PERIODIC CONE CELL TWISTS IN THE WALLEYE, STIZOSTEDION-VITREUM - A NEW-TYPE OF RETINOMOTOR ACTIVITY

Atypical retinomotor movements (RM) have been found in a localized are a of the retina of the walleye, Stizostedion vitreum. The ellipsoid an d outer segment of regions of twin cones in an oblong region of the ce ntral retina rotate, twisting about their axes at intervals throughout the 24 hr day. This twist results in a local, cyclic change of the co ne mosaic, from the predominant row type to a square type. The cone ce ll myoids extend slightly, but the cone ellipsoids remain relatively c lose to the outer limiting membrane (OLM). Throughout the retina, rod cells exhibit ubiquitous extension and contraction of their myoid regi ons coincident with changes in illumination as is typical of fishes wi th duplex retinas. These retinomotor movements first appear around 6 w eeks of age, and persist throughout growth, becoming more pronounced w ith maturity. Stizostedion vitreum is the first fish observed with thi s type of cone RM activity.