AQUATIC SCHOOLS
Many species of fish, particularly smaller fish, travel in schools, moving in tight formations often with the precision of the most highly disciplined military unit on parade. (1) Some move in synchronized hordes, while others move in starkly geometric forms. (2) In addition to the varieties of shapes of schools of fish, there are countless varieties of schooling behaviors. (3) Some fish coalesce into schools and then spread out in random patterns, while others move into close formations at specific times, such as feeding times, but are more spread out at other times. (4) Some move in schools composed of members of all age groups, while others move in schools predominantly when they are young but take up a more solitary existence as they mature. Though this behavior is quite a regular, familiar phenomenon, there is much that is not completely known about it, particularly the exact function that it serves and what mechanisms fish use to make it happen.
Numerous hypotheses have been proposed and tested concerning the purpose of schooling behavior in fish. Schooling certainly promotes the survival of the species, but questions arise as to the way the schooling enables fish to have a better chance of surviving. Certainly, the fact that fish congregate together in schools helps to ensure their survival in that schooling provides numerous types of protection for the members of the school. One form of protection derives from the sheer numbers in the school. When a predator attacks a school containing a huge number of fish, the predator will be able to consume only a small percentage of the school. Whereas some of the members of the school will be lost to the predator, the majority of the school will be able to survive. Another form of protection comes from the special coloration and markings of different types of fish. Certain types of coloration or markings such as stripes or patterns in vibrant and shiny colors create a visual effect when huge numbers of the fish are clustered together, making it more difficult for a potential predator to focus on specific members of the school. A final form of protection comes from a special sense that fish possess, a sense that is enhanced when fish swim in schools. This special sense is related to a set of lateral line organs that consist of rows of pores leading to fluid-filled canals. These organs are sensitive to minute vibrations in the water. The thousands of sets of those special organs in a school of fish together can prove very effective in warning the school about an approaching threat.
(1) It is also unclear exactly how fish manage to maintain their tight formations. (2) Sight seems to play a role in the ability of fish to move in schools, and some scientists believe that, at least in some species, sight may play the principal role. (3) However, many experiments indicate that more than sight is involved. Some fish school quite well in the dark or in murky water where visibility is extremely limited. (4) This indicates that senses other than eyesight must be involved in enabling the schooling behavior. The lateral line system most likely plays a significant role in the ability of fish to school. Because these lateral line organs are sensitive to the most minute vibrations and currents, this organ system may be used by fish to detect movements among members of their school even when eyesight is limited or unavailable.