Electroretinograms, retina analysis, behavioural observations and gut content and clearance rate of notothenioid Antarctic fish to determine the importance of visual function in feeding

The visual function in Pagothenia borchgrevinki was investigated in relation to their feeding by relating feeding with the vertical stratification of zooplankton and then determining their visual sensitivity and the environmental light levels to assess the relative importance of visual and non-visual sensory systems in feeding. Recordings of the electroretinograms (ERG - the electrical response of the retina to imposed light flashes) were made on 30 specimens with the absolute threshold for the ERG, and spectral properties of the response determined and the tucker-fusion rate determined to assess cone thresholds. The response of adult male, adult female and pre adult fish were compared. Retina material was fixed for histological determination of retinal parameters. Behavioural observations were made using an infra-red video system to determine the visual threshold for feeding. Gut clearance rates were determined where on 4 occasions large (>50) samples of fish were caught and subsamples sacrificed at successive 6 hourly intervals to measured gut clearance rate. The visual function in three benthic species of Antarctic fish (Trematomus bernacchii, T. hansoni and T. contronotus) was investigated with ERG's recorded, gut contents analysed and morphological and histological studies of the eyes completed to compare with their dietary preferences to assess the role of vision in feeding.