HOW FISH COMMUNICATE

The fundamental ability to communicate is something we take for granted and is a skill that is common throughout higher animals. But what about fish?

Are they able to pass on information, such as the location of food supplies, warnings of imminent danger and the desire to mate? With the transmission of such information being so important for survival, it is hard to imagine that they cannot react to one another in some form or other.

WARNING SIGNS

Perhaps one of the most common forms of communication is body language and this is something that we see in many fish species.

If you have ever watched a shoal of roach or minnows moving almost as one as they turn in unison, then you will be well aware that fish do exhibit body language and react to each other. For this to occur, and for shoals to form at all, must mean that fish recognise other individuals of the same species. It is thought that this ‘imprinting’ takes place soon after hatching, with fish associating with those that hatch around them.

Body language in shoaling fish can also indicate the presence of danger, such as the approach of a predator. With an arched body and fins held erect, fish can signal danger very effectively. It only takes one individual to alert a huge shoal of fish to a threat, because the signal quickly passes from fish to fish.

This same form of body language could signal the presence of a rig or bait that some have been caught on before to others seeing it for the first time. It is unlikely that the naive fish know what is putting their shoal-mates on edge, but they are sure to react to it by being guarded.

Chub are a species known for being crafty and, in a bid to stop the fish relaying warning signals to any shoal mates in the vicinity, many specimen anglers go out of their way to retain any fish caught in a keepnet, or put them back well upstream of where they have just been caught (as most chub bolt upstream once returned).

SHOW OF STRENGTH

Most coarse fish do not have complex mating rituals or show off to their potential mates or ward off rivals. Other fish are much more showy. African cichlids use body language to perform complex mating rituals and to discourage competing males. The same fish also build large pits from which to display during their spawning courtship, the size of the excavation being linked to the size and fitness of the male.

Many species of animal, including fish, use displays to signal their strength to rivals. Even bream are thought to hold a territory and defend it from other males, primarily with a show of strength.

These non-conflict behaviours make a lot of sense, especially among species which have more serious armaments. Large sharks, for example, may swim parallel to other individuals in a show of strength that keeps them at a distance from their competitors’ razor-sharp teeth. They roll their eyes and arch their bodies to indicate their size and willingness to attack.

SOUND AND VISION

Some fish species are able to communicate by sending out sound waves. Fish have quite complex hearing organs buried in their heads that can pick up sound waves, in the form of vibrations, travelling through the water. Cod are able to communicate with their shoal-mates by producing a sound through their swim bladders. This low-pitched drumming can travel several hundred metres, alerting other fish of their presence.

Other fish species may make sounds as they crunch up tough foods, such as mollusc shells. This could alert and attract other individuals to potentially rich feeding grounds.

Rolling and especially jumping, often seen in carp and several other coarse species, could also be partially a response to finding good feeding areas and wanting to signal this discovery to other fish. The sound will certainly travel a good distance in water, much further than in air, so this remains one of several possible reasons for this behaviour.

Pheromones, chemicals produced by animals and plants specifically for the purpose of communication, are widely known and for many years were investigated in fish. While there still remains some evidence that fish can respond to certain chemicals in the water, especially around spawning time, much of the evidence suggesting that fish release pheromones when attacked or damaged by predators has now been debunked.

Although they don’t have the same communication strategies seen in other types of fish, exactly how coarse fish signal to each other remains a fascinating subject.