Visual Resolution during Growth in a Cichlid Fish: A Morphological and Behavioural Case Study

Abstract

The spatial resolution of the visual system during growth of the cichlid fish Haplochromis argens was deduced from the cone density according to two models of possible connectivity patterns. The models include a convergency type of 5 cones per visual unit and a divergency type of 1.25 cones per visual unit. The minimum separable angle in this species was measured during ontogeny using operant conditioning in a two choice discrete trial situation. As a consequence of the moderate performances of the juveniles, the behavioural study showed a greater change of visual resolution than was predicted by the morphology. The minimum separable angle of the adult fishes was accurately predicted by the 'divergency model', which led to rejection of the other morphological model. It is argued that the high resolution as found in some other fish species by authors using the same technique may be due to imperfect calculations.

Vision in the grass goby,Zosterisessor ophiocephalus(Teleostei, Gobiidae): A morphological and behavioural study

“…In Z. ophiocephalus, the calculated histological visual acuity was better than the behavioural one, as reported in other fish species (review in Douglas & Hawryshyn, 1990;Browman et al, 1990;van der Meer, 1995;Wanzenbock et al, 1996). Estimates of visual acuity based upon inter-cone spacing could be higher than those observed behaviourally because counts of cell density alone do not take signal convergence and processing into account (Browman et al, 1990).…”

Proximate and ultimate causes of variable visual sensitivities: Insights from cichlid fish radiations

“…This was supported by A1:A2 chromophore ratio measurements of 10:1 by high pressure liquid chromatography (Sugawara et al 2005). However, Lake Victorian cichlids have been found to use A1 or A1/A2 mixtures (van der Meer 1995, Terai et al 2006, Miyagi et al 2012). MSP measurements of the long wavelength sensitive pigments had λ max of 595 nm or longer in some Victorian species.…”

“…Fish eyes then continue to grow throughout life with new cone photoreceptors being added at the retinal margin (Fernald 1990). The cone mosaic seems to be stable throughout life with no sign of cell death or cell loss through development (Hagedorn and Fernald 1992, van der Meer 1995, Braekevelt et al 1998). Therefore, the majority of any changes in opsin gene expression in adults must result within existing photoreceptors as the proteins of their outer segments turnover, rather than from the gain or loss of additional cells.…”

Vision in the southern hemisphere lampreyMordacia mordax: Spatial distribution, spectral absorption characteristics, and optical sensitivity of a single class of retinal photoreceptor

“…The estimate of spatial resolving power (1.7 cycles0deg) and minimum separable angle (34 ' 7 '' ), based on photoreceptor spacing, is lower than in teleosts such as the white crappie Pomoxis annularis (7 ' 0 '' , Browman et al, 1990), the convict fish Microcanthus strigatus (3 ' 36 '' , Yamanouchi, 1956;Nakamura, 1968), the bluegill sunfish Lepomis macrochirus (2 ' 42 '' , Williamson & Keast, 1988), the cichlid Haplochromis argens (11 ' , van der Meer, 1995), and a range of marine species examined by Tamura (1957) who found acuities from 4 ' 12 '' to 15 ' 24 '' . Considering that there is often an appreciable convergence of information onto the output or ganglion cells and that behavioral acuity is constrained by their spacing (Collin & Pettigrew, 1989), the spatial resolution of M. mordax may be even less.…”