Sea turtles use their powerful flippers to propel themselves. Sea lions rely upon their powerful fore flippers to gain thrust while using their rear flippers as a rudder. In contrast, seals acquire their thrust by using their strong rear flippers. Some types of fast-swimming fish have a horizontal caudal keel just forward of the tail fin. Much like the keel of a ship, this is a lateral ridge on the caudal peduncle, usually composed of scutes (see below), that provides stability and support to the caudal fin. There may be a single paired keel, one on each side, or two pairs above and below. Icardo, José M. (2006). "Conus arteriosus of the teleost heart: Dismissed, but not missed". The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology. 288A (8): 900–908. doi: 10.1002/ar.a.20361. ISSN 1552-4884. PMID 16835938. S2CID 9676359. Ichthyosaurs are ancient reptiles that resembled dolphins. They first appeared about 245million years ago and disappeared about 90million years ago.

In terms of spermatogonia distribution, the structure of teleost testes have two types: in the most common, spermatogonia occur all along the seminiferous tubules, while in Atherinomorpha, they are confined to the distal portion of these structures. Fish can present cystic or semi-cystic spermatogenesis [ definition needed] in relation to the release phase of germ cells in cysts to the lumen of the seminiferous tubules. [50] Ovaries [ edit ] Aristotle, De incessu animalium [74] Comparison between A) the swimming fin of a lobe-finned fish and B) the walking leg of a tetrapod. Bones considered to correspond with each other have the same color. In a parallel but independent evolution, the ancient reptile † Ichthyosaurus communis developed fins (or flippers) very similar to fish (or dolphins). In conclusion, the rounded tail is a helpful characteristic for fish identification. However, other physical features should also be considered. Forked TailSo, by looking at tail shape and other physical features, it’s possible to correctly identify fish species. Rounded Tail

By looking at the fins and tail, as well as other features such as scales, body depth, and mouth shape, you can identify the fish species. Other features like Cycloid scales, ganoid scales, and cosmoid scales, protective spines, chromatophores, iridocytes, and bioluminescence can also be useful. Identifying Fish Species by Dorsal, Anal, Pelvic and Pectoral Fins A similar renovation of an old theory may be found in the developmental programming of chondricthyan gill arches and paired appendages. In 2009, researchers at the University of Chicago demonstrated that there are shared molecular patterning mechanisms in the early development of the chondricthyan gill arch and paired fins. [68] Findings such as these have prompted reconsideration of the once-debunked gill-arch theory. [65] From fins to limbs [ edit ]Dorsal fin: This is the fin on the top of the fish, behind the head. Notice its origin (where it connects to the body) to identify the species. Trout’s dorsal fin origin is in the middle of the body. The skin of the fish are a part of the integumentary system, which contains two layers: the epidermis and the dermis layer. The epidermis is derived from the ectoderm and becomes the most superficial layer that consists entirely of live cells, with only minimal quantities of keratin. It is generally permeable. The dermis is derived from the mesoderm and resembles the little connective tissue which are composed of mostly collagen fibers found in bony fish. Some fish species have scales that emerge from the dermis, penetrate the thin layer of the basement membrane that lies between the epidermis and dermis, and becomes externally visible and covers the epidermis layer. [19]