Choroidal rete mirabile function and resistance to retinal oxygen toxicity in fish

Previous studies have suggested that resistance to O2 toxicity in teleost fish retina is directly related to choroidal rete mirabile function and to the chronically elevated PO2 at the retina. We tested this hypothesis in several species of fish with varying degrees of rete development. The effect of hyperbaric oxygen on O2 consumption, Na+-, K+-ATPase activity nd the ERG was recorded. Hyperbaric oxygen had no effect on the ERG of either the flounder, which has a large rete and elevated PO2, or the eel, which has no rete. Exposure to hyperbaric oxygen for 6 hr attenuated by 50% the ERG of the goosefish which has a small rete (retinal PO2 = 90 mmHg). Hyperbaric oxygen abolished the b-wave of the dogfish ERG and attenuated the skate b-wave by 80%. Elasmobranchs have no rete and low retinal PO2. Hyperbaric oxygen had no effect on O2 consumption and ATPase activity in any species studied. The ERG data supported the hypothesis that resistance to oxygen toxicity by the teleost retina is an adaptation to a chronically elevated PO2 generated by the choroidal rete.