title: Topographic analysis of the ganglion cell layer in the retina of the four-eyed fish Anableps anableps.
abstract: Fish of the genus Anableps (Anablepidae, Cyprinodontiformes) have eyes that are adapted for simultaneous aerial and aquatic vision. In this study we investigate some of the corresponding retinal specializations of the adult Anableps anableps eye using retinal transverse sections and wholemounts. The linear dimensions of the retina were found to be asymmetric with a greater representation of the dorsal compared to the ventral visual field. The total number of neurons in the ganglion cell layer of the ventral hemiretina was on average 3.6 times greater than the values obtained in the dorsal hemiretina. Isodensity contour maps revealed a prominent horizontal visual streak in the ventral hemiretina with an average peak cell density of 18,286 cells/mm(2). A second less-well-developed horizontal visual streak was also observed in the dorsal hemiretina. A sub-population of large cells with soma areas between 74 and 188 microm(2) was identified and found to be distributed evenly across both hemiretinas. Together, these results show that the sampling gain of the ventral retina is significantly greater than the dorsal segment, that retinal specializations important for mediating acute vision are present in the parts of the visual field immediately above and below the surface of the water, and that visual functions related with the large ganglion cells require more even sampling across the visual field. The relevance of these retinal specializations to the feeding and other behavioral strategies adopted by Anableps is discussed.
authors.affiliation: Departamento de Ciências Biologia, Centro de Ciências Biológicas e da Saúde, Universidade Regional do Cariri, URCA, Crato, CE, Brasil.
authors.forename: Francisco Gilberto
authors.initials: FG
authors.lastname: Oliveira
authors.forename: João Paulo
authors.initials: JP
authors.lastname: Coimbra
authors.forename: Elizabeth Sumi
authors.initials: ES
authors.lastname: Yamada
authors.forename: Luciano Fogaça de Assis
authors.initials: LF
authors.lastname: Montag
authors.forename: Francyllena L
authors.initials: FL
authors.lastname: Nascimento
authors.forename: Valéria A
authors.initials: VA
authors.lastname: Oliveira
authors.forename: Diógenes Luís
authors.initials: DL
authors.lastname: da Mota
authors.forename: Alexandre Motta
authors.initials: AM
authors.lastname: Bittencourt
authors.forename: Valdir Luna
authors.initials: VL
authors.lastname: da Silva
authors.forename: Belmira Lara da Silveira Andrade
authors.initials: BL
authors.lastname: da Costa
mesh_terms: D000818:Animals; D002452:Cell Count; D048429:Cell Size; D003532:Cyprinodontiformes / Q000033:anatomy & histology*; D012160:Retina / Q000166:cytology*; D012165:Retinal Ganglion Cells