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The photoreceptor system in the retinae of two dogfishes, Scyliorhinus canicula and Galeus melastomus : possible relationship with depth distribution and predatory lifestyle
Author(s) -
Bozzanao A.,
Murgia R.,
Vallerga S.,
Hirano J.,
Archer S.
Publication year - 2001
Publication title -
journal of fish biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.672
H-Index - 115
eISSN - 1095-8649
pISSN - 0022-1112
DOI - 10.1111/j.1095-8649.2001.tb00190.x
Subject(s) - scyliorhinus canicula , biology , retinal , anatomy , retina , interspecific competition , zoology , fish <actinopterygii> , ecology , botany , fishery , neuroscience
The small spotted dogfish Scyliorhinus canicula and the blackmouth dogfish Galeus melastomus , whose depth distributions overlap in the upper part of the slope ( c . 500 m depth), where they have access to the same prey community, have well‐developed eyes and a pure‐rod retina with a single layer of photoreceptors. Interspecific differences in rod outer segment length ( L ROS ) within retinal regions were found. In the periphery and the retinal centre G. melastomus showed a L ROS 24 and 30% longer, respectively, than S. canicula and, therefore, a potential for increased sensitivity. In both species longer L ROS were always found in correspondence with the retinal centre where the ganglion cell topography formed a horizontal meridian that allowed for better discrimination of the horizon in the visual field. In this area L ROS reached 53·4±4·1μm in S. canicula and 77·1±10·5μm in G. melastomus against 46·3±4·2μm and 61·1±10·1μm in the retinal periphery. No significant differences were recorded in L ROS and rod density during growth. In both species, a rapid increase of theoretical visual acuity was found to be related to an increase in fish L T and lens size. Visual acuity ranged between 1·7 and 3 cycles degree ‐1 in S. canicula and 2·4 and 4·2 in G. melastomus . The G. melastomus rod visual pigment showed the characteristic spectral adaptation to vision in deep‐water (λ max of 481 nm), but was also well placed to detect the bioluminescence of some of its main prey species. In S. canicula the visual pigment absorption (λ max of 496 nm) was more typical of shallow water living fishes. The opsin sequences of the two visual pigments are discussed and key amino acid sites were identified where sequence changes could be responsible for the spectral absorption differences between the two species. The possible relationship between L ROS , visual acuity, visual pigment absorption, depth distribution and feeding behaviour are discussed.