THE VISUAL FIELD IN THE WINTER FLOUNDER(PseudopleuronectES
americanus) THROUGH STAGES OF METAMORPHOSIS.

LISA SCANLON
SCHOOL OF SCIENCE AND NATURAL RESOURCES
LAKE SUPERIOR STATE UNIVERSITY
SAULT STE. MARIE, MICHIGAN 49783
NOVEMBER 5, 1996

Astract:	At approximately 2 months after hatching the winter flounder
( Pseudopleuronectes arnericanus) undergoes a metamorphic change. A pre-metamorphic
flounder has an eye on each side of the head. As it reaches appfoximately day 65 the left
migrates across the head to join the right eye. By approximately day 70, after
metamorphosis, both eyes are now on top of the head allowing an overlap in the visual
field. The winter flounder swims with his blind side down parallel to the ocean floor
where it spends the remainder of its life. I questioned whether the winter flounder's visual
field could be mapped by using fixed eyes embedded in plastic and whether or not this
represents reality. For my study I used a developmental series of winter flounder from
hatching through metamorphosis. These samples had been previously embedded in
plastic, sectioned at 3 microns and affixed to microscope slides. Using a video camera
connected to the microscope, measurements of the lens diameter, the distance from the
center ofthe lens to the photoreceptor layer, center ofthe lens to the midpoint between
the eyes and maximum angles of light entry were taken from the television screen. These
measurements were used to determine the angle of the visual field and the distance from
the eye where prey objects would be in focus. Results for early developmental stages were
realistic, however post-metamorphic samples yielded negative focal points, which means
they were focusing inside the lens. An interpretation of Pre-metamorphic flounders are so
tiny that the focal point can be determined accurately by fixed eyes embedded in plastic.
However, after metamorphosis the eye is large, such that during the fixation process the
eye collapsed and the focal point does not represent reality. A possible solution would be
creating a new technique for fixation and embedding of the eyes in plastic such that
shrinkage does not occur.
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