A COMPARATIVE STUDY OF RETINAL STRUCTURE IN SOME FISHES FROM MODERATELY DEEP WATERS OF THE WESTERN NORTH ATLANTIC

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Abstract
Examination of the retinae of 13 species from waters off Labrador shows that the retinal layers are closely related with one another in their development and that the general retinal features vary with habitat depth. The retinae of Aspidophoroides monopterygius, Triglops ommatistius, and Gadus callarias with as yet well-developed pigment epithelium, many cones, and conducting elements appear to be capable of functioning fairly normally even in a brighter environment. The retinae of Lycodes lavalaei, L. vahlii maculatus, Sebastes marinus marinus, and S. m. mentella with degenerating pigment epithelium, numerous rods, and poor conducting elements are presumably not any longer suitable for bright light vision. The pure rod retinae of Notoscopelus kröyeri, Ceratoscopelus maderensis, and Argentina situs are different from those of Macrourus bairdii, Coryphaenoides rupestris, and Antimora rostrata in having much better developed layers of conducting elements. This may mean that, in the former three species, form perception plays a significant role, while it is of little importance in the latter three species which are adapted completely to a habitat with only very meager light. In the cone-bearing species, with the exception of A. monopterygius and G. callarias, the cones are mostly of the twin type. This contradicts the generally held opinion that twin cones seem to be associated with vision in bright light.