Constructional morphology of photoreceptor patterns in percomorph fish

The frequently occurring photoreceptor patterns in fish are explained using functional and environmental demands in a geometric model. The shape of the double cone provides a number of constructional properties leading to a limited number of appropriate configurations. The probability of their occurrence is estimated from the degree to which the combination of properties of each configuration meets specific environmental light conditions. A row pattern of merely double cones is especially suitable for vision in a dim homochromatic environment; a triangular pattern is quite appropriate for high resolution and accurate movement detection, whereas the known square pattern has a high adaptive capacity to varying spectral distributions. In this context the transforming capacities of both square and row patterns can be understood.Frequently used abbreviations Ad area of double elements per pattern unit - ARC area ratio of cone types - As area of single elements per pattern unit - DHR degree of homogeneous resolution - dZ range of variation of Z - HDC homogeneous distribution of cone types - NRC number ratio of cone types - O area of pattern unit - Q ratio between dZ and VAR - R radius of single element - r radius of one intersecting circle of double element - Sd area of one double element - Ss area of one single element - SYM order of symmetry - VAR variation of the ARC - Z packing