A small, brightly colored tropical freshwater fish popular in aquariums; also a prefix meaning four.
From Greek tetra- meaning 'four,' referring to the characteristic four-part structure of their fins. The fish name became popular in the aquarium trade in the mid-20th century.
Tetra fish are masters of schooling behavior - they move in synchronized groups that create mesmerizing patterns in aquariums. Their name connects them to the mathematical perfection of the number four, which appears throughout nature in crystal structures, flower petals, and molecular arrangements.
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