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The shape, size, position and colour of the dorsal fin varies with the type of billfish, and can be a simple way to identify a billfish species. For example, the white marlin has a dorsal fin with a curved front edge and is covered with black spots. [4] The huge dorsal fin, or sail, of the sailfish is kept retracted most of the time. Sailfish ...
A fish can have up to three dorsal fins. The dorsal fins serve to protect the fish against rolling, and assist it in sudden turns and stops. In anglerfish, the anterior of the dorsal fin is modified into an illicium and esca, a biological equivalent to a fishing rod and lure; The bones that support the dorsal fin are called pterygiophores.
Dorsal fins: Located on the back of the fish, dorsal fins serve to prevent the fish from rolling and assist in sudden turns and stops. Most fishes have one dorsal fin, but some fishes have two or three. In anglerfish, the anterior of the dorsal fin is modified into an illicium and esca, a biological equivalent to a fishing rod and lure.
The caudal fin is homocercal, meaning the upper and lower lobes are about equal in size. The spine ends at the caudal peduncle, the base of the caudal fin, distinguishing this group from those in which the spine extends into the upper lobe of the caudal fin, such as most fish from the Paleozoic (541 to 252 million years ago). The neural arches ...
The anal fin contains 1–4 spines anteriorly and 20–39 soft rays with their height, direction, origin, and terminus mirroring those of the soft dorsal fin. Along the belly are a series of spinous scutes—scales modified into hard, bony plates—forming an armoured ventral keel. Similar scutes also cover the base of the dorsal and anal fins.
The mouth is reddish at the corners where there are small barbels. When breeding the mature males develop a red stripe along the sides [3] on the belly, mouth, gill cover and pectoral fin base. The dorsal fin and the anal fin each have 8 soft rays and the lateral line has 66–84 scales. They can grow to 36 centimetres (14 in) in total length.
This gives the dorsal and anal fins a noticeably scythe-like shape. [3] The dorsal fin of the lookdown has 9 spines and 23 rays, while the anal fin has only 3 spines and 18 rays. [4] Like the Atlantic moonfish, it has a deep, rhombus-shaped, laterally-compressed body. [3] The head has the mouth set low and the eyes high.
Furthermore, the rudd's number of soft rays in the dorsal fin (8–9 compared to 10–12). There can be confusion with the ide also, which has smaller scales however. There is a variety of the common rudd, popular among pond -keepers, known as the golden rudd , which has a gold-coloured body.