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Goldfish may seem like simple creatures swimming in a glass tank, but they possess a rather complicated navigation system, as discovered by researchers at the University of Oxford Led by Dr. Adelaide Sibeaux, the study aims to shed light on our understanding of how fish, and potentially humans, estimate distances using what could be described as an internal GPS.

Writing in the journal Proceedings of the Royal Society B, Sibeaux and colleagues report how they created a tank in their experiment with 2cm-wide black and white vertical stripes (条纹) on the walls, connected by similar stripes across the floor. The team trained nine goldfish to swim a set distance of 70cm and then return to their starting point when waved at. The experiment aimed to investigate how the fish would estimate this distance without any gestures, under different patterns.

Over multiple trials, the goldfish averaged a swim distance of 74cm, give or take 17cm, when presented with the vertical 2cm-wide stripes. However, when the stripe pattern was altered to either narrower vertical stripes, checked patterns, or horizontal stripes, the fish’s behavior changed significantly. Narrower vertical stripes led them to overestimating the distance by 36%, while horizontal stripes resulted in highly inconsistent estimations.

According to the researchers, the goldfish appeared to be using an “optic (光学的) flow mechanism” based on the visual density of their environment. They kept track of how frequently the vertical pattern switched between black and white to estimate how far they had traveled. The study suggests that different optic flow mechanisms are used by mammals, including humans, based on angular (有角度的) motion of visual features. The study implies that the use of visually based distance information could have emerged early in the evolutionary timeline.

“This study is novel because, despite knowing that fish respond to geometric information regarding direction and distance, we don’t know how they estimate distances,” Professor Colin Lever, although not involved in the study, said, “it’s exciting to explore fish spatial mapping because fish navigation evolved earlier and better than most mammals.”