| Bony fish Temporal range: 420–0 Ma |
|
|---|---|
| Atlantic herring | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| clade: | Craniata |
| Subphylum: | Vertebrata |
| Infraphylum: | Gnathostomata |
| Superclass*: | Osteichthyes Huxley, 1880 |
| Classes | |
Osteichthyes ( /ˌɒstiːˈɪkθi.iːz/), also called bony fish, are a taxonomic group of fish that have bony, as opposed to fish with cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species. It is the largest class of vertebrates in existence today. Osteichthyes is divided into the ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). The oldest known fossils of bony fish are about 420 million years ago, which are also transitional fossils, showing a tooth pattern that is in between the tooth rows of sharks and bony fishes.[1]
In most classification systems the Osteichthyes are paraphyletic with land vertebrates. That means that the nearest common ancestor of all Osteichthyes includes tetrapods amongst its descendants. Actinopterygii (ray-finned fish) are monophyletic, but the inclusion of Sarcopterygii in Osteichthyes causes Osteichthyes to be paraphyletic. Paradoxically, Sarcopterygii is considered monophyletic, as it includes tetrapods.
Most bony fish belong to the ray-finned fish (Actinopterygii); there are only eight living species of non-tetrapod lobe-finned fish (Sarcopterygii), including the lungfish and coelacanths.
Traditionally, the bony fish had been treated as a class within the vertebrates, with Actinopterygii and Sarcopterygii as subclasses. However, some recent works have elevated Osteichthyes to superclass, with Actinopterygii and Sarcopterygii as classes.
Contents |
Osteichthyans are characterized by a relatively stable pattern of cranial bones, rooted, medial insertion of mandibular muscle in lower jaw. The head and pectoral girdles are covered with large dermal bones. The eyeball is supported by a sclerotic ring of four small bones, but this characteristic has been lost or modified in many modern species. The labyrinth in the inner ear contains large otoliths. The braincase, or neurocranium, is frequently divided into anterior and posterior sections divided by a fissure.
Bony fish typically have swim bladders, which helps the body create a neutral balance between sinking and floating. However, these are absent in many species, and have developed into primitive lungs in the lungfishes. They do not have fin spines, but instead support the fin with lepidotrichia (bone fin rays). They also have an operculum, which helps them breathe without having to swim.
They also are able to see in colour, unlike most other fish.
Bony fish have no placoid scales. Mucous glands coat the body. Most have scales of sort: ganoid, cycloid, or cytenoid. These scales are smooth and overlapping.
The skeleton is made of bone and cartilage, and is almost completely calcified. The vertebral column, cranium, jaw, ribs, and intramuscular bones make up the skeleton.
One of the best-known innovations of the osteichthyans is endochondral bone or "replacement" bone, which is bone ossified internally, by replacement of cartilage, as well as perichondrally, as "spongy bone." In vertebrates, in general, there are various types of calcified tissue: dentine, enamel (or "enameloids") and bone, plus variants characterized by their ontogeny, chemistry, form and location. But endochondral bone is unique because it begins life as cartilage.
In lower vertebrates, cartilaginous structures can become superficially calcified. However, in osteichthyans, the circulatory system invades the cartilaginous matrix. This permits the local osteoblasts (bone-forming cells) to continue bone formation within the cartilage and also recruits additional, circulating osteoblasts. Other cells gradually eat away at the surrounding cartilage. The net result is that the cartilage is replaced from within by a somewhat irregular vascularized network of bone. Structurally, the effect is to create a relatively lightweight, flexible, "spongy" bone interior, surrounded by an outline of dense, lamellar periostial bone. Since this bone now surrounds other bone, rather than cartilage, it is referred to as periostial rather than perichondral. This is the unique endochondral bone from which the osteichthians derived their name, as well as many structural advantages. However useful endochondral bone may be, it is also much heavier and less flexible than cartilage. Thus, many modern osteichthyan groups, including the extremely successful teleosts, have evolved away from extensive use of endochondral bone.
All bony fish possess gills. For the majority this is their sole or main means of respiration. Lungfish and other osteichthyan species are capable of respiration through lungs or vascularized swim bladders. Other species can respire through their skin, intestines, and/or stomach.[2]
Osteichthyes are primatively ectothermic (cold blooded), meaning that their body temperature is dependent on that of the water. But some members of the family scombridae such as the swordfish and tuna have achieved various levels of endothermy. They can be any type of heterotroph: omnivore, carnivore, herbivore, or detritivore.
Some bony fish are hermaphrodites, and a number of species exhibit parthenogenesis. Fertilization is usually external, but can be internal. Development is usually oviparous (egg-laying) but can be ovoviviparous, or viviparous. Although there is usually no parental care after birth, before birth parents may scatter, hide, guard or brood eggs, with sea horses being notable in that the males undergo a form of 'pregnancy', brooding eggs deposited in a ventral pouch by a female.
The ocean sunfish is the largest bony fish in the world, while the longest is the king of herrings, a type of oarfish. Specimens of ocean sunfish have been observed up to 3.3 metres (11 ft) in length and weighing up to 2,303 kilograms (5,080 lb). Other very large bony fish include the Atlantic blue marlin, some specimens of which have been recorded as in excess of 820 kilograms (1,800 lb), the black marlin, some sturgeon species, the giant grouper and the goliath grouper, both which can exceed 400 kilograms (880 lb) in weight. In contrast, the dwarf pygmy goby measures a minute 15 millimetres (0.59 in).
Arapaima gigas is the largest species of freshwater bony fish. The largest bony fish ever was Leedsichthys, which dwarfed the beluga sturgeon, ocean sunfish, giant grouper, and all the other giant bony fishes alive today.