[oucorry]

Making Sense of Carp
By Steve Lightfoot



Like any good hunter the angler should have a basic working knowledge of their prey. Understanding how a fish uses its senses to feed and evade danger is, of course, vital if we are to understand just why it is they will or won’t pick up our baited hooks. In this short introduction I won’t be drawing any conclusions on how exactly this knowledge will put more fish on the bank for you – the implications are too many and varied on the issues regarding how carp feed, especially regarding how carp react to different coloured baits and flavours, to cover in one whole edition of a magazine let alone a short article. Instead let’s just have a look at how a carp’s senses work.

Smell

A carp’s sense of smell comes through a set of nostrils (called ‘Nares’) located just in front of the eye on either side of the head. The water is channelled through the nostrils by a raised flap of skin in the middle of each Nare and down through a set of thousands of miniscule hairs which can distinguish between sweet, sour, savoury and saline substances. These sensory cells are extremely sensitive, giving the fish a far more acute sense of smell than a human. The fish is trying to detect low levels of chemicals (such as amino acids) that its natural prey such as bloodworm, crustaceans etc. emit into the water. When you consider the carp can detect bloodworm in several inches of silt you can see just how acute it’s sense of smell is. Smell is used by the carp essentially as a long range detection mechanism. As the fish comes closer to the source of the smell the taste buds kick in to action.

Taste


Just like humans carp have a sense of taste via a set of taste buds. However this is where the similarity ends. Like its sense of smell, the carp also have a highly developed sense of taste. In the first place it is important to remember the old maxim that ‘carp don’t have hands’ therefore the carp acts almost like a vacuum cleaner when feeding, using its sense of taste to reject items that it does not want to eat. Furthermore a carp’s taste buds are not just located inside the mouth; carp have taste buds on its barbules, pectoral and pelvic fins, underneath the head and even have a small number of taste buds located along the side of the body. These external sensors allow the carp to more accurately pinpoint the sources of food. Thus the carp smells the bloodworm in a silt bed, swims over the silt and then pinpoints the area within the silt that holds the bloodworm. This silt, along with other detritus, is sucked into the mouth. At this stage the main taste organ on the top of its mouth, the ‘Palatal Organ’, comes into play and traps the food against the bottom of the mouth, with waste such as silt and sand being blown out through the gills. Larger waste items are spat out through the mouth. All this happens in seconds, and it’s estimated that about 97% of what the fish takes into its mouth is ejected. Carp will also clean food items by spitting them out to rinse them and taking it back in. Accepted food items are then passed back to be crushed by the set of pad like teeth at the back of the mouth (the ‘Pharyngeal Teeth.’)

Sight

While we can never quite be sure exactly what a carp sees, its eyes are able to operate in much lower light levels than our own and can also detect a wide spectrum of colours. The position of the eyes on both sides of the head give them a good sideways field of vision, in fact almost 360 degrees ( apart from near the tail ). Above the water their forward vision is quite sensitive to changes in light and movement, so when stalking carp use slow movements, avoid standing out on the skyline and try to blend in with your surroundings ( hence the use of camo clothing! ) Better still approach them from behind. Research has suggested that carp have a total circular window of vision above them of around 97.6 degrees (48.8 degrees on either side of the body from a line drawn vertically through the fish). Outside of this window it’s suggested the carp sees reflections of the bottom of the lake with the water surface acting as a mirror. The eye position also has implications for feeding since carp cannot see items immediately in front of and below their mouths, when it relies on the barbuls’ sense of touch and taste to detect items. A few inches and beyond in front of the mouth however is where the carp’s sense of sight is most acute since it can focus on items using both eyes. Each individual eye can also see reasonably well on both sides of its body round to a few inches either side of the tail.

Hearing

Carp do not have a visible set of ears; rather they are inside of the carp’s body on either side of the head just above the gills. These ears, located at the rear of the brain, consist basically of a fluid filled sac that contains set of tiny hairs on an ear bone (the ‘Otolith’) which detect vibrations in the water outside. The ears are also conncted via a set of bones to the swim bladder, which acts as an amplifier, so all in all the carp has a highly effective aural detection system capable of detecting frequencies from 60 to 6,000 Hz.

Lateral line


Like all fish the carp has a pair of lateral lines the run down the sides of its body. The lateral line is a canal filled with fluid dotted along its length with miniscule openings. Inside this canal are sensory cells called ‘Cupula’, which are jelly like structures with fine hairs branching out of them. These allow the carp to detect water flow direction, vibrations and changes in pressure.

Clearly then a carp has a highly developed set of tools that allow it to survive and flourish. The one conclusion I will draw is that obviously we need to be well aware of just how sensitive a carp is to noise and vibration. I’m forever amazed here when I see anglers using mallets to bang in tent pegs and bank sticks, though less amazed when they complain about how badly the place is fishing! Sound travels alarmingly well under water, so keeping noise and vibrations to a minimum is going to help.