The shoals are often more than 7 km long, 1.5 km wide and 30 metres deep and are clearly visible from spotter planes or from the surface. Sardines group together when they are threatened. This instinctual behaviour is a defence mechanism, as lone individuals are more likely to be eaten than large groups.
The shoaling habit includes all the popular, common fish that belong to the Characin family (tetras), Cyprinidae family (barbs and danios) and Melanotaeniidae family (rainbow fish). There are even some species of catfish and cichlids that shoal.
- Why do fish swim in shoals?
Many kinds of fish prefer to swim together in groups called shoals. ... Shoaling can help fish because there are more eyes for spotting danger from predators or for finding food. Predators also find it more difficult to target a single victim in a big, moving group.