The Attitude of Fish Eye-Lines in Relation to Body Shape and to Stripes and Bars

An understanding of the adaptive significance of the attitude of the eyeline is aided by a consideration of the behavior and habitat of the fish in relation to the general color pattern.

Abstract

The function of obliterative eye-lines has gained general acceptance, but no one has attempted to account for the variability shown in the inclination of the line. There is a clear relationship between the steepness of the line and (a) the body shape of the species, and also with (b) the angle of the forehead. Vertical eye-lines are associated with deep bodies and steep foreheads, while horizontal lines are characteristic of the more elongate species with low foreheads; exceptions prove of considerable interest. An understanding of the adaptive significance of the attitude of the eyeline is aided by a consideration of the behavior and habitat of the fish in relation to the general color pattern. Longitudinal stripes occur on slender species that swim fast, whereas vertical bars typify deep-bodied fishes that turn sharply. The more closely a striped slender species is associated with the bottom, the more stripes it is apt to have. Barred species usually have deep bodies and live close to the substrate. Stripes or bars simultaneously serve as social signals and as antipredator markings.