Interspecific Variation of Photoreceptors in Four Co-Existing Haplochromine Cichlid Fishes

Abstract

The photoreceptors of four co-existing haplochromine cichlids have been studied morphometrically and microspectrophotometrically, and the results were interpreted in terms of resolution and sensitivity. Among the three species, Haplochromis argens, H. piceatus and H. ishmaeli, the cone dimensions and the visual pigments differed only slightly, in spite of differences in vertical distribution and feeding behaviour between these species. The fourth species H. pyrrhocephalus showed distinctly different visual properties, with very large double cones at low densities, and its spectral sensitivity shifted to significantly longer wavelengths. To some degree, the photoreceptor morphometries and visual pigments appeared to be attuned to the photic conditions of the specific habitats. The two species H. piceatus and H. pyrrhocephalus, occupying a dimmer habitat with less penetrating blue light, had reduced blue sensitive single cones, whereas the surface dwelling species H. argens had relatively small red/green sensitive double cones. Also an attempt has been made to relate the visual capacity of the cichlids to their behavioural patterns, focussing on prey detection. The greatest visual differences were observed in the two species H. argens and H. pyrrhocephalus, with resource coincidence and with the highest encounter frequency, which may indicate that visual segregation contributes towards reducing interference competition among co-existing species with a similar diet.

Retinal specialization through spatially varying cell densities and opsin coexpression in cichlid fish

“…The area centralis has higher visual acuity and is likely important for looking forward for object recognition and discrimination. The estimated SRP of 4.5 cycles deg −1 in a Lake Malawi cichlid is similar to values obtained from Lake Victorian cichlids (SRP=3.3 to 3.9 cycles deg −1 ; van der Meer and Bowmaker, 1995 Collin and Pettigrew, 1989]. Although cichlids do not appear to have particularly high spatial resolution, our calculations indicate that the visual acuity of M. zebra is sufficient for key tasks involved in recognizing colour pattern elements for communication and discriminating prey items in foraging.…”

Cichlid fish visual systems: mechanisms of spectral tuning

“…Here, we focus on cones as they are the photoreceptors operating under bright light conditions important for foraging and mating. Studies using microspectrophotometry (MSP) have shown that fish can express as many as four distinct cone visual pigments, each one tuned to a different portion of the spectrum (Loew & Lythgoe 1978;Bowmaker 1995).…”

“…Fish cones have either a single or a double cone morphology (Walls 1942;Bowmaker 1995). Single cones tend to be smaller and contain shorter wavelength sensitive visual pigments.…”

Electrophysiological assessment of spectral sensitivity in adult Nile tilapia Oreochromis niloticus: evidence for violet sensitivity

“…Spectral sensitivity curves in cichlids, recorded using electroretinograms (ERGs), are modelled more adequately with four visual pigments as opposed to three (Garner et al, 2003). Unfortunately there have been few attempts to assess spectral sensitivity using electrophysiological or psychophysical techniques in cichlids (Bell, 1982;Allen and Fernald, 1985;Garner et al, 2003) and so our current predictions about the wavelength discrimination capabilities of cichlids are largely limited to MSP measurements of visual pigments in situ or in a reconstituted form (van der Meer and Bowmaker, 1995;Carleton et al, 2000;Parry et al, 2005;Jordan et al, 2006;Spady et al, 2006;Carleton et al, 2008). MSP is a powerful technique but, as indicated above, it is possible to overlook cells containing a particular visual pigment because of an inadequate number of sample scans, or because of the regionalization of a class of pigments within the retina, they may not be present in the area of retina examined (Bowmaker et al, 1991;Shand, 1993).…”