Interspecific Allometry of the Teleost Visual System; a New Approach

The capabilities of spatial vision of 31 species of fishes were estimated using a mathematical model that is based upon the allometry of the eye and the retinorecipient tectal layers, the Stratum opticum (SO) and the Stratum fibrosum et griseum superficiale (SFGS). The four parameters of the model are the focal length of the eye, the linear size of SO + SFGS, the thickness of SO + SFGS and the density of the optic projection within these layers. The visual index is defined as the product of these parameters, which show a high mutual positive correlation. The volume of SO + SFGS is, irrespective of fish size and species, linearly proportional to the retinal surface area. To establish intraspecific allometric relations, the allometric function y = kxd(1-alogx) was used, with d being a natural number dependent on the dimensions of x and y. The visual index correlates with published data on psychophysically determined minimum resolvable angles and it appears to be interrelated with behavioural and environmental characteristics. High indices are characteristic of pelagic, diurnal species living in clear waters and are mostly found among predatory and especially piscivorous species. Species with low indices live in turbid waters and/or are often benthic. Water depth and social behaviour appear to be unrelated to the visual index. The visibility is the characteristic which is strongest related to the visual index.