This is the first in what may become an occasional series of angling myths. Basically bits of information doing the rounds, based on either nothing at all, pure speculation, or on incomplete and inaccurate data. All with the tag "in my opinion" of course.
So: number one. "Fish cannot see red fishing line".
This was doing the rounds a while ago, and still persists to an extent, mainly in some river fishing, barbel forums and probably elsewhere. At least a couple of very successful anglers were touting this about, and using red braid on their reels. Practising what they preached of course, but did they have any basis for their thinking? Well, sort of, but with some very inaccurately applied science.
The colour red is absorbed more readily by water, becoming less and less intense as the water depth increases, and this effect can be seen quite clearly in all those underwater sea videos, where, unless the camera shot is close to the subject the whole scene looks bluish. It is bluish because the red end of the spectrum has been greatly absorbed compared to the blue end. To get reef fish photographs in true colour it is often necessary to add artificial light before clicking the shutter.
So what happens with red line? In shallow water, seen at close range by the fish, it remains red, limited absorption of any colour taking place. At great distances and depths the red component of the line would no longer be visible, BUT the line would then look to be black. Absence of red light does not mean that the line would then become invisible. It simply means that there is no red light available to be reflected from the line. If red light is the only colour to be reflected from that line in air, then in deep water, little red light remains to be reflected from the line. Any object emitting or reflecting no light, or very little light, appears as black.
The only way to make line invisible in water is to make it from a clear, transparent and colourless material. And then, additionally, to use a material that has, as far as is possible, the same refractive index as water. Under those circumstances, light rays pass straight through the line, without being bent as they pass through the line. In effect the line then appears not to be there. And that is exactly what some modern lines try to do. They try to eliminate the "bent stick" effect that you can easily see when you penetrate a water surface with a straight rod. The rod appears bent, because the refractive index of air is different to that of water. The objective therefore is to create a line without any of that bent stick effect. I understand lines which get near to this are called Fluorocarbons. Such lines have their limitations, I am informed that they are usually stiffer than conventional lines, and there is little advantage to use them as floating lines, because the meniscus effect will still allow them to be seen.
To those who might still subscribe to the invisible red line theory, I would say: "Take your red line, put it into the river. Can YOU still see it? Of course you can, and so can the fish."