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A further subtype of T cells is called regulatory T cells T reg. Modern human vaccines contain adjuvants that are less prone to cause side effects. The patho-anatomic picture is not specific to these compounds. Breakdown of oral tolerance causes diseases like inflammatory bowel disease and celiac disease. The mouth may be modified into a suckermouth adapted for clinging onto objects in fast-moving water. The classical adjuvant for immunization of laboratory animals was complete Freund's adjuvant , consisting of inactivated Mycobacterium tuberculosis in mineral oil.
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Since it remains hard to accurately predict bioaccumulation in fish, even with highly sophisticated models, analyses of tissue levels are required. The most promising fish bioaccumulation markers are body burdens of persistent organic pollutants, like PCBs and DDTs. Since PCDD and PCDF levels in fish tissues are very low as compared with the sediment levels, their value as bioaccumulation markers remains questionable. Easily biodegradable compounds, such as PAHs and chlorinated phenols, do not tend to accumulate in fish tissues in quantities that reflect the exposure.
Semipermeable membrane devices SPMDs have been successfully used to mimic bioaccumulation of hydrophobic organic substances in aquatic organisms.
In order to assess exposure to or effects of environmental pollutants on aquatic ecosystems, the following suite of fish biomarkers may be examined: All fish biomarkers are evaluated for their potential use in ERA programs, based upon six criteria that have been proposed in the present paper.
People may be exposed to mercury in any of its forms under different circumstances. However, exposure mainly occurs through consumption of fish and shellfish contaminated with methylmercury and through worker inhalation of elemental mercury vapours during industrial processes. Cooking does not eliminate mercury. All humans are exposed to some level of mercury. Most people are exposed to low levels of mercury, often through chronic exposure continuous or intermittent long term contact.
However, some people are exposed to high levels of mercury, including acute exposure exposure occurring over a short period of time, often less than a day. An example of acute exposure would be mercury exposure due to an industrial accident. Generally, two groups are more sensitive to the effects of mercury.
Foetuses are most susceptible to developmental effects due to mercury. Methylmercury exposure in the womb can result from a mother's consumption of fish and shellfish. It can adversely affect a baby's growing brain and nervous system. The primary health effect of methylmercury is impaired neurological development. Therefore, cognitive thinking, memory, attention, language, and fine motor and visual spatial skills may be affected in children who were exposed to methylmercury as foetuses.
The second group is people who are regularly exposed chronic exposure to high levels of mercury such as populations that rely on subsistence fishing or people who are occupationally exposed. Among selected subsistence fishing populations, between 1. A significant example of mercury exposure affecting public health occurred in Minamata, Japan, between and , where a factory producing acetic acid discharged waste liquid into Minamata Bay.
The discharge included high concentrations of methylmercury. The bay was rich in fish and shellfish, providing the main livelihood for local residents and fishermen from other areas.
For many years, no one realised that the fish were contaminated with mercury, and that it was causing a strange disease in the local community and in other districts. At least 50 people were affected to some extent and more than cases of Minamata disease were certified. Minamata disease peaked in the s, with severe cases suffering brain damage, paralysis, incoherent speech and delirium.
Elemental and methylmercury are toxic to the central and peripheral nervous systems. The inhalation of mercury vapour can produce harmful effects on the nervous, digestive and immune systems, lungs and kidneys, and may be fatal. It is often absent in fast swimming fishes such as the tuna and mackerel families.
The condition of a bladder open to the esophagus is called physostome , the closed condition physoclist.
In the latter, the gas content of the bladder is controlled through a rete mirabilis , a network of blood vessels effecting gas exchange between the bladder and the blood. Fishes of the superorder Ostariophysi possess a structure called the Weberian apparatus , a modification which allow them to hear better.
This ability which may well explain the marked success of otophysian fishes. This allows the transmission of vibrations to the inner ear. A fully functioning Weberian apparatus consists of the swim bladder, the Weberian ossicles, a portion of the anterior vertebral column, and some muscles and ligaments. Fish reproductive organs include testes and ovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused.
The genital papilla is a small, fleshy tube behind the anus in some fishes, from which the sperm or eggs are released; the sex of a fish often can be determined by the shape of its papilla.
Most male fish have two testes of similar size. In the case of sharks , the testis on the right side is usually larger. The primitive jawless fish have only a single testis, located in the midline of the body, although even this forms from the fusion of paired structures in the embryo. Under a tough membranous shell, the tunica albuginea , the testis of some teleost fish, contains very fine coiled tubes called seminiferous tubules. The tubules are lined with a layer of cells germ cells that from puberty into old age, develop into sperm cells also known as spermatozoa or male gametes.
The developing sperm travel through the seminiferous tubules to the rete testis located in the mediastinum testis , to the efferent ducts , and then to the epididymis where newly created sperm cells mature see spermatogenesis. The sperm move into the vas deferens , and are eventually expelled through the urethra and out of the urethral orifice through muscular contractions. However, most fish do not possess seminiferous tubules.
Instead, the sperm are produced in spherical structures called sperm ampullae. These are seasonal structures, releasing their contents during the breeding season, and then being reabsorbed by the body. Before the next breeding season, new sperm ampullae begin to form and ripen. The ampullae are otherwise essentially identical to the seminiferous tubules in higher vertebrates, including the same range of cell types.
In terms of spermatogonia distribution, the structure of teleosts testes has two types: Fish can present cystic or semi-cystic spermatogenesis in relation to the release phase of germ cells in cysts to the seminiferous tubules lumen. Many of the features found in ovaries are common to all vertebrates, including the presence of follicular cells and tunica albuginea There may be hundreds or even millions of fertile eggs present in the ovary of a fish at any given time.
Fresh eggs may be developing from the germinal epithelium throughout life. Corpora lutea are found only in mammals, and in some elasmobranch fish; in other species, the remnants of the follicle are quickly resorbed by the ovary.
In some elasmobranchs , only the right ovary develops fully. In the primitive jawless fish , and some teleosts, there is only one ovary, formed by the fusion of the paired organs in the embryo. Fish ovaries may be of three types: In the first type, the oocytes are released directly into the coelomic cavity and then enter the ostium , then through the oviduct and are eliminated. Secondary gymnovarian ovaries shed ova into the coelom from which they go directly into the oviduct.
In the third type, the oocytes are conveyed to the exterior through the oviduct. Cystovaries characterize most teleosts, where the ovary lumen has continuity with the oviduct. Fish typically have quite small brains relative to body size compared with other vertebrates, typically one-fifteenth the brain mass of a similarly sized bird or mammal.
Fish brains are divided into several regions. At the front are the olfactory lobes , a pair of structures that receive and process signals from the nostrils via the two olfactory nerves.
The olfactory lobes are very large in fish that hunt primarily by smell, such as hagfish, sharks, and catfish. Behind the olfactory lobes is the two-lobed telencephalon , the structural equivalent to the cerebrum in higher vertebrates. In fish the telencephalon is concerned mostly with olfaction. The forebrain is connected to the midbrain via the diencephalon in the diagram, this structure is below the optic lobes and consequently not visible. The diencephalon performs functions associated with hormones and homeostasis.
This structure detects light, maintains circadian rhythms, and controls color changes. These are very large in species that hunt by sight, such as rainbow trout and cichlids. The hindbrain or metencephalon is particularly involved in swimming and balance. The brain stem or myelencephalon is the brain's posterior. Vertebrates are the only chordate group to exhibit a proper brain. A slight swelling of the anterior end of the dorsal nerve cord is found in the lancelet , though it lacks the eyes and other complex sense organs comparable to those of vertebrates.
Other chordates do not show any trends towards cephalisation. The front end of the nerve tube is expanded by a thickening of the walls and expansion of the central canal of spinal cord into three primary brain vesicles: The prosencephalon forebrain , mesencephalon midbrain and rhombencephalon hindbrain , further differentiated in the various vertebrate groups. Vesicles of the forebrain are usually paired, giving rise to hemispheres like the cerebral hemispheres in mammals.
The circuits in the cerebellum are similar across all classes of vertebrates , including fish, reptiles, birds, and mammals. There is considerable variation in the size and shape of the cerebellum in different vertebrate species. In amphibians , lampreys , and hagfish , the cerebellum is little developed; in the latter two groups, it is barely distinguishable from the brain-stem.
Although the spinocerebellum is present in these groups, the primary structures are small paired nuclei corresponding to the vestibulocerebellum. The cerebellum of cartilaginous and bony fishes is extraordinarily large and complex. In at least one important respect, it differs in internal structure from the mammalian cerebellum: The fish cerebellum does not contain discrete deep cerebellar nuclei.
Instead, the primary targets of Purkinje cells are a distinct type of cell distributed across the cerebellar cortex, a type not seen in mammals. In mormyrid fish a family of weakly electrosensitive freshwater fish , the cerebellum is considerably larger than the rest of the brain put together.
The largest part of it is a special structure called the valvula , which has an unusually regular architecture and receives much of its input from the electrosensory system. Most species of fish and amphibians possess a lateral line system that senses pressure waves in water.
One of the brain areas that receives primary input from the lateral line organ, the medial octavolateral nucleus, has a cerebellum-like structure, with granule cells and parallel fibers. In electrosensitive fish, the input from the electrosensory system goes to the dorsal octavolateral nucleus, which also has a cerebellum-like structure. In ray-finned fishes by far the largest group , the optic tectum has a layer — the marginal layer — that is cerebellum-like.
A neuron is called identified if it has properties that distinguish it from every other neuron in the same animal—properties such as location, neurotransmitter, gene expression pattern, and connectivity—and if every individual organism belonging to the same species has one and only one neuron with the same set of properties.
In vertebrates, the best known identified neurons are the gigantic Mauthner cells of fish. Each Mauthner cell has an axon that crosses over, innervating neurons at the same brain level and then travelling down through the spinal cord, making numerous connections as it goes. The synapses generated by a Mauthner cell are so powerful that a single action potential gives rise to a major behavioral response: Functionally this is a fast escape response , triggered most easily by a strong sound wave or pressure wave impinging on the lateral line organ of the fish.
Mauthner cells are not the only identified neurons in fish—there are about 20 more types, including pairs of "Mauthner cell analogs" in each spinal segmental nucleus. Although a Mauthner cell is capable of bringing about an escape response all by itself, in the context of ordinary behavior other types of cells usually contribute to shaping the amplitude and direction of the response. Mauthner cells have been described as command neurons. A command neuron is a special type of identified neuron, defined as a neuron that is capable of driving a specific behavior all by itself.
The concept of a command neuron has, however, become controversial, because of studies showing that some neurons that initially appeared to fit the description were really only capable of evoking a response in a limited set of circumstances. Immune organs vary by type of fish. These fish rely on regions of lymphoid tissue within other organs to produce immune cells. For example, erythrocytes , macrophages and plasma cells are produced in the anterior kidney or pronephros and some areas of the gut where granulocytes mature.
They resemble primitive bone marrow in hagfish. Cartilaginous fish sharks and rays have a more advanced immune system. They have three specialized organs that are unique to chondrichthyes ; the epigonal organs lymphoid tissue similar to mammalian bone that surround the gonads, the Leydig's organ within the walls of their esophagus, and a spiral valve in their intestine.
These organs house typical immune cells granulocytes, lymphocytes and plasma cells. They also possess an identifiable thymus and a well-developed spleen their most important immune organ where various lymphocytes , plasma cells and macrophages develop and are stored.
Chondrostean fish sturgeons, paddlefish and bichirs possess a major site for the production of granulocytes within a mass that is associated with the meninges membranes surrounding the central nervous system. Their heart is frequently covered with tissue that contains lymphocytes, reticular cells and a small number of macrophages.
The chondrostean kidney is an important hemopoietic organ; where erythrocytes, granulocytes, lymphocytes and macrophages develop. Like chondrostean fish, the major immune tissues of bony fish or teleostei include the kidney especially the anterior kidney , which houses many different immune cells.
Much like the mammalian immune system, teleost erythrocytes, neutrophils and granulocytes are believed to reside in the spleen whereas lymphocytes are the major cell type found in the thymus.
Although not confirmed as yet, this system presumably will be where naive unstimulated T cells accumulate while waiting to encounter an antigen. From Wikipedia, the free encyclopedia. External anatomy of a bony fish Hector's lanternfish 1. Internal anatomy of a bony fish.
Anatomical directions and axes. The X-ray tetra Pristella maxillaris has a visible backbone. The spinal cord is housed within its backbone. A vertebra diameter 5 mm of a small ray-finned fish. Skull of a northern pike. Zenion hololepis is a small deep water fish with large eyes. The deep sea half-naked hatchetfish has eyes which look overhead where it can see the silhouettes of prey.
Cycloid scales covering rohu. Types of caudal tail fin:. Internal organs of a female Atlantic cod 1. Gas bladder , 3. Pyloric caeca , 5. Blood flow through the heart: Cardiovascular cycle in a fish. The swim bladder of a rudd. Reproductive processes in fish. Fish diseases and parasites.
Archived from the original on 28 April Retrieved 27 June Modern Text Book of Zoology: Archived from the original on Retrieved 15 July Retrieved 13 July Functional anatomy of the vertebrates: Journal of Molecular Evolution.
Retrieved 22 November Biology , Seventh Edition. Benjamin Cummings, San Francisco, California. Biology, Evolution, and Ecology pp. Nutrition and Feeding of Fish and Crustaceans. Instant Notes Animal Biology. Encyclopedia of Fish Physiology: