I’ve always been interested in understanding how fish, particularly trout, perceive the world around them. With this interest I’ve often researched studies around trout vision, largely focusing on the topic of colour. There are so many angler held theories on what colours trout see and an even wider range of theories on the topic of UV vision in trout.
I spent hours on the internet researching these topics, seeking clarity beyond theories, I wanted more than “apparently” and “I’ve heard”. One thing I began to notice as I searched for these answers, while many anglers only had theories, one man had answers…well studied peer-reviewed answers. Any information of substance and credibility on the topic seemed to have his name behind it. Knowing this to be the case I sought out his work and studies that he has published and read what was available and relevant to the topic. The Professor behind these studies was Prof. Inigo Novales Flamarique.
Prof. Inigo Novales Flamarique is a Professor at Simon Fraser University in BC, Canada. Some of his areas of expertise include neuroanatomy and physiology of fish visual pathways as well as detection and processing of colour and the polarization of light.
While I meticulously read through his studies and took a number of important lessons I had further questions to ask, maybe due to the fact that I’m less scientifically literate than a…well…scientist. Or maybe due to the fact that these studies aren’t exactly tailored for the angling community meaning I had to sift through what was relevant to anglers (still quite a lot to be fair). What better way to find this out than to contact the Professor himself. I didn’t expect much back but I received a reply and was given the opportunity to have those extra questions answered.
Below is the written interview I had with Dr Inigo Novales Flamarique:
When findings such as yours in your studies on species such as Rainbow Trout (Oncorhynchus Mykiss) come to light, do these findings necessarily apply to all subspecies of Rainbow Trout? Or on the other hand, does it work the other way and often apply to the family of which the species belongs?
What other colours do trout and other salmonids see? Is it similar to our range and is it possible for us to imagine the colours that they see? Do any particular colours stand out more than others?
What does the UV cone when present do? Does the fish see the world through the vision of a blacklight or do they simply see an extra colour (ultra-violet) within their spectrum?
The UV cone adds sensitivity to wavelengths below 400 nm. The UV, like the blue cone, feeds into retinal circuitry that opposes the green and red cone inputs. Thus, anything that reflects in the UV would be seen as positive contrast against a green or red background. I have never seen what a blacklight does but I am assuming that you are seeing the reflection from an object illuminated with UV light. If so, and if it is perceived by humans (which cannot see much below 380 nm, because of lack of lens transmittance), then the fish equipped with UV cones would see the same reflection much brighter (because the lens lets light through to 320 nm). But, of course, the intensity of the reflectance perceived would depend on the background light surrounding the object being illuminated. Shining a light on a fly that reflects in the UV in a dark room does not have much meaning if the trout is not swimming in total darkness and the fisherman is not shining a UV light on the fly.
What does all this mean for fly fisherman?
Amongst all this science talk is some fairly relevant and important information that we can take as anglers. Also, it allows us to take this information on a factual basis rather than a “I’ve heard” and “Jeff down the road reckons” basis (sorry Jeff). It comes from a man with a PhD on the topic who has spent much of his life studying the fish we pursue who also has published many peer-reviewed articles that have become particularly important to others studying or trying to understand vision in animals.
In my opinion, the key points of relevance here are:
- Key results from studying one species of salmonid vision are relevant across the entire salmonid family (i.e a brown trout vision will not be significantly different to that of a rainbow trout)
- No more guessing what colours are visible to a trout. The visible colour spectrum of a trout from is 320nm to 740nm as illustrated in the diagram above. However, it has been found from Dr Flamarique’s studies that trout lose this UV sensitivity as they progress through life.
- We may be giving trout/salmonids more credit than they deserve for in regard to the detail they are capable of seeing (visual acuity). This explains however why size and profile (silhouette) are often more important when fly tying than tiny details.
- The salmonid/trout visible colour spectrum is not too different from our own. The main difference being the visibility of light between 320nm and 380nm at particular stages during the life of a trout.
- The colour that will stand out the most in a salmonids field of vision (against the green background) is blue. I believe this could be important when fishing for species such as sea trout and salmon when we are largely trying to illicit a territorial reaction rather than perfectly imitate a food source.
Comment below or on Facebook what you learnt these insights and I would love to hear how you believe this information can be used by anglers. I will leave at the bottom some studies from Prof. Novales Flamarique relevant to the topic.
List of Studies