INTERSPECIFIC ALLOMETRY OF THE TELEOST VISUAL-SYSTEM - A NEW APPROACH

The capabilities of spatial vision of 31 species of fishes were estima ted using a mathematical model that is based upon the allometry of the eye and the retinorecipient tectal layers, the Stratum opticum (SO) a nd the Stratum fibrosum et griseum superficiale (SFGS). The four param eters 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 pr ojection within these layers. The visual index is defined as the produ ct of these parameters, which show a high mutual positive correlation. The volume of SO + SFGS is, irrespective of fish size and species, li nearly proportional to the retinal surface area. To establish intraspe cific allometric relations, the allometric function y = kx(d)(1-alogx) was used, With d being a natural number dependent on the dimensions o f x and y. The visual index correlates with published data on psychoph ysically determined minimum resolvable angles and it appears to be int errelated with behavioural and environmental characteristics. High ind ices are characteristic of pelagic, diurnal species living in clear wa ters and are mostly found among predatory and especially piscivorous s pecies. Species with low indices live in turbid waters and/or are ofte n benthic. Water depth and social behaviour appear to be unrelated to the visual index. The visibility is the characteristic which is strong est related to the visual index.