. Recently, other alternatives to standard nylon monofilament lines have been introduced made of copolymers or fluorocarbon, or a combination of the two materials. Fluorocarbon fishing line is made of the fluoropolymer PVDF and it is valued for its refractive index, which is similar to that of water, making it less visible to fish. Fluorocarbon is also a denser material, and therefore, is not nearly as buoyant as monofilament. Anglers often utilize fluorocarbon when they need their baits to stay closer to the bottom without the use of heavy sinkers. There are also braided fishing lines, cofilament and thermally fused lines, also known as "superlines" for their small diameter, lack of stretch, and great strength relative to standard nylon monofilament lines. Braided, thermally fused, and chemically fused varieties of "superlines" are now readily available.
Fly lines consist of a tough braided or monofilament core, wrapped in a thick waterproof plastic sheath, often of polyvinyl chloride (PVC). In the case of floating fly lines, the PVC sheath is usually embedded with many "microballoons", or air bubbles, and may also be impregnated with silicone or other lubricants to give buoyancy and reduce wear. In order to fill up the reel spool and ensure an adequate reserve in case of a run by a powerful fish, fly lines are usually attached to a secondary line at the butt section, called backing. Fly line backing is usually composed of braided dacron or gelspun monofilaments. All fly lines are equipped with a leader of monofilament or fluorocarbon fishing line, usually (but not always) tapered in diameter, and referred to by the "X-size" (0X, 2X, 4X, etc.) of its final tip section, or tippet. Tippet size is usually between 0X and 8X, where 0X is the thickest diameter, and 8X is the thinnest. There are exceptions to this, and tippet sizes do exist outside of the 0X–8X parameter.
Tenkara lines are special lines used for the fixed-line fishing method of tenkara. Traditionally these are furled lines the same length as the tenkara rod. Although original to Japan, these lines are similar to the British tradition of furled leader. They consist of several strands being twisted together in decreasing numbers toward the tip of the line, thus creating a taper that allows the line to cast the fly. It serves the same purpose as the fly-line, to propel a fly forward. They may be tied of various materials, but most commonly are made of monofilament.
Wire lines are frequently used as leaders to prevent the fishing line from being severed by toothy fish. Usually braided from several metal strands, wire lines may be made of stainless steel, titanium, or a combination of metal alloys coated with plastic.
Stainless-steel line leaders provide:
Titanium fishing leaders are actually titanium–nickel alloys that have several very important features:
Copper, monel and lead-core fishing lines are used as heavy trolling main lines, usually followed with fluorocarbon line near the lure or bait with fishing swivel between the lines. Due to their high density, these fishing lines sink rapidly in water and require less line for achieving desired trolling depth. On the other hand, these lines are relatively thick for desired strength, especially when compared with braided fishing lines and often require reels with larger spools.
See also: Plastic pollution
Discarded monofilament fishing line takes up to 600 years to decompose. There have been several types of biodegradable fishing lines developed to minimize the impact on the environment.