Vision in elasmobranchs:histology of the retina and erg spectral sensitivity

This thesis is concerned with the retinal histology and scotopic (dark adapted) spectral sensitivity of three species of elasmobranch as determined by electroretinography. The cellular makeup of the retinas of each species of elasmobranch will be discussed as well as a determination of rod to bipolar cell and rod to ganglion cell ratios. The purpose will be to determine whether the retinal histology and spectral response appears adaptive to the species' habitat. The three species studied are the sixgill shark, Hexanchus griseus (Bonnaterre), the leopard shark, Triakis semifasciata Girard, and the shove I nose guitarfish, Rhinobatos productus (Ayres). Hexanchus griseus is a primitive deep sea shark found in depths ranging from 75 fathoms to as deep as 3430 fathoms (Bigelow and Schroeder, 1948). I have caught specimens in depths ranging from 70 to 150 fathoms. Triakis semifasciata is found in rather shallow waters and in sloughs (Roedel, 1950). Rhinobatos productus inhabits the shallow waters of shores and bays (Barnhart, 1936).