Evelyn Shaw

Methods for measuring the three-dimensional structure of fish schools

Abstract Two methods are described for measuring the three-dimensional co-ordinates of the individual fish in a school photographed from above. The Stereo Method uses a double-prism device which produces two images on the film taken from positions slightly apart, and the distance of the fish from the camera can be determined by its parallax against the background. The Shadow Method depends on the fact that the shadow of a an object in the sun is farther to the side the higher the object above the background. The coordinates in the horizontal plane are easily determined once the distance of the fish from the background is known. The advantages and disadvantages of the two methods are considered, and a sample set of photographs of a school of 10 pilchards, made with the Shadow Method, is analysed. These results are then used to calculate the distance and bearing in the horizontal and vertical planes between nearest neighbours in the school, and to give information about the regularities in geometrical spacing of the fish. The photographs were also measured to show to what extent the fish were swimming parallel.

The optomotor reaction of schooling carangid fishes

Abstract Carangid fishes were tested in an optomotor apparatus and their orientation to different kinds of stimuli was observed. The fish did not orient to any particular region of the stimulus consisting of uniform black and white vertical stripes. The r.p.m. of the fish was generally greater than the r.p.m. of the drum. On the other hand, the fish oriented to the panel stimulus and tended to remain near it during the entire range of revolutions. The r.p.m. of the fish closely followed the r.p.m. of the drum. Certain features of the behaviour of the fish in an optomotor apparatus are compared with certain features of schooling under natural conditions.

Refractive Error and Vision in Fishes

The eyes of living immersed herring and silversides are farsighted and require greater hypermetropic correction for lateral vision than for anterior vision. Comparisons of lens-to-retina distances in frozen material with focal lengths of lenses are consistent with the degree of hypermetropy found by retinoscopy.