µCT image of a perch (Perca fluviatilis) eye.

Despite the high metabolic demands on the retina, the teleost retinas are not vascularised, where oxygen is delivered by generation of a very high pO₂. This can only be achieved by possession of Root effect hemoglobins and a choroid rete mirabili. However, previous studies have shown secondary reductions in the Root effect magnitude in teleost fish hemoglobins as well as loss of the choroid rete mirabili, leaving the question of how these groups of fishes supply oxygen to the retina. Such species include the European eel and striped catfish, which have hemoglobin with a reduced Root effect and have developed retinal capillarization to maintain retinal oxygenation. Thus, the present study aims to investigate how secondary reductions in Root effect magnitude shape the vasculature in the eye.