Fish school dynamics: characterizing transient formations

Fish schools have long been thought to favor a diamond formation during migration due to reduced fluid drag and hydrodynamic stability, as suggested by Lighthill and Weih. To test this conjecture, we monitored and tracked schools of giant danios (Devario aequipinnatus) for 10 hours under flow conditions. Surprisingly, our observations revealed that fish schools did not settle into any stable formation during the experiments; instead, they continuously rearranged their positions. This finding challenges the notion of self-stabilizing formations in fish schools.