Publication: Retinal and lenticular ultrastructure in the
aestivating salamanderfish, Lepidogalaxias
salamandroides (Galaxiidae, Teleostei) with special
reference to a new type of photoreceptor mosaic
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Date
1998
Authors
Collin, S.P. ; Collin, H.B.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
The salamanderfish, Lepidogalaxias
salamarzdroides (Galaxiidae, Teleostei) is endemic to
southwestern Australia and inhabits shallow, freshwater
pools which evaporate during the hot summer months.
Burrowing into the substrate in response to falling water
levels allows these fish to aestivate for extended periods
of time while encapsulated in a mucous cocoon even
when the pools contain no water. Only a few minutes
after a major rainfall, these fish emerge into relatively
clear water which subsequently becomes laden with
tannin, turning the water black and reducing the pH to
approximately 4.3. As part of a large study of the visual
adaptations of this unique species, the retinal and
lenticular morphology of the aestivating salamanderfish
is examined at the level of the light and electron
microscopes. The inner retina is highly vascularised by a
complex system of vitreal blood vessels, while the outer
retina receives a blood supply by diffusion from a
choriocapillaris. This increased retinal blood supply may
be an adaptation for reducing the oxygen tension during
critical periods of aestivation. Large numbers of Miiller
cells traverse the thickness of the retina from the inner to
the outer limiting membranes. The ganglion cells are
arranged in two ill-defined layers, separated from a thick
inner nuclear layer containing two layers of horizontal
cells by a soma-free inner plexiform layer. The photoreceptors
can be divided into three types typical of many
early actinopterygian representatives; equal double
cones, small single cones and large rods (2:1:1). These
photoreceptors are arranged into a unique regular square
mosaic comprising a large rod bordered by four equal
double cones with a small single cone located at the
corner of each repeating unit. The double cones may
optimise perception of mobile prey which it tracks by
flexion of its head and "neck" and the large rods may
Offprint requests to: Dr. Shaun P. Collin, Marine Neurobiology
Laboratory. Department of Zoology, University of Western Australia,
Nedlands 6907, Western Australia, Australia. Fax: (08) 9380 1029.
ernail: scollin@cyllene.uwa.edu.au
increase sensitivity in the dark tannin-rich waters in
which it lives. Each single cone also possesses a dense
collection of polysomes and glycogen (a paraboloid)
beneath its ellipsoid, the first such finding in teleosts.
The retinal pigment epithelium possesses melanosomes,
phagocytes and a large number of mitochondria. The
anatomy of the retina and the photoreceptor mosaic is
discussed in relation to the primitive phylogeny of this
species and its unique life history.
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