In the Book of Jonah, a work of Jewish literature probably written in the fourth century BC, the central figure, a prophet named Jonah, is swallowed by a giant fish after being thrown overboard by the crew of the ship he is travelling on. [112] [113] [114] The fish later vomits Jonah out on shore after three days. [112] [113] [114] This book was later included as part of the Hebrew Bible, or Christian Old Testament, [115] [116] and a version of the story it contains is summarized in Surah 37:139-148 of the Quran. [117] Early Christians used the ichthys, a symbol of a fish, to represent Jesus, [110] [111] because the Greek word for fish, ΙΧΘΥΣ Ichthys, could be used as an acronym for "Ίησοῦς Χριστός, Θεοῦ Υἱός, Σωτήρ" (Iesous Christos, Theou Huios, Soter), meaning "Jesus Christ, Son of God, Saviour". [110] [111] The gospels also refer to "fishers of men" [118] and feeding the multitude. In the dhamma of Buddhism, the fish symbolize happiness as they have complete freedom of movement in the water. J. Mallatt, J. Sullivan (1998) 28S and 18S rDNA sequences support the monophyly of lampreys and hagfishes Molecular Biology and Evolution V 15, Issue 12, pp. 1706–1718 EU fish quota deal hammered out". BBC News. 21 December 2006. Archived from the original on 26 December 2006 . Retrieved 18 January 2006. In bony fish, most fins may have spines or rays. A fin may contain only spiny rays, only soft rays, or a combination of both. If both are present, the spiny rays are always anterior. Spines are generally stiff, sharp and unsegmented. Rays are generally soft, flexible, segmented, and may be branched. This segmentation of rays is the main difference that distinguishes them from spines; spines may be flexible in certain species, but never segmented. UK 'must shield fishing industry' ". BBC News. 3 November 2006. Archived from the original on 30 November 2006 . Retrieved 18 January 2006.

The word for fish in English and the other Germanic languages ( German Fisch; Gothic fisks) is inherited from Proto-Germanic, and is related to the Latin piscis and Old Irish īasc, though the exact root is unknown; some authorities reconstruct a Proto-Indo-European root * peysk-, attested only in Italic, Celtic, and Germanic. [8] [9] [10] [11] Immune organs vary by type of fish. [70] In the jawless fish (lampreys and hagfish), true lymphoid organs are absent. 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. Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another. The production of sounds as a means of communication among fish is most often used in the context of feeding, aggression or courtship behaviour. [3] The sounds emitted can vary depending on the species and stimulus involved. Fish can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder. [66] Stridulatory French grunts – Haemulon flavolineatumWinfred Philipp Lehmann, Helen-Jo J. Hewitt, Sigmund Feist, A Gothic etymological dictionary, 1986, s.v. fisks p. 118 Like the Nile tilapia, the kidney of some fish shows its three parts; head, trunk, and tail kidneys. [35] Rose, J.D. 2003. A Critique of the paper: "Do fish have nociceptors: Evidence for the evolution of a vertebrate sensory system" " (PDF). Archived from the original (PDF) on 8 June 2011 . Retrieved 21 May 2011.

Band, Arnold J. (2003). Studies in Modern Jewish Literature. JPS Scholar of Distinction Series. Philadelphia, Pennsylvania: The Jewish Publication Society. pp.106–107. ISBN 978-0-8276-0762-0. Archived from the original on 17 March 2023 . Retrieved 12 December 2020. Among the deities said to take the form of a fish are Ika-Roa of the Polynesians, Dagon of various ancient Semitic peoples, the shark-gods of Hawaiʻi and Matsya of the Hindus. The astrological symbol Pisces is based on a constellation of the same name, but there is also a second fish constellation in the night sky, Piscis Austrinus. [119] Moyle, Peter B.; Cech, Joseph J. (2003). Fishes, An Introduction to Ichthyology (5thed.). Benjamin Cummings. ISBN 978-0-13-100847-2. Juvenile bichirs have external gills, a very primitive feature that they share with larval amphibians.

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a b Jurd, Richard David (January 2004). Instant Notes Animal Biology. Garland Science. p.134. ISBN 978-1-85996-325-8. Archived from the original on 6 December 2016 . Retrieved 13 March 2016.

a b c Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp.353–354. ISBN 978-0-03-910284-5. The heart has two chambers and pumps the blood through the respiratory surfaces of the gills and then around the body in a single circulatory loop. [3] The eyes are adapted for seeing underwater and have only local vision. [ definition needed] There is an inner ear but no external or middle ear. Low-frequency vibrations are detected by the lateral line system of sense organs that run along the length of the sides of fish, which responds to nearby movements and to changes in water pressure. [2] The strict biological definition of a fish, above, is sometimes called a true fish. True fish are also referred to as finfish or fin fish to distinguish them from other aquatic life harvested in fisheries or aquaculture. Chilmonczyk, S. (1992). " The thymus in fish: development and possible function in the immune response". Annual Review of Fish Diseases. 2: 181–200. doi: 10.1016/0959-8030(92)90063-4. a b Gaines, Janet Howe (2003). Forgiveness in a Wounded World: Jonah's Dilemma. Atlanta, Georgia: Society of Biblical Literature. pp.8–9. ISBN 978-1-58983-077-6. Archived from the original on 17 March 2023 . Retrieved 12 December 2020.Fins are the most distinctive features of fish. They are either composed of bony spines or rays protruding from the body with skin covering them and joining them together, either in a webbed fashion as seen in most bony fish, or similar to a flipper as seen in sharks. Apart from the tail or caudal fin, fins have no direct connection with the spine and are supported by muscles only. Their principal function is to help the fish swim. Fins can also be used for gliding or crawling, as seen in the flying fish and frogfish. Fins located in different places on the fish serve different purposes, such as moving forward, turning, and keeping an upright position. For every fin, there are a number of fish species in which this particular fin has been lost during evolution. [ citation needed] Spines and rays [ edit ] Owen, Richard (1843). Lectures on the comparative anatomy and physiology of the invertebrate animals. London: Longman, Brown, Green, and Longmans. pp.283–284. Fish from multiple groups can live out of the water for extended periods. Amphibious fish such as the mudskipper can live and move about on land for up to several days, [ dubious – discuss] or live in stagnant or otherwise oxygen-depleted water. Many such fish can breathe air via a variety of mechanisms. The skin of anguillid eels may absorb oxygen directly. The buccal cavity of the electric eel may breathe air. Catfish of the families Loricariidae, Callichthyidae, and Scoloplacidae absorb air through their digestive tracts. [39] Lungfish, with the exception of the Australian lungfish, and bichirs have paired lungs similar to those of tetrapods and must surface to gulp fresh air through the mouth and pass spent air out through the gills. Gar and bowfin have a vascularized swim bladder that functions in the same way. Loaches, trahiras, and many catfish breathe by passing air through the gut. Mudskippers breathe by absorbing oxygen across the skin (similar to frogs). A number of fish have evolved so-called accessory breathing organs that extract oxygen from the air. Labyrinth fish (such as gouramis and bettas) have a labyrinth organ above the gills that performs this function. A few other fish have structures resembling labyrinth organs in form and function, most notably snakeheads, pikeheads, and the Clariidae catfish family. Tetrapods ( amphibians, reptiles, birds and mammals) emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish ( pisces or ichthyes) are rendered paraphyletic by excluding the tetrapods, and are therefore not considered a formal taxonomic grouping in systematic biology, unless it is used in the cladistic sense, including tetrapods, [6] [7] although usually " vertebrate" is preferred and used for this purpose (fish plus tetrapods) instead. Furthermore, cetaceans, although mammals, have often been considered fish by various cultures and time periods. A neuron is "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. [65] In vertebrate nervous systems, very few neurons are "identified" in this sense (in humans, there are believed to be none). In simpler nervous systems, some or all neurons may be thus unique. [66]