Three-dimensional schools in nature may have additional mechanisms to enhance individual swimming performance, such as tip vortices shed by pectoral fins. Conducting experimental work on schooling fish is challenging and empirical evidence supporting the maintenance of a diamond formation has been conflicting. Respirometry measurements remain
difficult owing to the mutually exclusive requirements of having a large working area to minimize wall effects and behavioural abnormalities, and having a small water volume necessary for accurate oxygen measurements. With these precautions in mind, the metabolic cost of an individual swimming in a school has been estimated to be less than for an individual swimming in solitude based on reduced tail-beat frequencies.