Understanding the biology and behaviour of the fish we hunt is an important part of the process of becoming a consistently successful angler. The more we know about our targets, the easier it is to fool them into biting or striking our offerings. A big part of this understanding involves having some idea of how a fish’s senses work.
Just like humans and most other vertebrate (back-boned) animals, the majority of fish species have a well-tuned set of senses that allow them to monitor their surroundings, find food, locate spawning partners and react to various other external stimuli. Like us, most fish can see, hear, smell, taste and touch. However, in addition to those five basic senses, many fish species also have at least one and sometimes two extra senses that are related to the detection of vibration and, in at least a few cases, weak electrical fields.
When it comes to designing truly effective clothing and accessories for anglers, the most important consideration in my opinion (after the comfort and functionality of that clothing, of course) is reducing our visibility to the fish. With this in mind, let’s take a closer look at what fish actually see:
THE EYES HAVE IT
To better understand how fish see their world, we first need to consider the general concept of sight in animals (including humans):
The visual system in humans and many other animals allows individuals to assimilate information from their surroundings. The sense of sight begins when the lens of the eye focuses an image of its surroundings onto a light-sensitive membrane in the back of the eye called the retina. The lens of the eye focuses light onto photoreceptive cells within this retina. These cells detect photons of light and respond by producing neural impulses or signals. Those signals are in turn processed by different parts of the brain, creating a mental image or picture of the world.
Of course, for sight to work, light is needed to illuminate the creature’s surroundings, and to generate the photons that stimulate those cells in the retina. This light bounces off objects and it’s these reflections of visible light that define the shape, size and texture of various objects.
The fish that anglers hunt generally have excellent eyesight and can detect a broad range of colours; both beneath and above the water.
Detecting objects by seeing the light they reflect is only half the picture, if you’ll pardon the pun. Discriminating between colours is also crucial for many animals, whether they’re identifying food and predators, finding their way, or seeking out potential mates for breeding.
COLOUR MY WORLD
Colour vision is not as straightforward as it might seem. The ability of any organism to distinguish colour is based on the wavelengths or frequencies of light reflected or emitted by particular objects, and these can vary depending upon the colour (wavelength) of the light source itself.
The “white light” provided by direct sunlight contains a mix of the entire light spectrum (including those wavelengths visible to us, as well as longer or shorter wavelengths not detected by our eyes). However, it’s worth remembering that perception of colour is a rather subjective process. In other words, different people (and different animals) may well see the same illuminated object in completely different ways.
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RODS & CONES
Animals with backbones, including fish, differentiate between colours by using cells in their eye called “cones”. Different sets of cells called “rods” are responsible for the detection of black and white images (especially in low light conditions). The majority of humans have three different types of colour-sensitive cones in their eyes. As a result, our visual experience is referred to as “trichomic colour vision”.
Interestingly, many types of fish, birds and even insects are well ahead of us in terms of colour vision. Some of these creatures have four different types of cones instead of just three, and a few also have a lot more cones than us. For example, you might be surprised to learn that farmyard chickens have twice the number of colour-detecting cones as humans! As the number of these cones increases, so does the creature’s ability to make finer and finer discriminations between colours. So, it’s highly likely that a humble chicken can far more easily differentiate between, say, the yellow of a corn kernel and the yellow of a dandelion flower than we can! Perhaps this visual adaptation aids chickens in their constant search for food.
Just as in chickens, the eyes of fish have also evolved to better accomplish varying tasks. For example, fish that feed predominately near the surface or in shallower, clearer water, especially during daylight hours, will often have more cone cells than rods, as colour vision gives these fish a distinct advantage under such well-lit conditions.
By contrast, fish that feed primarily at night, in dirty water, or at great depth will typically have more rods than cones, as rods are more sensitive to low light levels. This adaptation allows these fish to make better use of the limited available light coming from sources such as the moon or bioluminescence (organisms that create their own light), but also means they are less able to see a wide range of colours.
LOW LIGHT SPECIALISTS
Some species have taken these low-light adaptations a step further by developing a special reflective layer at the back of the eye called a “tapetum”. This mirror-like membrane reflects light that has already passed through the eye back into the retina, giving the photons a second chance of being detected and greatly enhancing the fish’s ability to see in very low light or murky water. It’s this reflective tapetum in the back of a barramundi’s eyes that causes the distinctive red or pink glow so often seen in flash photos of this popular species.
As already mentioned, in dirty water or low light, fish rely much more heavily on their sensitive rod cells than their colour-detecting cones. As a result, they are most likely seeing their world in shapes and silhouettes consisting of various shades of grey rather than in colour.
As light levels and water clarity change, many popular angling targets have the ability to switch their reliance from cones to rods, and vice versa. However, this changeover process is thought to take some time (possibly as long as an hour), and this may help to explain why many species are more susceptible to being fooled by our lures during the so-called “change of light” periods around dawn and dusk. It’s also likely that some predators have adapted to change their reliance on cones or rods faster than their prey, thus giving them a distinct hunting edge at this time of day.
So what do fish actually see? According to fisheries biologist Thomas Boyd, science can’t yet answer this question with much certainty. The majority of research in this area involves monitoring the rsponses of fish to particular timuli, such as different colours. Applying the test results from such experiments performed in the lab’ to practical fishing scenarios can be tricky.
However, we can definitely assume that most of the fish we chase in coastal waters, bays, estuaries and freshwater environments, as well as all those pelagic fish that hunt in the surface layers further from shore, rely heavily on sight to detect and track their prey, as well as to avoid potential enemies, and that almost all of them can differentiate between Many fish have excellent vision and see a broad range of colours.
colours when the water is reasonably clear and light levels are high. As an example, sight in marlin has specifically adapted to a clear water environment with lots of light. A marlin’s, eyes are effectively split into two sections: The part of the eye that faces upwards contains more colour photoreceptors (cones), while the part that faces down contains more photoreceptors that are sensitive to light (rods). Furthermore, as much as 30 per cent of a marlin’s brain is dedicated to processing and interpreting vision. This fact alone indicates just how important sight is to these billfish (and to many other pelagic predators, which also devote a lot of brain space to the sense of sight).
We also know that lots of fish, including species as diverse as carp, slimy mackerel, brown trout and damselfish (to name just a few), can see light reflected off objects at the ultra-violet end of the spectrum: wavelengths which are invisible to our human eyes. This allows them to see patterns and shapes we could never hope to identify, and also to detect UV-reflective objects at greater depth or distance through the water.
It’s also been identified that other fish (including bait species such as anchovies) can see “polarised” light, which is mostly encountered early and late in the day, or in the reflections given off by the very silvery scales of these fish themselves (and possibly by some of the predators that hunt them).
DON’T BE SEEN!
We still have an awful lot to learn about the way fish see and interpret their watery domain, but we can be reasonably certain that most of the species we hunt — especially in clearer, shallower waters — have good to excellent eyesight, can perceive a broad range of colours and tones under the right conditions, and that many can see light reflected at wavelengths that are invisible to us (such as ultra-violet)...
In clearer, shallower scenarios, fish can also detect objects, shapes and movement beyond the water’s surface, which means they can see us if we don’t wear clothing intended to blend in with our surroundings and break up our shape and outline… That’s exactly where Starlo’s Finesse Fishing Wear comes in!
In future blogs we’ll look in much more detail at the fascinating subject of attempting to remain undetected while hunting fish. Until then, Tight Lines!.