Cyprinodontiforms

Cyprinodontiformes is an order of ray-finned fishes (Actinopterygii) within the superorder Atherinomorphae. The group is diverse, ranging from small to medium-sized species, and includes both egg-laying and live-bearing taxa. Cyprinodontiforms occupy freshwater and brackish habitats in tropical and subtropical regions, with a strong presence in the Americas and Africa and a number of Old World lineages in Africa and parts of Asia.

Taxonomy and diversity: The order comprises several families, including Cyprinodontidae (pupfishes), Fundulidae (fundulids), Profundulidae (topminnows), Poeciliidae (livebearers such as guppies, mollies, swordtails and platies), and killifish families such as Aplocheilidae and Nothobranchiidae. Taxonomic placement has varied with different classifications, reflecting substantial diversity and rapid speciation.

Habitat and ecology: Many cyprinodontiforms are adapted to ephemeral or variable environments, such as temporary ponds, springs, and streams, sometimes with brackish water. Annual species in temporary ponds often have rapid life cycles and drought-resistant eggs, while others persist in more stable waters.

Reproduction and biology: Egg-laying cyprinodontiforms generally broadcast or guard eggs, whereas Poeciliidae are typically live-bearers with internal fertilization. Sexual dimorphism is common, with males often more colorful or elaborately finned. Reproductive modes and parental care vary across lineages.

Significance: Cyprinodontiforms are popular in the aquarium trade (notably guppies, swordtails, mollies, and platies) and have long been used in evolutionary and ecological research, including studies of speciation, sexual selection, and adaptation to ephemeral habitats.