Post #3872914

"In several countries, animal welfare regulations ban fish keeping in spherical aquaria. A reason for this is the belief that fish behaviour is adversely affected in spherical aquaria, because the light refraction at the aquarium's wall severely disrupts the image of the aerial world, which may disturb the fish. Using analytical calculations and geometric optical ray-tracing, we determined the paths of light rays originating from various locations in water-filled spherical and cubic aquaria to the surrounding aerial target space, in order to find out which aquarium causes greater angular refraction distortions of the aerial world perceived by fishes. We found that if a fish is not in the aquarium's centre, there are always viewing directions where either the spherical or the cubic aquarium's wall causes greater refraction distortions. However, depending on the fish's position in the aquarium, a cubic aquarium causes greater fish-perceived refraction distortions of the aerial world in 2–9 times larger angular volume than a spherical aquarium. This finding is corroborated by optical demonstrations of the refraction distortion of an aerial quadratic grid seen from water-filled spherical and cubic aquaria. We conclude that there is not an optical basis for the prohibition of fish keeping in spherical aquaria." #aquariums https://royalsocietypublishing.org/rspa/article/482/2342/20260024/482525/Viewing-the-aerial-world-from-water-filled