Cyprinodontiformes

Lore & Background

Some members of this order are notable for inhabiting extreme environments, such as saline or very warm waters, heavily polluted waters, rain water pools devoid of minerals and made acidic by decaying vegetation, or isolated situations where no other types of fish occur. They are typically carnivores, and often live near the surface, where the oxygen-rich water compensates for environmental disadvantages. Scheel (1968) observed the gut contents were invariably ants, others have reported insects, worms and aquatic crustaceans. Aquarium specimens are invariably seen eating protozoans from the water column and the surfaces of leaves, however these are not apparent as stomach contents. Many members of the family Cyprinodontidae (the pupfishes) eat plant material as well and some have adapted to a diet very high in algae to the point where one, the Flagfish also known as American flagfish, is a renowned algae eater in the aquarium, in spite of belonging to an order of fishes that do not generally consume any plant material. In addition, killifish derive some of the carotenoids and other chemicals required to make their body pigments from pollen grains on the surface of and in the gut of insects they eat from the surface of the water; this can be simulated in culture by the use of special color enhancing foods that contain these compounds.

Reader's Guide

The Cyprinodontiformes are significant as a diverse order of small freshwater fish that includes many popular aquarium species, such as killifish and live-bearers. Their reproductive strategies are notably varied, encompassing oviparous (egg-laying), ovoviviparous (live birth with eggshell), and viviparous (live birth without eggshell) forms, with vivipary and ovovivipary having evolved independently from oviparous ancestors. The order's fossil record extends to the Late Paleocene, though the oldest known specimen, ?Cyprinodon primulus, is of uncertain taxonomic identity. Ecologically, many species thrive in extreme environments, such as saline waters or acidic pools, and are primarily carnivorous, though some pupfishes consume algae. The largest species, the cuatro ojos, reaches 34 cm, while the smallest, the least killifish, is only 8 mm. The classification includes two suborders: Aplocheiloidei (all oviparous) and Cyprinodontoidei (with both oviparous and live-bearing families). Their legacy lies in their adaptability, reproductive diversity, and importance in the aquarium trade.

Did You Know?

• The colloquial term 'toothcarps' is used for the order, though they are not close relatives of true carps.
• The oldest fossil record is ?Cyprinodon primulus from the Late Paleocene of Argentina, though its exact identity is uncertain.
• The largest species, the cuatro ojos (Anableps dowei), measures 34 cm, while the smallest, the least killifish (Heterandria formosa), is just 8 mm.
• Vivipary and ovovivipary have evolved independently from oviparous ancestors, the latter possibly twice.