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Fly Fishing Under a Bright Moon Reveals True Colours

What if feathers exhibit colours trout find attractive, but are invisible to human eyes?

A short story on fishing in bright moonlight may help lead us into what colours trout see, and just what that has to do with the colours humans do not see in feathers.

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 a river mouth on Lake Taupo, New Zealand, 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.

Photo of Booby fly

Booby fly shown dry and wet. The wet shape is important, to gain the maximum lifelike movement.

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' (the current formed where a stream or river flows into a lake) was within casting distance.

Sealing the decision was the complete lack of other fishermen in the rip – all at home I surmised cursing the bright moon and cloudless skies .

I rigged up my rod with a fast sinking shooting-head to a one-metre leader with a white Booby fly . 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.

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The fish, a reasonably well-conditioned hen of around two and a little-bit kilos (5lb), 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 2kg (4lb) mark and maiden hens (female trout who have not yet spawned), but there were two bigger 'jacks' (male trout), and a really fit and fat hen of around 3kg (6lb), that got to be dinner.

As I wandered back to the cottage, I began to wonder where - and why - the generally held view that trout do not feed in shallow water in bright conditions 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.

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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 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 true colours exposed under ultra-violet light were truly remarkable. These were magnificent colours simply not available to human eyes, unless exposed by ultra-violet. Some seemingly dull, nondescript birds became creatures of magical hues.

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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 marvelous when photographed under ultraviolet light. Marvelous because we cannot see these colours without the aid of ultraviolet light.

Is there a possibility that fish can see colours that are outside our human range of visibility? We know fish can see ultra-violet light. Perhaps fish 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 lead 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 ultraviolet light. Perplexing indeed, my Dear Watson.

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.

hare and copper nymph

Since I wrote this article I have received a great deal of information from around the world. Here is some of it:

Max Garth's excellent articles on Sexy Loops, (incidentally a great site; especially on casting, for beginners to experts.) Ignore the silly site name.

Books: For those keenly interested in the subject here is a little light reading:

Scientific American Vol 246 1982 "Colour Vision in Fishes" by Joseph S Levine and Edward F. Mac Nichol, Jnr.
Light and Life in the Sea" 1990. Ed's P.J.Herring, A.K.Campbell, M. Whitfield, C.L.Maddock. Cambridge University Press with particular reference to Chapter 10 of that work, "The Colour Sensitivity and Vision of Fishes" by J.C Partridge
The ecology of the visual pigments of snappers (Lutjanidea) on the Great Barrier Reef J. N.Lythgoe, W.R.A. Muntz, J.C. Partridge, J. Shand, D. McB. Williams.
Specialisations of the telost visual system: adaptive diversity from shallow-water to deep sea Shaun P Collin 1997. From Adaptive Mechanics in the Ecology of Vision Kluwer Academic Publications Netherlands.
The Visual System of Fish Ed. Douglas Djamgoz 1990 Chapman Hall London.

wee wet fly


Article written by Tony Bishop


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