Chondrichthyes Sensory Systems. Reviews in Fish Biology and Fisheries, 20(4), 571590. Osteichthyes are highly diverse and come in a number of shapes and sizes. The old placoderms did not have teeth at all, but had sharp bony plates in their mouth. (1983). 1. Die Parietalorgane. Theme by Anders Norn. ), Biology of sharks and their relatives II (pp. Their inner ears consist of 3 large semicircular canals which aid in balance and orientation. After emerging from its capsule, the embryo remains in the oviduct of the mother, nourished by the yolk sac to which it remains attached. The lateral line system of nerves provides osteichthyes with a sense of hearing, in the form of vibrations in the water, which can help osteichthyes avoid predators and detect prey. An egg of the whale shark found in the Gulf of Mexico measured 30 cm (12 inches) long by about 14 cm (5.5 inches) wide and was 8 cm (3 inches) thick. This is a preview of subscription content, access via your institution. The first abundant genus of shark, Cladoselache, appeared in the oceans during the Devonian Period. Only their teeth, and sometimes their vertebrae, have calcium in them! These are the telencephalon, diencephalon, mesencephalon, and the hind brain. Google Scholar. Some nerves come directly from the brain and are responsible for picking up important sensory information such as taste, smell, and sight. Skates, which sometimes hold the lower surface of the head slightly above the bottom, may inhale some water through the mouth; mantas, which have small spiracles and live near the surface, respire chiefly through the mouth. Eye growth in sharks: Ecological implications for changes in retinal topography and visual resolution. Outline the development of jaws in vertebrates. The class Chondrichthyes is divided into two subclasses: the Elasmobranchii (sharks, skates, and rays) and the Holocephali (elephant sharks and chimaeras). However, preliminary studies believe the parasite can act as a lure for prey giving the shark a a benefit as well. A distinct heart, anteroventral to the liver, is enclosed in a pericardial sac. These scales make their skin so rough it can be used as sand paper! Journal of Experimental Biology, 207(20), 34633476. Lowenstein, O., & Roberts, T. D. M. (1951). The eggs are enveloped in a horny shell, usually equipped with tendrils for coiling around solid objects or with spikelike projections for anchoring in mud or sand. Class Agnatha - Angelena Mangieri Several shark species are viviparousthat is, the yolk sac develops folds and projections that interdigitate with corresponding folds of the uterine wall, thus forming a yolk-sac placenta through which nutrient material is passed from the mother. Schluessel, V., Bennett, M. B., Bleckmann, H., Blomberg, S., & Collin, S. P. (2008). In general, pelagic species must keep swimming to keep oxygenated water moving through their gills, whilst demersal species can actively pump water in through their spiracles and out through their gills. Besides the elongated upper lobe, the tail consists of two shorter lobes. https://doi.org/10.1002/jmor.1068. Sensory adaptations to the environment: Electroreceptors as a case study. Its like a teacher waved a magic wand and did the work for me. Litherland, L., Collin, S. P., & Fritsches, K. A. Reproduction and Development in Chondrichthyan Fishes The water reaches the mouth primarily through grooves leading there from the nostrils. Acta Zool 90:134-151. (Campagno et al. We typically think of oviparousity as the most primitive and viviparousity as more advanced. https://doi.org/10.1206/3875.1. The word Holocephali means complete head. In chondrichthyans, the nervous system is composed of a small brain, 8-10 pairs of cranial nerves, and a spinal chord with spinal nerves. https://doi.org/10.1111/jfb.14068. Morphology of the mechanosensory lateral line system in elasmobranch fishes: Ecological and behavioral considerations. What are the Economic Benefits of Chondrichthyes? Explain how a shark is able to maintain buoyancy. They also eat plankton and other small organisms. In chondrichthyans, the nervous system is composed of a small brain, 8-10 pairs of cranial nerves, and a spinal chord with spinal nerves. CrossRef (2009). https://doi.org/10.1007/s11160-010-9162-x. At the rostral, or nose, end of the fish lie olfactory lobes, which provide the sense of smell. (2009). Correspondence to Fertilization is internal. The skeleton is cartilaginous. Chondrichthyes' sensory systems are part of the nervous system responsible for receiving external and internal stimuli and translating them into nerve impulses that are transmitted to the central nervous system where they are processed. Chondrichthyes Sensory Systems | SpringerLink Head morphology and pore distribution of carcharhinid and sphyrnid sharks. https://doi.org/10.1002/jmor.1068. https://doi.org/10.1111/jfb.14068. The Respiratory System Part 1: Structures and Mechanisms of Breathing; The Respiratory System Part 2: Regulation of Breathing . Chondrichthyes is subdivided into two subclasses: Elasmobranchii- Sharks and rays, skates, sawfishes. With the mouth closed, they contract the bucco-pharyngeal cavity while dilating the gill pouches, thus drawing the water over the gills where the exchange of oxygen and carbon dioxide takes place. In A. Oppel (Ed. (2010). https://doi.org/10.1023/A:1007647924559. Chondrichthyans have tooth-like scales called dermal denticles or placoid scales. Alternative life-history styles of cartilaginous fishes in time and space. There are so many misconceptions about this class of vertebrates; education is the first step to protecting sharks which in turn will help protect food webs and biodiversity in our oceans. Department of Psychology, Oakland University Department of Psychology, Rochester, MI, USA, Missouri Southern State University, Joplin, MO, USA, Slobodian, V., Citeli, N., Cesar, S.E., Soares, K.D.A. The Chondrichthyes are the cartilaginous fishes, such as sharks and rays, while the Osteichthyes are the bony fishes. 1254). 6. She is a current PhD student in biology at Wake Forest University, and has been teaching undergraduate students biology for the last three years. However, Chondrichthyans also have special sensing organs called the Ampullae of Lorenzini giving them a seventh sense., Figure 4: Close up of a shark rostum notice the series of dots scatter throughout. Meredith, T. L., & Kajiura, S. M. (2010). The O diffuses into the gills as water passes over them on their way out of the organism's body. In Greek, elasmo means Plate and branchia means gill, hence we can tell that long and broad flattened gills are the characteristics of these fishes. Newton, K. C., Gill, A. Google Scholar. As the density of the cartilage is less as compared to the bones it provides more flexibility and hence they can bend easily as compared to the bony fishes. Class Chondrichthyes - The Tree of Life Cartilaginous Fish - an overview | ScienceDirect Topics The central nervous system of osteichthyes is comprised of a brain and a spinal cord, just like our own central nervous system.Most fish brains are very small compared to overall body size, about 1/15th the mass of a similarly-sized mammal or bird.Other bony fish, such as the freshwater elephant fish (Family Mormyridae), have exceptionally large Didier, D. A. Intestines are short, but have folds arranged in a spiral (increasing surface area). Environmental Biology of Fishes, 61(2), 125133. In J. C. Carrier, J. A DiI-tracing study of the neural connections of the pineal organ in two elasmobranchs (Scyliorhinus canicula and Raja montagui) suggests a pineal projection to the midbrain GnRH-immunoreactive nucleus. Meredith, T. L., Kajiura, S. M., & Hansen, A. Understand bony fish nervous systems and see a labeled diagram of a fish brain. This orients them and helps with migration. Many larger, pelagic species, such as the mackerel sharks (Lamnidae) and the thresher sharks (Alopiidae), no longer possess them. In A. Oppel (Ed. The Greek root 'ostei-' means 'bone'. With the exception of some who are able to breathe . Electroreception. Journal of Morphology, 274, 447455. In many fish, the cerebellum is the largest part of the brain. In addition to eating other fish, molluscs, and crustaceans, predatory fishes also feed on other species of fish. A., Casper, B. M., Mann, D. A., & Demski, L. S. (2012). A., Castell, M. E., Aguilera, P. A., Pereira, C., Nogueira, J., Rodrguez-Cattaneo, A., & Lezcano, C. (2008). Brain and nervous system | Functional Morphology of the Brains of Crampton, W. G. R. (2019). The male grasps one of the females pectoral fins with his teeth to hold her in position as he inserts a clasper through a cavity (cloaca) and into a tube (oviduct). Agnatha also have a peripheral nervous system which includes cranial nerves and spinal nerves. Caputi, . Sensory biology of elasmobranchs. Signals obtained from sensory nerves are brought to the central nervous system for interpretation. CrossRef Jena: Bd V. Fisher. In J. Most species have large well-developed eyes. These select Elasmobranchii have the ability to withstand both salt and fresh water. https://doi.org/10.1007/978-3-319-55065-7_1018, DOI: https://doi.org/10.1007/978-3-319-55065-7_1018, eBook Packages: Behavioral Science and PsychologyReference Module Humanities and Social Sciences. https://doi.org/10.1007/BF00206272. Nutrition is crucial to children's physical and mental development. https://doi.org/10.1242/jeb.01140. Integrative Zoology, 4(1), 312. B., & Kajiura, S. M. (2019). Environmental Biology of Fishes, 61(2), 125133. Apart from electric rays, which have a thick and flabby body, with soft, loose skin, chondrichthyans have tough skin covered with dermal teeth (again, Holocephali is an exception, as the teeth are lost in adults, only kept on the clasping organ seen on the caudal ventral surface of the male), also called placoid scales (or dermal denticles), making it feel like sandpaper. The Journal of Physiology. Environmental Biology of Fishes, 60(13), 4775. Morphometric and ultrastructural comparison of the olfactory system in elasmobranchs: The significance of structurefunction relationships based on phylogeny and ecology. A distinct heterocercal tail protrudes from the lower lobe as well as the extension of vertebrae into the upper lobe. Chicago: SEM. Hammerhead sharks are one such migratory shark. Cartilage is the flexible substance found that gives human noses and ears their shape! (1983). Cell and Tissue Research, 303(3), 391401. Schluessel, V., Bennett, M. B., Bleckmann, H., Blomberg, S., & Collin, S. P. (2008). As poikilothermic animals, they cannot regulate their internal body temperature. Kajiura, S. M. (2001). Crampton, W. G. R. (2019). Some fishes also have specific organs that can omit electric signals, such as those found in electric eels or knife fishes. The mesencephalon is also often referred to as the mid brain. Examples of Chondrichthyes include sharks, skates, and chimeras. Most fish brains are very small compared to overall body size, about 1/15th the mass of a similarly-sized mammal or bird. Capture-induced premature birth and abortion (collectively called capture-induced parturition) occurs frequently in sharks/rays when fished. Five to seven pairs of gills are present excluding the operculum. 1254). Lowenstein, O., & Roberts, T. D. M. (1951). The neuroecology of cartilaginous fishes: sensory strategies for In addition to sharks and rays, nearly everything that swims is prey for both animals. Visual Neuroscience, 26(4), 397. https://doi.org/10.1017/S0952523809990150. Denticles usually provide protection, and in most cases, streamlining. Christina graduated with a Master's in biology from the University of Louisiana at Lafayette. Environmental Biology of Fishes, 28(14), 3375. Carrier, J. Musick, & M. Heithaus (Eds. Maruska, K. P., & Tricas, T. C. (2004). However, many of their life history traits, such as low fecundity, the production of small numbers of highly precocious young, slow growth rates, and late maturity, make them highly . (PDF) Chondrichthyes Sensory Systems - ResearchGate Litherland, L., Collin, S. P., & Fritsches, K. A. In A. Oppel (Ed. Chondrichthyes sensory systems are part of the nervous system responsible for receiving external and internal stimuli and translating them into nerve impulses that are transmitted to the central nervous system where they are processed. Fish is not just crucial to the ecosystem but is also very important to us as it provides the body with many nutrients and micronutrients. Part of Springer Nature. Yopak, K. E., Lisney, T. J., & Collin, S. P. (2015). Maisey, J. G., Miller, R., Pradel, A., Denton, J. S., Bronson, A., & Janvier, P. (2017). Journal of Experimental Biology, 207(20), 34633476. Electroreceptors are a sensory organ that can detect electric signals. praeside Arvid. Electroreception, electrogenesis and electric signal evolution. Chondrichthyes Nervous system. Kempster, R. M., McCarthy, I. D., & Collin, S. P. (2012). In the majority of ovoviviparous sharks and rays, organically rich uterine secretions provide supplemental nourishment, which is absorbed by the yolk sac and in many cases by appendages borne on its stalk. At the head, they have 2 eyes that sense light and do eye stuff. https://doi.org/10.1023/A:1007647924559. Electroreception in marine fishes: Chondrichthyans. Gardiner, J. M., Hueter, R. E., Maruska, K. P., Sisneros, J. Some fishes have specialized nervous systems that stimulate organs capable of generating electric fields. Fun fact: Sharks can use their ampullae to navigate the globe by tracking earths electromagnetic field. We have grown leaps and bounds to be the best Online Tuition Website in India with immensely talented Vedantu Master Teachers, from the most reputed institutions. Sensory adaptations to the environment: Electroreceptors as a case study. Part of Springer Nature. https://doi.org/10.1113/jphysiol.1951.sp004638. Test of the mechanotactile hypothesis: Neuromast morphology and response dynamics of mechanosensory lateral line primary afferents in the stingray. Producing an electric signal is a specialization in the nervous system of some Osteichthyes. The mid brain plays an important role in deciphering visual information. This means that fish are capable of feeling stimuli related to pain. Reviews in Fish Biology and Fisheries, 20(4), 571590. Journal of Physiology-Paris, 102(46), 256271. Not all sharks are swimming noses: Variation in olfactory bulb size in cartilaginous fishes. Laboratrio de Ictiologia Sistemtica, Departamento de Zoologia, Instituto de Cincias Biolgicas, Campus Universitrio Darcy Ribeiro, Universidade de Braslia, Braslia, DF, Brazil, Laboratrio de Fauna e Unidades de Conservao, Departamento de Engenharia Florestal, Faculdade de Tecnologia, Universidade de Braslia, Braslia, DF, Brazil, Laboratrio de Anatomia Comparada de Vertebrados, Departamento de Cincias Fisiolgicas, Instituto de Cincias Biolgicas, Universidade de Braslia, Braslia, Brazil, Laboratory of Vertebrate Comparative Anatomy, Department of Zoology, University of Braslia, Braslia, Brazil, Laboratory of Ichthyology, Department of Zoology, University of So Paulo, So Paulo, Brazil, You can also search for this author in (1995). Maisey, J. G., Miller, R., Pradel, A., Denton, J. S., Bronson, A., & Janvier, P. (2017). For instance, the human brain is a complex organ with multiple parts and components. Grogan E, Lund R (2009) Two new iniopterygians (Chondrichthyes) from the Mississippian (Serpukhovian) Bear Gulch Limestone of Montana with evidence of a new form of chondrichthyan neurocranium. Kempster, R. M., McCarthy, I. D., & Collin, S. P. (2012). (2022). https://doi.org/10.1111/j.1749-4877.2008.00130.x. CrossRef Google Scholar Gruber SH (1977) The visual system of sharks; adaptations and capability. Veronica Slobodian . That electrical signal goes through fluid filled pores and strike nerves to signal the brain. Gardiner, J. M., Hueter, R. E., Maruska, K. P., Sisneros, J. Journal of Morphology, 274, 447455. ), Lehrbuch der vergleichenden mikroskopischen Anatomie der Wirbeltiere (pp. https://doi.org/10.1111/j.1749-4877.2008.00130.x. Vision in sharks and rays: Opsin diversity and colour vision. Yopak, K. E., Lisney, T. J., & Collin, S. P. (2015). The somatotopic organization of the olfactory bulb in elasmobranchs. Integrative Zoology, 4(1), 312. Alternative life-history styles of cartilaginous fishes in time and space. https://doi.org/10.1002/jmor.10661. The digestive system is well-developed. Behind the olfactory lobes sits the telencephalon, which is equivalent to the cerebrum in most other vertebrates. Some of the sharks, probably all the skates, possibly some of the guitarfishes, and all of the chimaeras are oviparous (egg-laying species). flashcard set. Nervous System- they have 5 parts brain which includes the highly developed olfactory region. https://doi.org/10.1111/jfb.13922. Lowenstein, O., & Roberts, T. D. M. (1951). Encyclopedia of Animal Cognition and Behavior pp 111Cite as. It contains lymphoid and hemopoietic tissue. In O. M. Johari (Ed. Class Chondrichthyes - Cartilaginous Fish - Untamed Science Remarks on the inner ear of elasmobranchs and its interpretation from skeletal labyrinth morphology. https://doi.org/10.1242/jeb.045849. In chondrichthyans, the nervous system is composed of a small brain, 8-10 pairs of cranial nerves, and a spinal chord with spinal nerves. As with all fish, sharks/relatives have a lateral line, which gives them a sixth sense to detect vibrations in water. The Wolffian ducts in males and Mullerian ducts in females become the functional urogenital ducts. (Homologous . Chondrichthyes: (Cartilaginous Fish-Sharks, Rays, and Skates The lateral line appears as a line that runs down the length of the body. The electric organs (which are often found within the tail) generate specific waveforms and amplitudes that are controlled by the nervous system. Do fishes have a nervous system? However, there is currently no evidence of this. Mandado, M., Molist, P., Anadon, R., & Yanez, J. PDF Chondrichthyes Sensory Systems - ResearchGate Chondrichthyes possess 5-7 pairs of gill slits. Their nervous system adaptations range from the wild and electric, to the generalized lateral line system that helps their entire body function like an ear. This also helps the animals to prey on one another. Extant chondrichthyes range in size from the 10 cm (3.9 in) finless sleeper ray to the 10 m (32 ft) whale shark. Brown, B. R. (2003). Four pairs of gills are present including the operculum. In J. C. Carrier, J. It also contains the cerebrum, which plays an important role in olfactory processes. As they do not have bone marrow, red blood cells are produced in the spleen and special tissue around the gonads. The Lateral line system has modified epithelial cells located externally which sense motion, vibration, and pressure in the water around them. Caputi, . 31 chapters | I feel like its a lifeline. Let's delve into the structure and function of the central nervous system in bony fish - the brain and spinal cord - as well as the peripheral nervous system - branching nerves that extend throughout the body. The males of European thornback rays ( Raja clavata) are about 50 cm (20 inches) wide when they reach first maturity, about seven years after birth; females are 60 to 70 cm (24 . Journal of Morphology, 274, 447455. Nature, 421(6922), 495495. 2, pp. Jena: Bd V. Fisher. Vertebrates are the largest group of chordates, with more than 62,000 living species. In the same way, visceral sensory and visceral motor neurons connect to the various viscera, or organs, of the fish. 2, pp. In O. M. Johari (Ed. The Greenland shark (Somniosus microcephalus), which attains 6.5 metres (21 feet) or more (although rarely taken larger than about 4 metres [13 feet]), grows only about 7.5 mm (about 0.3 inch) per year. Journal of Fish Biology, 95(1), 135154. Journal of Fish Biology, 95(1), 135154. Hart, N. S. (2020). In osteichthyes fish the cerebellum has a similar function, coordinating balance and controlling the movements that help fish swim. The cerebellum helps fishes maintain equilibrium, while the brain stem connects the spinal cord to the brain and coordinates sensory information. Do Cartilaginous Fishes Differ from Bony Fishes in Any Way? Boca Raton: CRC Press. Boca Raton: CRC Press. By the start of the Early Devonian, 419 million years ago, jawed fishes had divided into three distinct groups: the now extinct placoderms (a paraphyletic assemblage of ancient armoured fishes), the bony fishes, and the clade that includes spiny sharks and early cartilaginous fish. Phylogenetic and ecological factors influencing the number and distribution of electroreceptors in elasmobranchs. In Seminars in Cell & Developmental Biology. This is most likely a secondary evolved characteristic, which means there is not necessarily a connection between the teeth and the original dermal scales. Skates: Little skate, Small deep-water skate, Andaman leg skate, etc. Academic Press. Skates, stingrays, guitarfishes, and angel sharks frequently reverse the direction of flow through the spiracles, apparently to clear them of foreign matter. Ampullae of Lorenzini are a network of small jelly filled pores called electroreceptors which help the fish sense electric fields in water. Chondrichthyans have a closed circulatory system. Fishes also have somatic sensory nerves, which are nerves that are responsive to stimuli from muscles or the skin. Journal of Fish Biology, 95(1), 92134. Cell and Tissue Research, 303(3), 391401. Newton, K. C., Gill, A. Compagno, L. J. Chondrichthyes digestive system: The stomach, pharynx, mouth, intestines, and cloaca make up the digestive system. Many believe the jaw developed first as a way to increase respiratory efficiency eating was a secondary function! Nerves run throughout the body and communicate with a number of structures. They have several sensory organs which provide information to be processed. A., & Demski, L. S. (2004). Meredith, T. L., Kajiura, S. M., & Hansen, A. Originally, the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. According to the structure of the endoskeleton, Pisces has two types of classes: the Chondrichthyes and the Osteichthyes. The Chondrichthyes are the basalmost extant branch of Gnathostomata and comprehend a monophyletic group of fishes with fossils and extant representatives distributed in 65 families with 1282 valid species. Growth of a few shark species has been measured or estimated by the differences in length at the times of tagging and recapturing specimens. https://doi.org/10.1007/978-3-319-47829-6_1018-2, DOI: https://doi.org/10.1007/978-3-319-47829-6_1018-2, eBook Packages: Springer Reference Behavioral Science and PsychologyReference Module Humanities and Social Sciences, DOI: https://doi.org/10.1007/978-3-319-47829-6_1018-1, Over 10 million scientific documents at your fingertips, Not logged in Nutrients supplied by blood vessels. A DiI-tracing study of the neural connections of the pineal organ in two elasmobranchs (Scyliorhinus canicula and Raja montagui) suggests a pineal projection to the midbrain GnRH-immunoreactive nucleus. https://doi.org/10.1007/s00429-014-0705-0. They collect water in the mouths which is then passed through the gills. - 177.10.89.34. Kempster, R. M., McCarthy, I. D., & Collin, S. P. (2012). A. Musick, & M. R. Heithaus (Eds. Caputi, . Hart, N. S. (2020). Journal of Fish Biology, 80(5), 20552088. Which one is exclusive to this class? Fishes in the class Chondrichthyes are included in the division Gnathostomata since they have jaws. Environmental Biology of Fishes, 61(2), 125133. A fish's brain is broken up into the telencephalon (which contains the cerebrum and olfactory lobes), diencephalon (which contains structures such as the pineal body, pituitary gland, thalamus, hypothalamus, and saccus vasculosus), mesencephalon (which contains the various white and gray zones), and hind brain (composed of the cerebellum and brain stem). [17][18] Shenacanthus vermiformis, which lived 436 million years ago, had thoracic armour plates resembling those of placoderms.[19]. Behavior and physiology of mechanoreception: Separating signal and noise. The localization and analysis of the responses to vibration from the isolated elasmobranch labyrinth: A contribution to the problem of the evolution of hearing in vertebrates. Osteichthyes are bony fishes with ossified skeletons, while Chondrichthyes are those with skeletons composed largely of cartilage. A. Musick, & M. R. Heithaus (Eds. The nervous system in fishes can be divided into two parts: the central nervous system and the peripheral nervous system. https://doi.org/10.1007/BF00206272. (2013). The nervous system is composed of neural tissue which works by reacting to stimuli and sending responses via electric signals. Holocephali- Chimaeras, also known as ghost sharks. The fish brain is generally divided into four different components. With this, fishes can detect when the water around them moves, alerting them of a passing nearby fish. Then, with the mouth still closed, they contract the bucco-pharyngeal cavity and gill pouches, and the gill slits are opened to expel the water. Unit 2-3: Mechanisms of Evolution and Natural Selection, Unit 3a-1: Genetic Modification and Gene Transfer, Unit 5-3: Phylum Platyhelminthes Webquest Notes, Unit 5-4: Phylum Nematoda Webquest Notes. Each gill has between five and seven blades. - 167.172.102.133. The Journal of Physiology. CrossRef A review of the sensory biology of chimaeroid fishes (Chondrichthyes; Holocephali). https://doi.org/10.1002/jmor.10661. A fish's spinal cord transmits motor messages to its peripheral nerves, and sends sensory messages back to the brain. Compagno, L. J. Journal of Morphology, 269(11), 13651386. Fish contain pain receptors called nociceptors like humans do. The ampullae are concentrated on the head, particularly . Kardong, K. (2016). The nervous system is composed of the nerves, spinal cord, and brain. 8. https://doi.org/10.1111/j.1749-4877.2008.00130.x. It includes sharks and rays, skates, and sawfishes. They differ from Chondrichthyes, which have a skeleton composed largely of cartilage. Maruska, K. P. (2001). Sensory biology of elasmobranchs. Cell and Tissue Research, 303(3), 391401. Studnicka, F. K. (1905). Vertebrate | Definition, Characteristics, Examples, Classification Hammerhead sharks have evolved to have more ampullae due to the evolutionary benefits conferred. Think of a fish, any fish at all (well, with the exception of a shark, a skate, or a ray). What are the Economic Benefits of Chondrichthyes? The nervous system in fishes is divided into the central nervous system, containing the brain and spinal cord, and the peripheral nervous system, containing the nerves found throughout the body that originate from the brain or spinal cord.