ABSTRACT
Shoaling behaviour is extremely common amongst teleost fishes. Of the 27,000 species, approximately 50% live in shoals as juveniles and 25% maintain the behavioural trait throughout their lives (Shaw, 1978). The decision to join a shoal represents the outcome of a cost benefit trade-off, which may be influenced by a number of factors including predation risk, parasite load, body size, nutritional state, the availability and distribution of resources, and reproductive strategies (Krause and Ruxton, 2002). As a result, there is great variability in the degree of shoaling tendency both
within and between species. For example, some species (particularly pelagic oceanic species) form polarized groups (schools) which may consist of many thousands of individuals, whilst other species form more dynamic non-polarized groups (shoals) which often comprise only a few individuals, particularly in freshwater species.
