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The operculum is a series of bones found in bony fish and chimaeras that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding. [1]
The opercular series contains four bone segments known as the preoperculum, suboperculum, interoperculum and operculum. The preoperculum is a crescent-shaped structure that has a series of ridges directed posterodorsally to the organisms canal pores. The preoperculum can be located through an exposed condyle that is present immediately under its ventral margin; it also borders the operculum, suboperculum, and interoperculum posteriorly. The suboperculum is rectangular in shape in most bony fish and is located ventral to the preoperculum and operculum components. It is the thinnest bone segment out of the opercular series and is located directly above the gills. The interoperculum is triangular shaped and borders the suboperculum posterodorsally and the preoperculum anterodorsally. This bone is also known to be short on the dorsal and ventral surrounding borders. [2]
During development the opercular series is known to be one of the first bone structures to form. In the three-spined stickleback the opercular series is seen forming at around seven days after fertilization. Within hours the formation of the shape is visible and then the individual components are developed days later. The size and shape of the operculum bone is dependent on the organism's location. For example, fresh water threespine sticklebacks form a less dense and smaller opercular series in relation to marine threespine sticklebacks. The marine threespine stickleback exhibits a larger and thicker opercular series. This provides evidence that there was an evolutionary change in the operculum bone. The thicker and more dense bone may have been favored due to selective pressures exerted from the threespine stickleback's environment. The development of the operculuar series has changed dramatically over time. The fossil record of the threespine stickleback provide the ancestral shapes of the operculum bone. Overall, the operculum bone became more triangular in shape and thicker in size over time. [2]
Genes that are essential in the development of the opercular series include the Eda and Pitx1 genes. These genes are known to be a part of the development and loss of armor plates in gnathostomes. The Endothelin1 pathway is thought to be associated with the development of the operculum bone since it regulates dorsal-ventral patterning of the hyomandibular region. Mutations in the Edn1-pathway in zebrafish are known to lead to deformities of the opercular series' shape and size. [2]
The opercular series is vital in obtaining oxygen. They open as the mouth closes, causing the pressure inside the fish to drop. Water then flows towards the lower pressure across the fish's gill lamellae, allowing some oxygen to be absorbed from the water. Cartilaginous ratfishes (chimaeras) possess soft and flexible opercular flaps. Sharks, rays and relatives among elasmobranch fishes lack the opercular series. They instead respire through a series of gill slits that perforate the body wall. Without the operculum bone, other methods of getting water to the gills are required, such as ram ventilation, as used by many sharks.
Chondrichthyes is a class of jawed fish that contains the cartilaginous fish or chondrichthyians, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or bony fish, which have skeletons primarily composed of bone tissue. Chondrichthyes are aquatic vertebrates with paired fins, paired nares, placoid scales, conus arteriosus in the heart, and a lack of opecula and swim bladders. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.
A gill is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are kept moist. The microscopic structure of a gill presents a large surface area to the external environment. Branchia is the zoologists' name for gills.
Fish anatomy is the study of the form or morphology of fish. It can be contrasted with fish physiology, which is the study of how the component parts of fish function together in the living fish. In practice, fish anatomy and fish physiology complement each other, the former dealing with the structure of a fish, its organs or component parts and how they are put together, such as might be observed on the dissecting table or under the microscope, and the latter dealing with how those components function together in living fish.
Aquatic respiration is the process whereby an aquatic organism exchanges respiratory gases with water, obtaining oxygen from oxygen dissolved in water and excreting carbon dioxide and some other metabolic waste products into the water.
Gasterosteoidei is a suborder of ray-finned fishes that includes the sticklebacks and relatives, the 5th edition of Fishes of the World classifies this suborder within the order Scorpaeniformes.
The three-spined stickleback is a fish native to most inland and coastal waters north of 30°N. It has long been a subject of scientific study for many reasons. It shows great morphological variation throughout its range, ideal for questions about evolution and population genetics. Many populations are anadromous and very tolerant of changes in salinity, a subject of interest to physiologists. It displays elaborate breeding behavior and it can be social making it a popular subject of inquiry in fish ethology and behavioral ecology. Its antipredator adaptations, host-parasite interactions, sensory physiology, reproductive physiology, and endocrinology have also been much studied. Facilitating these studies is the fact that the three-spined stickleback is easy to find in nature and easy to keep in aquaria.
Chimaeras are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively.
Bothriolepis was a widespread, abundant and diverse genus of antiarch placoderms that lived during the Middle to Late Devonian period of the Paleozoic Era. Historically, Bothriolepis resided in an array of paleo-environments spread across every paleocontinent, including near shore marine and freshwater settings. Most species of Bothriolepis were characterized as relatively small, benthic, freshwater detritivores, averaging around 30 centimetres (12 in) in length. However, the largest species, B. rex, had an estimated bodylength of 170 centimetres (67 in). Although expansive with over 60 species found worldwide, comparatively Bothriolepis is not unusually more diverse than most modern bottom dwelling species around today.
This glossary of ichthyology is a list of definitions of terms and concepts used in ichthyology, the study of fishes.
The prickly dogfish is a poorly known species of dogfish shark in the family Oxynotidae, inhabiting temperate Australian and New Zealand waters. Reaching a length of 75 cm (30 in), this brown to gray shark has a very thick body with a prominent "humpback" and extremely rough skin. It is further characterized by two enormous, sail-like dorsal fins placed relatively close together. Both dorsal fins have a spine embedded mostly within the fleshy leading portion of the fin; the first dorsal spine is tilted forward.
The Izak catshark or simply Izak is a species of catshark, belonging to the family Scyliorhinidae, common off the coasts of South Africa and southern Namibia. It typically inhabits the outer continental shelf at depths of 100–300 m (330–980 ft), with the males found deeper than the females and juveniles. The Izak catshark has a short, wide, flattened head and a robust body tapering to a long, slender tail. It can be identified by its ornate color pattern of dark brown spots or reticulations and blotches on a light yellowish background, as well as by the enlarged dermal denticles over its pectoral fins and along its dorsal midline from the snout to the second dorsal fin. This species reaches 69 cm (27 in) in length, with the males larger than females.
Haploblepharus is a genus of catshark, and part of the family Scyliorhinidae, containing four species of shysharks. Their common name comes from a distinctive defensive behavior in which the shark curls into a circle and covers its eyes with its tail. The genus is endemic to southern Africa, inhabiting shallow coastal waters. All four species are small, stout-bodied sharks with broad, flattened heads and rounded snouts. They are characterized by very large nostrils with enlarged, triangular flaps of skin that reach the mouth, and deep grooves between the nostrils and the mouth. Shysharks are bottom-dwelling predators of bony fishes and invertebrates. They are oviparous, with the females laying egg capsules. These harmless sharks are of no commercial or recreational interest, though their highly limited distributions in heavily fished South African waters are of potential conservation concern.
The mouse catshark is a species of catshark and part of the family Scyliorhinidae. It is common in the northeastern Atlantic Ocean from Iceland to Western Sahara. There is much taxonomic confusion regarding this species in Icelandic waters, where it may be confounded with another species of Galeus or Apristurus. Probably not exceeding 49 cm (19 in) long, the mouse catshark has a uniformly brown body and is characterized by large, rounded pelvic fins and crests of enlarged dermal denticles along both the dorsal and ventral caudal fin margins. In addition, in adult males the inner margins of the pelvic fins are merged into an "apron".
The African sawtail catshark is a species of catshark, part of the family Scyliorhinidae. Demersal in nature, it is found at depths of 160–720 m (520–2,360 ft) off the western African coast from Morocco to South Africa. This slender species has a rather long, pointed snout, a series of dark saddles along the back and tail, and a prominent crest of enlarged dermal denticles along the upper edge of the caudal fin. Its maximum known length is 46 cm (18 in).
Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the gills. As gills are the primitive condition of vertebrates, all vertebrate embryos develop pharyngeal arches, though the eventual fate of these arches varies between taxa. In jawed fish, the first arch develops into the jaws. The second gill arch develops into the hyomandibular complex, which supports the back of the jaw and the front of the gill series. The remaining posterior arches support the gills. In amphibians and reptiles, many elements are lost including the gill arches, resulting in only the oral jaws and a hyoid apparatus remaining. In mammals and birds, the hyoid is simplified further.
Polonosuchus is a genus of rauisuchid known from the late Triassic of Poland. It was a huge predator about 5–6 metres in length and, like all rauisuchians, was equipped with a large head of long sharp teeth. The legs were placed almost underneath the body, unlike most reptiles, which would have made it quite fast and a powerful runner. The appearance was very similar to that of the more known Postosuchus, of North America, and shared with the latter the ecological niche of the apex predator.
Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the spine and are supported only by muscles.
Fish gills are organs that allow fish to breathe underwater. Most fish exchange gases like oxygen and carbon dioxide using gills that are protected under gill covers (operculum) on both sides of the pharynx (throat). Gills are tissues that are like short threads, protein structures called filaments. These filaments have many functions including the transfer of ions and water, as well as the exchange of oxygen, carbon dioxide, acids and ammonia. Each filament contains a capillary network that provides a large surface area for exchanging oxygen and carbon dioxide.
Fish physiology is the scientific study of how the component parts of fish function together in the living fish. It can be contrasted with fish anatomy, which is the study of the form or morphology of fishes. In practice, fish anatomy and physiology complement each other, the former dealing with the structure of a fish, its organs or component parts and how they are put together, such as might be observed on the dissecting table or under the microscope, and the later dealing with how those components function together in the living fish. For this, at first we need to know about their intestinal morphology.
Qilinyu is a genus of early placoderm from the late Silurian of China. It contains a single species, Qilinyu rostrata, from the Xiaoxiang fauna of the Kuanti Formation. Along with its contemporary Entelognathus, Qilinyu is an unusual placoderm showing some traits more similar to bony fish, such as dermal jaw bones and lobe-like fins. It can be characterized by adaptations for a benthic lifestyle, with the mouth and nostrils on the underside of the head, similar to the unrelated antiarch placoderms. The shape of the skull has been described as "dolphin-like", with a domed cranium and a short projecting rostrum.
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