The story
From flag + fish. The red, white and blue stripes and dots are reminiscent of the American flag.
Etymology from Wiktionary, CC BY-SA 4.0.
flagfish
Today it means: A freshwater fish in the family Cyprinodontidae native to Florida, Jordanella floridae, sometimes kept in aquaria and used in laboratory tests of the biological effects of environmental pollutants. Full definition →