medianfin

Medianfin is a term used to describe the unpaired fins located along the midline of the body in aquatic vertebrates. In fishes, median fins commonly include the dorsal fins along the back, the anal fin on the ventral side near the tail, the caudal fin forming the tail, and, in some lineages, the adipose fin behind the dorsal fin. Median fins are distinguished from paired fins, which arise in bilateral pairs (pectoral and pelvic fins) and often contribute differently to movement and stability.

The number, position, and shape of median fins vary across taxa. Dorsal fins may be single or multiple; the anal fin is present in many species but can be reduced or absent in others; the caudal fin is typically the main source of propulsion and can differ in morphology among species. In some teleosts, an adipose fin is a small, fleshy fin located between the dorsal and caudal fins; the adipose fin is absent in many groups, and its homology and function are debated.

Functionally, median fins contribute to stability, maneuverability, and thrust. The dorsal and anal fins help reduce rolling and assist with directional control, while the caudal fin provides primary propulsion. Adipose fins, when present, may have sensory or subtle hydrodynamic roles, but their exact function is species-specific and not universal.

Development and evolution: During embryonic development, median fins often arise from a continuous median fin fold along the body's midline, which can segment and ossify into discrete fins in some lineages. Median fins show considerable diversification across fishes, reflecting different ecological demands. Some lineages lose or modify certain median fins, while others retain a full complement as part of their body plan.