Just for the love of water, I decided to try shallow water diving at the beach in Mombasa. I wanted to get the feeling of being completely immersed in water. The breathing tube I had on restricted me from going deep enough to get away from the noise above the water level. So I never really got to experience what happens deep inside the ocean. Teaming with different species of animals in the ocean world, is there noise under water? I asked this question to one of my friends who was a marine photographer earlier in his career. He had a ready answer for me.
Animals can communicate with one another in whatever medium they inhabit. Some of their voices can be heard by the human ear, some can only be recorded by very sensitive machines. Just as frogs and toads converse obviously and vocally across a pond or lake, the fish beneath the surface can also communicate freely. Indeed, as my marine biologist said, water is a better medium for transmission than commonly realised, at least so far as acoustic signals are concerned. Optically, water offers a poor channel, diffusing and distorting visual information through refraction and bending of light. But sound travels extremely well in water. Several hundred species of fish that emit sound will testify to that.
Fish give out a wide range of calls in several ways. Some rub their teeth or spines together, some change speed and direction in order to affect the flow of water, and some use their swim bladder as a resonating chamber controlled by muscle action. They appear to emit their calls on the move, suggesting perhaps that sound may be important in helping maintain the cohesion of a school, which can sometimes comprise a few million individuals. But sometimes grouping has its drawbacks. The swimming sounds made by a large school of fish will give away their presence to the marauding predators and also make them unable to detect oncoming threats.
We, too, could probably profit from knowing more about the language of fish. After all, fishermen are in the business of locating edible wildlife, so there could be some economic advantage in an ability to eavesdrop on our aquatic relatives. A researcher, Dr Antony Hawkins, using hydrophones submerged in water, has actually recorded various sonic sounds in the form of knocks and grunts from fish. This has been recorded during shows of male aggression, defensive or escape sounds. The most interesting part is what happens during mating and spawning. By breeding fish in a large tank for observation purposes, scientists have been able to record a characteristic sequence of courtship sounds. The male begins with aggressive knocking calls thereby establishing his sexual sway over a chosen female. As he swims around her, the knocking sounds gradually speed up and the frequency becomes higher until they reach the level of an excited purring, like that of a domestic cat. This seems to have a marked triggering effect on the physiological responses of the female who begins to spawn her eggs, 10,000 or so of them, all the while remaining curiously silent as she floats to the surface locked in a quiet embrace with her partner.
The calls and sounds made by other economically useful fish such as the salmon have been investigated and documented. This brings the prospect of our acquiring a full range of the vocabulary of fish courtship. This could be valuable in controlling the mating and spawning activities of some fish species that have long escaped the attention of fishermen. We may even learn to direct the mating of fish to our own ends, manipulating them through the language they understand best – their own language. Much has been done to take advantage of using fish ponds for commercial purposes. All this has been done mainly from the knowledge of the nutritional needs and behaviours of fish. But we miss out what might have been if the fish had not only been bred within their own habitat, but also within the reach and total control of fishermen who speak to them in their own language. It can be done.