Anatomy of finfish and shellfish

UNIT 1 - Anatomy of Fin Fish

1.4. Structure of fins
Appendages of fishes comprise of fins and cirrti (flaps of flesh) which attain extreme development in the sargassum fish (pterophryne) and the leafy sea dragan (phyllopteryx). The fins are classified as median or paired.

Median fins (Unpaired fins)
Rayed fins in line with the median axis of a typical fish are these of the back (dorsal fin or fins) the tail (caudal fin) and the lower edge of the body just behind the vent (Anil fin) Although most commonly all of the median fins may be present, but some may be modified or absent in same fishes.
Also developed in the median axis may be a rayless fatty adipose fin (as in the trouts – Salmonidae) off fins reduced to a few disconnected spines as in the stickle backs – Gasterosteidae) The anal fin may be modified into an intermittent organ, the gonopodium for use in copulation (as in the live bearers – Poecilidae).

Paired fins
Paired fins are the Pectorals and Peluics (ventral) the pectorals are supported by the pectoral girdle that joins the skull. Although ordinarily present in fishes, the pectorals are wanting in such kinds as the lamprey (Petromyzonidae) and hag fishes (Myxinidae) They are greatly enlarged in the (Soaring) flying fishes (Exocoetidae) and flying characins (Gastropelecinae). In some cling fishes (Gobiesocidae) and Asiatic suckerbelly loaches (Gastromyzan) the pectorals serve as a part of the ventral hold fast organ.

The pelvic fins vary substantially in position and in adoptive modification typically their support is by a pelvic girdle anchored in the bully musculature.
In soft rayed fishes (Malacopterygians) the peluics are abdominal in position, Eg. Clupeoids, Salmonids, cypriroids, but they also be situated arterially, just below the pectorals in a thoracic position (as in many spiny rayed species, the Acanthopterygians) or even under the throat in a jugular position (as in blennies). The pelvic are lacking in the lampreys and hag fishes and is lost in various other fishes, rlotably the cels (Angullidae etc) In the sharks and some relatives they are modified into claspers. In cling fishes (Gobiorocidae) sucker belly loaches (Gastromyzon) and certain other fishes, the pelvic from part of a hold fast organ that resembles a ruction cup on the belly.