New Zealand Journal of Marine and Freshwater Research abstracts
Changes in visual morphology through life history stages
of the New Zealand snapper, Pagrus auratus
P. M. PANKHURST1
R. EAGAR
School of Biological Sciences
University of Auckland
Private Bag 92019
Auckland, New Zealand
1Present address: Department of Aquaculture, University of Tasmania
at Launceston, P. O. Box 1214, Launceston, Tasmania 7250, Australia
Abstract Plastic resin histology and transmission electron
microscopy were used to examine the development of the retina in snapper
Pagrus auratus (Bloch & Schneider, 1801) larvae before, and
at the onset of feeding. Light microscopy was used to examine changes in ocular
morphology with increasing body size, in larval, juvenile, and adult P.
auratus. There was a 96-fold increase in eye size, from 0.23 mm diameter in
a 4-day-old larva (3.42 mm standard length), to a maximum of 22 mm diameter in
an adult of 333 mm fork length. Cells of the presumptive optic cup were
undifferentiated in fish larvae at the time of hatching. Development of the eye
proceeded rapidly so that at 3 days of age, a pigmented cone retina had formed
and the optic nerve connected to the optic tectum. On the fourth day after
hatching, the lens had become crystalline, and synaptic ribbons and vesicles
were present in the cone cell synaptic junctions, indicating that the retina
was now functional. This coincided with the onset of feeding behaviour in the
fish larvae. Putative rod precursor cells were present in fish at 18 days of
age. Juvenile and adult fish had duplex retinae with cones arranged in a
regular mosaic in which four equal double cones surrounded a central single
cone. Cone ellipsoid diameter increased during eye enlargement to maintain a
closely packed array in fish of all sizes. Angular density of cones continued
to increase with increasing eye size such that theoretical spatial acuity
increased from 2deg.1' (Minimum Separable Angle, MSA) in a 4-day-old fish, to
asymptotic values of between 3' and 4' (MSA) in adult fish.
Keywords vision; morphology; acuity; sparidae;
photoreceptor
New Zealand Journal of Marine and Freshwater Research, 1996: Vol. 30:
79-90
0028-8330/96/3001-0079 $2.50/0 (c) The Royal Society of New Zealand
1996
PDF file of entire paper: medium quality (2281K); (scanned from paper original: notes about this process)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
