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We know fish see colours in different ways to humans, but can they see colours we can not?

© 1999 Fish with Bish
Blue Moon

It was, as usual, a bright moonlit night on Easter Sunday night. Should not have been any surprise – the state of the moon is one factor that sets the date of Easter. Something of a surprise was the fact that I was out fishing the river mouth at all. Usually I would buy into the generally held view that fishing for trout under a bright moon is pretty much a waste of time.

But I had not been fishing for a week or two, and the mirror calm conditions were just too good to ignore. Even more difficult to ignore was the fact that the rip was flowing almost parallel to the beach. Totally impossible to ignore was the fact that end of the rip was within casting distance. Sealing the decision was the complete lack of other fishermen in the rip – all at home cursing the bright moon and cloudless skies I surmised.

I rigged up my rod with a fast sinking shooting-head to a one-metre leader with a white Booby. At about 10pm I wandered down to the river mouth, walked the hundred metres, or so along the beach to the end of the rip, then waded out to mid-thigh depth.

Somehow I dropped my first cast right where it should, and I felt the line tighten as it sunk through the dying current out there where the rip died. I gave the line a twitch or two and then let it sit. Twitched again, let it sit, still nothing. About ten minutes of casting and retrieving produced absolutely nothing. I was starting to doubt my reasons for fishing on such a bright night when some small clouds darkened the light from the moon. Quickly I tied on a small dark Booby with a lumo body to the bend of the white booby’s hook, and ‘lit’ it up with my torch. But by the time I had changed my rig the small clouds had moved on.

My laziness took over and rather than take off the lumo Booby, out went my new tandem rig. I gave it time to sink and gave the line a twitch, nothing. I was just about to twitch the fly again when I felt a distinct ‘tap’ on one of the flies. Then nothing. Another twitch – still nothing. Another twitch and the line pulled back against my line hand.

The fish, a reasonably well conditioned hen of around two and a little-bit kilos, was soon landed and then swimming away minus the lumo Booby’s hook, with a ‘what the hell was that’ look on its face.

That fish was the first of around nine fish I caught in the next hour and three-quarters – the action only curtailed by the midnight fishing curfew in force at Taupo. Most of the fish were around the 2-kilo mark and maiden hens, but there were two bigger jacks, and a really fit and fat hen of around 3-kilos, that got a knock on the noggin.

As I wandered back to our cottage, I began to wonder where – and why – the generally held view that trout do not feed in shallow water came from.

The most often quoted ‘reason’ seems to be that baitfish such as smelt, so important in many of the central North Island lakes trout’s diet do not come into the shallows during bright moonlit nights. No feed – no predators is a pretty compelling argument.

Well it should be a compelling argument but for the fact that I have seen, as I did last Easter Sunday night, heaps of smelt in the shallows on moonlit nights. And if smelt do not like the light, why are they in the shallows on bright sunlit days? Sight fishing for smelting trout on shallow beaches around Taupo is one of my favourite occupations, especially on bright sunny days.

But fact is, and my diary confirms it, I have not consistently caught fish on moonlit nights.

The seasonal pre-spawning congregations of fish around river mouths may have explained my success that night. A possible explanation – but unlikely. It was too early, and none of the hens were in or apparently anywhere near spawning condition. There had to be something else.

It was then that I remembered that all the fish I caught except one were taken on the lumo Booby. This despite the fact that – to my eyes at least – the luminescence of the fly died in the bright moonlight in only a few seconds after being lit up by my torch. The depth of water I was fishing in was only two or three metres, so there would be little difference in light at the surface or below.

I also recalled that I rarely, if ever, used lumo flies on bright nights prior to this night. I usually used bright flies, as do, and did most other anglers I have fished with.

Then I remembered watching on Easter Saturday night a nature program on birds. The programme contained a fascinating segment on the fact that birds can see colours that are invisible to human eyes. The shots of bird’s colours exposed under infrared light were truly remarkable. These were magnificent colours simply not available to human eyes, unless exposed by infrared. Some seemingly dull, nondescript birds became things of magical hues.

Here is food for thought. Fish eyes are in many respects similar to bird eyes. Some fish exhibit ‘luminescent’ colours that are visible to human eyes. ‘Lit-up’ marlin and kingfish exhibit these colours. Fresh out of the water snapper also show bright luminescent blue spots. Squid are rightly famous for their ability to undergo rapid changes of colour – changes made even more marvellous when photographed under infrared light. Marvellous because we cannot see these colours without the aid of infrared light.

Is there a possibility that fish can see colours that are outside our human range of visibility? Perhaps fish can see luminescent flies differently to us. This may go some way to explaining why luminescent skirts on marlin lures fished during the day are reported to be so successful.

It may also explain why trout seem to grab lumo flies, when to our eyes, there is no luminescent prey in our fresh water fisheries – and take lumo flies on bright nights when to our eyes the flies do not ‘glow’ for any length of time.

Here is another question my train of thought was leading me to ask. It has generally been held that tying flies with bird feathers was because feathers moving in water imitate the action of creatures that live under water and are fed on by trout.

But maybe we have been missing something? What if the imitative movement was not the only reason that trout are attracted to flies incorporating feathers? What if the feathers exhibit colours that trout find attractive, but are invisible to human eyes? Can fish see the hidden colours in feathers that birds can see, but we can not without exposing the feathers to infrared light. Perplexing indeed, my Dear Watson.

I have, since Easter, searched the Net, and through my collection of fishy books, but can find no research or information on this subject. If anyone can point me in the right direction, I would love to hear from him or her.

Meantime, I will be less easily persuaded to remain sitting in front of TV on moonlit nights. I will be out there with my lumo flies, because if nothing else I believe that there is only one good time to go fishing – and that is any time I can.

Further articles:
Night fishing I
Night Fishing II
Sight Fishing Smelting Trout