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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 dorsal fin originates from above the (relatively large) eyes and runs the entire length of the fish. Of the approximately 400 dorsal fin rays, the first 10 to 13 are elongated to varying degrees, forming a trailing crest embellished with reddish spots and flaps of skin at the ray tips. The pelvic fins are similarly elongated and adorned ...
The illicium is the detached and modified first three spines of the anterior dorsal fin. In most anglerfish species, the longest filament is the first. This first spine protrudes above the fish's eyes and terminates in an irregular growth of flesh (the esca), and can move in all directions.
Their gill covers have no spines and are covered with small scales. Their two dorsal fins are widely separated, with the anterior fin having five spines, and the posterior fin having one spine and nine soft rays. The posterior dorsal fin is similar in size to the anal fin and is situated above it.
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 ...
The sucking disc begins to show when the young fish are about 1 cm (0.4 in) long. When the remora reaches about 3 cm (1.2 in), the disc is fully formed and the remora can then attach to other animals. The remora's lower jaw projects beyond the upper, and the animal lacks a swim bladder. [9] Some remoras associate with specific host species.
The large pectoral fins are normally carried horizontally, perhaps helping the fish attain the profile of a shark. The first dorsal fin has six to nine independent, short, stout, sharp spines. The family name Rachycentridae, from the Greek words rhachis ("spine") and kentron ("sting"), was inspired by these dorsal spines. The mature cobia has a ...