Anal fin – a single fin on the midline of the lower or ventral surface of a fish, just before the tail and usually just behind the anus and urogenital openings

Caudal fin – tail of fishes and some other aquatic vertebrates, used for forward motion

Fish – any of three classes (jawless, cartilaginous and bony) of cold-blooded vertebrate animals living in water and having fins, permanent gills for breathing, and, usually, scales

Gills – membranes fish use to absorb dissolved oxygen from the water during respiration

Ichthyology – branch of zoology dealing with fishes

Lateral line – horizontal lines of sensors along the head and sides of fishes and some amphibians used to locate water current and pressure changes, vibrations, food, other fish and dangers

Pectoral fin – anterior pair of fins attached to the pectoral girdle of fishes, corresponding to the forelimbs of higher vertebrates

Pelvic fin – fin on each side of the belly of most fish, used for positioning and balance

Soft dorsal fin – soft-rayed vertical fin on the top of most fish, used for balance and to move in tight spaces

Spiny dorsal fin – hard-rayed vertical fin on the top of many fish, used for balance, defense and to move in tight spaces

Swim bladder – an air-filled structure in many fishes that maintains buoyancy or, in some species, helps in respiration; also called air bladder