Determination of the development rate of the choroid rete, the visual behaviour, the effect of stress on visual behaviour and the metabolice response of two Antarctic fish to exercise stress

In Antarctic fish, retinal function is critically dependent on oxygen supply and in some fishes additional oxygen can be unloaded through a choroid rete at the back of the retina. The relative development of the choroid rete in two species of Antarctic fish: Pagothenia borchgrevinki and Trematomus bernacchii was examined. Such fishes also have "Root Effect" haemoglobins which can release additional oxygen at low pH; the rete lowers pH locally, promoting release of oxygen and maintaining visual function. The visual acuity of Antarctic fish species, using the optomotor response (movement of the fish to follow a moving visual background) was determined. Intense exercise, producing lactic acid, can lower pH in other tissues and interfere with the localised oxygen release in the rete. Thus Root effect, choroid rete and stress may all interact. The effects of stress on visual acuity was measured and the metabolic response of Antarctic fishes to exercise stress was characterised by behavioural experiments.