cyprinodontiform

Cyprinodontiformes is an order of ray-finned fishes (Actinopterygii) that includes a diverse array of small to medium-sized species found in freshwater and brackish environments. Members of this group are commonly referred to as killifish and livebearers, and several lineages are important in the aquarium trade as well as in ecological and evolutionary studies. Representative families include Poeciliidae (livebearers such as guppies, mollies, platies, and swordtails), Fundulidae (killifishes), Goodeidae, Cyprinodontidae (pupfishes), and related groups.

Ecology and distribution vary across the order. Cyprinodontiforms inhabit a wide range of habitats, from tropical rivers and coastal lagoons to temporary ponds in arid regions. They are especially diverse in the Americas, with many species adapted to fluctuating water levels and brackish conditions. Some killifishes lay eggs that can survive dry periods, enabling life cycles in ephemeral waters, while many Poeciliidae are livebearers, giving birth to relatively developed young.

Reproduction and morphology show notable diversity within Cyprinodontiformes. Species range from elongated, colorful fishes kept by hobbyists to small, cryptic forms adapted to harsh environments. Physical characteristics such as fin shapes and color patterns often reflect ecological niches and reproductive strategies. This diversity has made cyprinodontiforms a focal point for studies in evolution, speciation, and adaptation.

Conservation and human use: Several species face habitat loss and environmental change. Many are widely kept in aquariums, contributing to captive breeding programs, while others are protected in the wild due to their limited ranges or declining populations.