Do fish see UV?

Darwin’s theory states, in part, that if a biological function is not used, function becomes a burden and will be lost.

This means a species of fish with no use for eyes will slowly lose them over time.

We know many deepwater fish species (bluenose for example) have large eyes and live in very deep water, where there is a very little or even no visible light. Why then, do these fish have eyes? Researchers are discovering that some fish seem to be able to see UV light, which penetrates much further into the water than visible light. If this is the case, it may explain why deepwater species have kept their eyes.

UV light is short wavelength, high-frequency energy, mostly from the sun, invisible to us, but visible to some of the fish species scientists have tested so far.

UV light from the sun arrives in the form of the rays that can also cause sunburn and damage to your skin. It is a powerful form of light, especially here in New Zealand, where the hole in the ozone layer above our country is thought to be responsible for the high UV levels present.

Visible light from the sun is not good at penetrating into the depths. Depending on surface conditions, some light is reflected away at the water surface, with more turbulence meaning more reflection. Beneath the surface, light may be scattered or absorbed by solid particles such as plankton or sediment. As a rough rule of thumb, by 10m down in inshore waters, only 20% of the original surface light is still visible. At 150m, there is hardly any visible light available for fish to see (except for that generated by light-emitting organisms) by human standards. However, UV light can penetrate much deeper than visible light – up to 700m deep in ideal conditions.

So if the fish you’re hoping to catch can see UV light (the research has yet to be done on NZ fish but it seems likely they can), it makes sense to have UV-reflective paint on your lure so it’s more visible to any UV-seeing fish, potentially enabling more fish to be caught. Better still, there are now UV-reflective paints designed to be used on fishing lures.

However, keep in mind that this quality isn’t necessarily restricted to deep water; any fish capable of seeing UV light will also see it in shallow water or at the ocean’s surface. It therefore makes sense to have UV reflective paint on lures fished at any depth. In fact, there was quite a bit of discussion about using UV reflective paint on lures and baits at the recent ICAST fishing trade show in the USA, and there were even a few gamefishermen playing around with UV reflection on their trolling lures.

As one of the hottest topics around right now, several companies are exploring the potential of UV-reflective coatings, and there are already some lures utilising UV-reflective paint available overseas. Results in testing and on-the-water use are reportedly very positive.

Although New Zealand fish such as snapper, blue cod, kingfish and hapuku have yet to be tested for visual UV sensitivity, to me, using UV-reflective paint is a very exciting concept, especially as anything that may give you an edge has to be worth trying. It’s certainly something I will be trying on the lures I manufacture – it could well be the next big thing…

Paul Senior co-owns Pacific Ocean Distributors, manufacturers of Cyclops Lure heads.

	This article is reproduced with permission of New Zealand Fishing News 2010 - by Paul Senior Re-publishing elsewhere is prohibited