We have initiated a genetic analysis of the zebrafish visual system to
identify novel molecules involved in vertebrate retinal function. Zeb
rafish are highly visual; they have four types of cones as well as rod
photoreceptors, making it possible to study both rod and cone-mediate
d visual responses. To identify visual mutants, optokinetic responses
of mutagenized larvae are measured in a three-generation screen for re
cessive mutations. By measuring visual behavior our genetic screen has
been targeted towards identifying mutants that do not have gross morp
hological abnormalities. The electroretinogram (ERG) of optokinetic-de
fective mutants is recorded and their retinas are examined histologica
lly to localize defects to the retina. In this report, we summarize ou
r screening results and ERG and histological analyses of the five morp
hologically normal mutants we have analyzed to date. Additionally, the
more detailed characterization of a red-blind mutant that we have iso
lated is summarized. Our results indicate that mutants with defects in
various processes such as photoreceptor synaptic transmission, photor
eceptor adaptation and cell-type specific survival and/or function can
be identified using this approach. (C) 1998 Published by Elsevier Sci
ence Ltd. All rights reserved.