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Colour in the Fishes Eye
by Max Garth

"Fishes are the evolutionary solution to a number of mechanical, aural, optical, structural, electrical and other engineering problems relating to the environment in which they exist. They are complex organisms, or animals, and their sensory systems have evolved to provide the necessary functions to make the whole fish a viable entity in the watery environment".

Fundamentally and simply, light is a band of electromagnetic radiation to which the eye, whether it is human or some other species, is sensitive. This band of frequencies is called the "visible spectrum". The exact definition of light has been in dispute for many centuries with Newton, Fresnel, Foucault, and Maxwell offering different theories. Einstein put forward the "quantum theory" and regarded light as consisting of energy quanta called photons. Then of course we have Mr Bohr's idea that both electromagnetic wave and quantum theory, wave-particle duality, are needed to explain the phenomena of light. This should rightly apply to "ALL" Radio Frequency energy, not only light because light wavelengths, 600 to 400nm, are RF energy, a small part of the electromagnetic spectrum.

How we see

But regardless of all of the woffle about light, Einstein and whoever; light is what we see, and some animals, even fishes, do not see it as we do. Like they may not, do not, see colour. But, again, the fact that we have eyes sensitive to those radio frequencies that make up the so-called visible spectrum means that light exists, for us, or anything with eyes. Without our eyes to see it, and our brain to sort out the neurological signals, it would not be there, or we would not see it, and, to us, it would not exist. Very probably, neither would we but that is irrelevant to the argument.

It is a matter of "our world", that bit that affects us. Each of us sees the world, or our bit of it, differently. That is because each of us looks at it from a different angle, and place, and gets a different view. There is no other person on the planet with the view that you, or I, have. Simply because there is only one body in that particular place at that particular time. And what we do see is light photons reflected from all of the objects in our view. Each object is illuminated by the light photons transmitted from the source, and depending on the colour of the object, those photons are either absorbed or reflected, or retransmitted, until they arrive at the rods and cones in our eye. That electromagnetic radiation, those light photons, gives us that view. Because our eye recognises that it is there, counts the number arriving and passes the result to our brain, via the optic nerve. The calculations on what colours are there, are done in the brain, and we “see” the result.

The interpreter

Therefore vision is a matter for the brain, of humans and all of the other animals on this rock; and the lower the order of animal quite obviously the lower the order of vision: ie, the simpler the visual system the lower the resolution. If light is there we see it, and because it has a finite velocity, 300,000 metres/second, some time AFTER it was transmitted from the source. But until it arrives there is dark. Dark only occurs with the cessation of light and light causes the cessation of dark. Confused. Well rest easy, because it is obvious that we have to have dark, but dark isn't anything but no light or low light illumination, and your eyes are configured to see low light levels. Quite brilliant things eyes, and of course brains.

All of which means that light is only there because you have eyes designed to detect those little light photons, or whatever light is, and pass the messages along to your brain. It sorts out that neurological information and your head says, as was attributed to some other being, "let there be light, or is it sight, or both or …???"; and lo and of course behold, there is.

Of course that is purely anecdotal evidence. Nothing scientific there because as the man said, "it can be easily seen to be".


Colour vision is our visual systems sensitivity to light photons in the band of electromagnetic frequencies called the visible spectrum. It goes from red, orange, yellow, green, blue, indigo to violet. We do not see infrared or ultra violet but some of the fishes may see infrared and one species at least, the blue, or slimy, mackerel, does see ultra violet. The low frequencies, red light, have the longest wavelengths and the high frequencies, violet, have short wavelengths.

The retinal elements associated with colour vision, the cones, are colour sensitive, they have a drop of coloured pigment on the tip, and count the photons they capture and the brain sorts out the result. Colour is not in the eye but the brain. The fish may be trichromatic, and have three colour pigments or dichromatic and have two colour pigments. The retina of those fishes which can see colours will have the cones arranged in a matrix. This might be a blue sensitive cone surrounded by green and orange/yellow sensitive cones. Or it might be made up of only two colour sensitive cones, blue and green; in which case it will be a blue sensitive cone surrounded by green sensitive cones.

We and the fishes have an adaptive eye that is sensitive to the illumination level. If the light level is low or photon limited, there is no colour vision. The brightness of the colour or brilliance depends on the illumination. If the illumination is high the colour is light and bright. If it is low the colour is dark. We and the fishes need at least two colour sensors before the brain can discriminate colour hue or difference.

Shades of grey

The other elements in the eye, the rods are for grey scale vision and merely count photons regardless of colour. They only provide information on the brightness of objects. In other words the lighter and brighter the colour the greater the number of photons reflected and counted. Conversely the darker the colour the less the numbers of photons reflected and counted. Of course this will vary depending on the spectral illumination.

In Humans the retina contains both rods and cones and to allow for changing illumination and the need to see in both colour and grey scale the rods, the most sensitive, each has a drop of Visual Purple, or Rhodopsin, on the tip. In bright illumination this bleaches de-sensitising the rod and protecting it from the bright light. As the illumination degrades the visual purple is re-generated by vitamin A and allows the rod to detect very low-level light photons. The lack of vitamin A in the body can lead to "night blindness" or a low level of grey scale vision.

In fishes eyes the rods are physically retractable. And when light levels are high the rods are retracted into the back of the retina and covered with a black melanin layer. When light levels fall and the cone sensitivity degrades the rods move upwards to lie alongside the cones to provide grey scale vision.

Enhanced brightness

Some fishes have a Tapetum lucidum, a reflective eye, similar to nocturnal animals. The Tapetum is a layer of reflective crystals or some other reflective system on the retina to reflect light which has already passed the rods, back for a second chance at detection. There is a very slight delay in this system and the sight is very slightly blurred. But it is very sensitive. The Tapetum can be fixed, Choroidal, for fishes without colour vision or Retinal, retractive with the rods so that it only operates in photon-limited conditions.

Fishes with Tapetum lucidum include barramundi, tragelin and mulloway. The fact that these species have a reflective eye creates problems when fish are removed from photon limited water conditions and/or flashed with cameras. They can be heavily light shocked and become disoriented which does not help their survival on release in crocodile infested waterways.

Humans, who are only one species, and who can see all of the colours of the spectrum have a trichromatic visual system. They have blue, green and yellow/orange sensitive cones in their eyes. Generally, at least as far as is known, a lot of the 25,000 species of fish do not have a red sensitive cone in their eye. These fishes are dichromatic while some, the deep-water species, are monochromatic.

Water is a colour filter

To understand the view of these fishes, one has to firstly understand that water is a colour filter, depending on the particle content and it will effect the transmission of colours. The colour of the water, as seen by our eyes, blue, green or dirty is an indicator on the particle content and the light transmission. Secondly water is about 800 times denser than our atmosphere and light photons are scattered and absorbed by their interaction with water molecules and suspended particles. Thirdly a fish has evolved to fit into a particular niche in the underwater environment. Its visual system will match that niche exactly. It will have colour vision, even three colour vision, if it needs it. If it doesn't it will not.

The view one has of objects underwater is only light photons passing through the surface illuminating and being reflected by the object we are looking at. Those photons are scattered and absorbed which reduces the number striking the sensitive cones in the viewing eye. This reduces the intensity of the image, adds a misty light from scattered photons from other sources and generally distorts the view. The longer the viewing path the greater the effect. The deeper in the water and the further away the harder it is to see, for us, as well as the fish.

From pink to blue to grey

I guess people understand that pink is bright violet, but as we see it, as do the fishes, it ends up as basically blue and red. If the fish doesn't see red, that pink, bright violet, turns into bright blue which the fish sees as a very light shade of grey. Make it fluorescent and it is still the same. The fish only sees the blue photons so it cannot really discriminate it as anything else but a bright, light shape. I know that because I looked at a pink flower through a blue filter. You should try that.

This pink into blue underwater is what makes Rod Harrison's Bionic Braid Salt Water Fly backing line practically invisible to the pelagic fishes, most of which are blue/green dichromats, yet it is brightly visible to the angler. The line is extremely bright, high luminosity, and as far as the fish is concerned is very light grey which melds into the underwater "space light" conditions.

Contrast or colour?

If the colour is dark, which absorbs a lot of the available light photons, the fish sees it as a black hole in the visual field. Dark colours like black, deep blue, deep green provide contrast but no colour. Flashy Profile Flies, dark reflective colours, reds/blues/greens are, to a dichromatic fish, like tuna, mackerel, marlin with blue/green visual system, a blob of contrast with internal flash. Not that it's a problem but it works, because the dichromatic fish doesn't see those dark colours as anything but contrast. Of course that's how it sees small forage fish anyway.

Any colour, no matter what, seen against the water surface is black to the fish. The background is intensely bright light from overhead and obviously the object is casting a shadow, is not illuminated from underneath to any degree, and appears as black. Mind you contrast is what most pelagic fish look for, because most feed from deep in the water column and hence their visual systems dictate that feeding method.

One should realise that what you see is the result of a trichromatic visual system, which can discriminate all of the colours and hues, as well as subtle colour differences. The fishes may not be able to do that, and the fact that you can, quite simply does not mean they can.

On the other hand the ocean, or any other body of water, is, depending on the particle content, a colour filter. The colour of the water, as it appears to you, looking at it from the shore, is indicative of the colour filter active at that time. If the water is clear blue, the water has very little particle content and represents a blue filter. Most of the other colours are attenuated at shallow depths. If the water appears green, it is a green filter and the predominant colour in that water is green. If it is brown the water is a red/orange colour filter and the predominant colours are red/orange. In very thin mud, the filter is red or even infra/red.

Light and depth

The spectral illumination, that is the light level, depends on the water colour, because it denotes the particle contend and the depth of photon penetration. The darker the colour the less the illumination. And, the lower the illumination level, the darker colours appear both to you and to the fish, and objects lose their shape and form. In clear blue water an object might be visible for 100 metres. In green water that same object might disappear at 50 metres and in brown water at 5 metres. In blue water light penetration exceeds 400 metres, in green water, 150 metres, in brown water, maybe 1.5 metres.

Visual distance depends of the amount of particle content because it determines the level of light photon scattering and absorption between the viewing fish, or person and the object itself. The object fades and loses its shape and eventually disappears into the space light, that background colour of the water.

One of the effects relating to surface conditions is grating light. As the light photons penetrate the surface and enter the water, the penetration angle is dependant of the water surface conditions at the time. Therefore the light passes into the water surface in beams and these beams can illuminate objects, and fish with distinct bars. Some fishes are barred in colour and if they are swimming near the surface the bars, melding with the light beams, allow the body shape to become indistinct. If the fish is at depth the bars tend to cause it to flash as the light beams vary in relation to the surface conditions.

It would probably be remiss for me to say that what you see, of lures, is what you get but what the fishes see of some lures is a difficult question to answer. White and black barred lures work like dreams under the surface but not so well right on the surface. This is because of grating light effects. Deep running lures should be shiny white and easy on the eyes. With synthetic materials the best are the flashy white ones, silver and in dirty water gold. Or straight out flashy-black materials such as Crystal Flash or Flashabou are the most visible and fit the oceanic system better than others.

Lures and flies

The best lure for general tropical fishing is a white bucktail jig, or those flashy plastic ones they have these days. The reason, they cost $2.50 each and catch fish like all hell let loose. Everything in the tropics eats them with absolute gusto. You can spin them at supersonic speeds, you can jig them or troll them and you will lose them in droves. Better to lose a $2.50 lure than a $20.50 lure.

The best fly for general fly fishing in the salt is a Lefty's Deceiver in fluorescent white. I know that Lefty's Deceiver pattern is regarded as a “style” of fly, I know that Lefty himself thinks that is the case, but to my mind Deceiver flies are not really a "style". It is a specific and quite definite pattern with only one recipe and is streets ahead of any other fly in the salt. You can catch anything from bream to bill-fish on Deceivers. The reason it is the best is because it has caught more fish, and more species of fish than any other single pattern, bucktail or otherwise. It's been around since 1962 and it still out fishes the best of the rest. If you wandered around the world fishing in any waterway in any country you would only need to take a shoebox full of white Deceivers of a number of sizes. You would catch a lot of fish.

There may be variations but few, if any, present the same action, and, what is most important the brightness, and tail flutter of the standard fly.

When it comes to flies I believe that tying flies is an art form. But, even so, the result of any fly tying exercise, whether it is tied for fresh or salt water; is, or should be, a fish.

Max Garth has been saltwater flyfishing Australian long before it was possible. Inventor of the term "hucking" (to cast a flyline, much like a brick, whilst standing on a rock), I get the impression that there's not much Max hasn't tried. He lives and fishes West Australia, where I hope to meet him on my travels.


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