charleyvtl.nl

vision-in-cichlids.com

Vision in Cichlids :: by Dr. H.J. van der Meer

http://www.vision-in-cichlids.com/optomotor_response.htm

The ontogenetic alteration of photopic and scotopic sensitivity thresholds were measured using optomotor response in. Haplochroms sauvagei, H. argens. The fishes were exposed to a horizontally moving pattern of vertical lines, which enforced them to swim along as long as the lines were visible (after Van der Meer, 1991. Van der Meer, 1994. The major aim of this investigation was to test the predicted morphological data on sensitivity (photopic and scotopic thresholds) during growth in these species.

vision-in-cichlids.com

Vision in Cichlids :: by Dr. H.J. van der Meer

http://www.vision-in-cichlids.com/cv.htm

Dr H J. (Henny) van der Meer (1946). 2513 GG Den Haag. 7, Grande Rue. Laan van Meerdervoort 57. 2517 AG Den Haag. After secondary school (Rijswijks Lyceum) I attended the Nederlandse Fotovakschool, meanwhile playing guitar in several rock ‘n roll gigs. Subsequently I fulfilled various jobs in the photo-industry and from 1969 till 1971 I worked as a photographer on the ss Statendam of the Holland America Line, which provided me an opportunity to travel around the world. In the 1990s I began teaching biolo...

vision-in-cichlids.com

Vision in Cichlids :: by Dr. H.J. van der Meer

http://www.vision-in-cichlids.com/recovery_general.htm

During the past decades, dramatic changes were observed in the ecosystem of Lake Victoria (cited from Witte et al., 2005. The introduced Nile perch (. And the introduced Nile tilapia (. In the 1990s, after a decline of the Nile perch due to over-fishing, some 20 haplochromine species were recovered in the Mwanza Gulf. With respect to their trophic preference, 80% of these recovered haplochromines were zooplanktivores (three species) and about 15 % were detritivores (four species; Witte, et al., 2...Apart...

vision-in-cichlids.com

Vision in Cichlids :: by Dr. H.J. van der Meer

http://www.vision-in-cichlids.com/introduction.htm

Behavioural measurements enable to establish visual abilities of the system as a whole. The measurements should be concentrated on a specific ability, like acuity, colour discrimination, threshold value, polarization sensitivity, etc. One can also measure natural behaviour that is visually generated, like food detection and gender recognition but one must be sure that no other sense organs are involved. A review on behavioural studies of fish vision is found in Douglas and Hawryshyn (1990). In haplochrom...

vision-in-cichlids.com

Vision in Cichlids :: by Dr. H.J. van der Meer

http://www.vision-in-cichlids.com/operant_conditioning.htm

The visual acuity of. Was measured during ontogeny using operant conditioning in a two choice discrete trial situation (cited from Van der Meer, 1995. The fishes were trained to distinguish a chess-board pattern from a grey target with the same overall luminance. The size of the squares were diminished until the fish was no longer able to distinguish the two targets. The major aim of the investigation was to test the predicted morphological data on resolution during growth in this species. The dispenser ...

vision-in-cichlids.com

Vision in Cichlids :: by Dr. H.J. van der Meer

http://www.vision-in-cichlids.com/colour_vision.htm

Colour vision can be defined as the ability of an organism to distinguish and recognize spectral compositions of light through its visual system. The definition includes at least two necessary conditions of this system: the simultaneous use of at least two different types of photoreceptors and the appropriate neuronal pathway to facilitate this spectral perception. Parry et al., 2005. Verweij et al., 1996. From a philosophical point of view, Thompson (1995). Argued that the biological function of colour ...

vision-in-cichlids.com

Vision in Cichlids :: by Dr. H.J. van der Meer

http://www.vision-in-cichlids.com/fenotypic_plasticity.htm

The retinal form variations among haplochromine cichlids could be the result of phenotypic plasticity: environmentally induced acceleration or retardation of development of individual parts relative to other parts without alteration of the genetic program of development ( Smith-Gill, 1983. The phenotype can vary within the limits set by the genetically determined ‘norm of reaction’, which could be a significant mechanism in the evolutionary development ( Schlichting, 1986. Zeutzius et al., 1984. The reti...

vision-in-cichlids.com

Vision in Cichlids :: by Dr. H.J. van der Meer

http://www.vision-in-cichlids.com/lake_victoria.htm

Lake Victoria and its fish fauna. Lake Victoria is the world’s largest tropical lake by area (cited from Witte et al., 2005. Bound by Tanzania, Uganda and Kenya, it straddles the equator in eastern Africa. Lake Victoria has a surface area of ca. 68,800 km2, a maximum depth of about 70 m and is situated at an altitude of 1134 m above sea level. The lake originated less than a million years ago and probably even dried up completely ca. 14,000 years ago ( Johnson et al., 1996. Witte and Van Oijen, 1995.

vision-in-cichlids.com

Vision in Cichlids :: by Dr. H.J. van der Meer

http://www.vision-in-cichlids.com/cichlid_eye.htm

The cichlid eye does not specifically differ from the general fisheye. Two slightly forward directed, laterally placed bowl-shaped structures with spherical lenses that cannot be distorted. The crystalline lenses are layered, somewhat like onions, with an increasing refraction index from the periphery towards the centre, which considerably lessens the spherical and chromatic aberration of the eye lens ( Jagger, 1992. Points out that the fixed focal length (. Varies inter-specifically between 1.99. Kröger...