Visual Function in Four Antarctic Nototheniid Fishes

• Main Authors: PANKHURST, N. W., MONTGOMERY, J. C.
• Format: Text
• Language: English
• Published: Company of Biologists 1989
• Subjects: Journal Articles; Antarctic; The Antarctic; Antarc*
• Online Access: http://jeb.biologists.org/cgi/content/short/142/1/311

Visual function was investigated in the antarctic fish Pagothenia borchgrevinki (Boulenger), Trematomus bernacchii Boulenger, T. centronotus Regan and T. hansoni Boulenger. All Trematomus species have large anterior aphakic spaces (indicating a forward feeding vector), whereas Pagothenia does not. Pagothenia and T. hansoni , which both feed in the water column, lack the corneal iridescence displayed by T. bernacchii and T. centronotus . This is thought to relate to the importance of downwelling light for image formation in Pagothenia and T. hansoni . Absolute sensitivity thresholds to white and monochromatic light were measured using electroretinogram (ERG) responses in light- and dark-adapted Pagothenia and dark-adapted Trematomus species. Dark-adapted fish (retinal screening pigment withdrawn from rod outer segments) had thresholds of l.3x10-3µEm-2s-1 to a 200ms pulse of white light, whereas that of lightadapted Pagothenia (rod outer segments covered by the retinal screening pigment) was l.9x10-2µEm-2s-1. We suggest that the thresholds approximate threshold stimuli for rods and cones, respectively. Measurement of thresholds of light-adapted Pagothenia made using a behavioural measure (feeding responses) gave a threshold of 5x10-3µEm-2s-1. Limits for photopic and scotopic vision are predicted to be reached at depths of 20-40 and 30-60 m, respectively, under snow and ice conditions typically encountered at this time of year. ERG-determined spectral sensitivity curves peaked around 500 nm in all four species and matched the spectral irradiance under the ice. Shifts to longer wavelengths in spectral irradiance caused by sub-ice phytoplankton growth may degrade visual ability. Flicker fusion frequencies (FFFs) reached a maximum value of 15 Hz in Pagothenia at the maximum stimulus intensity used, but at environmentally realistic light intensities they were less than 8 Hz. FFFs were lower in all Trematomus species than in Pagothenia .