Chordata-Fishes

Channelle Walker
 * __Kingdom Animalia: Chordata-Fishes __**

**Diagnostic characteristics: **

· Mineralized (ossified) Skeletons and Teeth
**Acquiring and Digesting Food: **

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Since fish have acquired jaws and teeth they have been able to slice up and grip food within their mouths. Earlier fish fed mainly on floating food particles or particles on the sea bottom before they developed jaws. Many species of fish have become active predators because of their anatomy (jaws, teeth, and fins). Large sharks and rays are suspension feeders and tend to eat plankton, however, most sharks are carnivores who either tear off part of animals or swallow their prey whole. The digestive tract of many sharks is shorter (proportionately) than those of other vertebrates. Sharks have a spiral valve within their intestines that slows the passage of foodstuff because the valve increases surface area. ======

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Rays, although they are very similar to sharks tend to spent their time eating mollusks and crustaceans at the seafloor; they use their jaws to crush the shells and eat them. ======

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"The digestive systems of fish are similar. All fish have a mouth, oesophagus (throat), areas for absorbing food and nutrients (foregut and midgut) and areas to compact indigestible waste material (hindgut). However, differences among fish can be seen due to different diets. These differences are seen in the mouth, teeth, stomach (if present), and the length of the intestine. Carnivorous fish have a definite stomach (foregut), while herbivorous fish do not have a stomach but instead rely on an extended midgut area. Also, carnivorous fish have extensions to the upper part of their midgut." (AK) (4) ======

**Sensing the Environment: **

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Sharks are known to have very acute senses, their vision is superior, however they cannot differentiate between colors. The nostrils of a shark only function for distinguishing scents, not breathing. The nostrils open into dead end cups (similar to most fish). The shark has regions on their heads in their skin where they can sense electrical fields that are generated by nearby animals who are contracting their muscles. Sharks have a row of microscopic organs down the length of each flank called the lateral line system; the organisms sense changes in the surrounding water pressure. This characteristic is present in most aquatic vertebrates and allows the organisms to identify vibrations. These structures are necessary for many aquatic organisms because they lack eardrums, so sounds are transmitted through vibrations within the water. When the sound is sensed by the body it is transmitted to the inner ear, allowing the fish to hear. "Many Species of fish can also sense low levels of electric current through networks of electrosensory cells. Sharks can sense the current involved in the beating heart of sting ray deep below covered by a layer of sand or moving prey very far away (JS)[|(6)]" ======

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Fish see a very different view of the world than other organisms do. Their unique spherical lens in their eye allows for a greater scope of vision- the famous "fish-eye lens" allows the fish to see more at a time, (although at the cost of its close frontal vision), as the two wide-angle eyes are on opposite sides, facing opposite directions. As a result, a fish may see a predator far away, but fail to see some food near its mouth. This is why many fish sweep their heads from side to side. Since fish live in water, their view of colors are extremely distorted, as a result of the dense and scattering medium that they live in. Fish eyes, like human eyes, do have rods and cones, but because of light's scarcity in many parts of the ocean, many, many fish have more rods than cones. Other fish, on the other hand, have been shown to perceive ultra violet light, a type unseen by man. (TM)(8) ======

**Locomotion: **

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Sharks are rapid swimmers, but they do not maneuver well. The strong swimming muscles mainly in the tail and fin propel them forward while the dorsal fins stabilize. The paired pelvic and pectoral fins provide lift which is necessary because since sharks are so dense, if they were to stop swimming they would sink in the water. Sharks gain some buoyancy because massive amounts of oil are stored within their livers. ======

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Rays are similar to sharks but their pectoral fins are extremely large in proportion to their body size and they are used to propel the animal through water, similar to wings to a bird in flight. ======

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Most bony fish have a sliminess to them in order to help them swim. They have glands within their skin that secretes a mucus that reduces the amount of drag that occurs during swimming. Bony fish are relatively good at maneuvering because their fins are more flexible, which is better for propelling and steering the fish. Bony fish have a swim bladder which is an adaption that rays and sharks both lack. The air sac helps with the buoyancy of the fish because when gas transfers between the sac and the blood the levels of inflation within the sac change accordingly. Most bony fish, unlike the shark, and remain motionless in the water because of this swim bladder. ======

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All fish have fins, and there are several different types of fins. The size and location of the fins are closely related to the lifestyle and environment of the fish. Pectoral fins are usually used for turning, and are used to produce power when the fish is swimming. Interestingly, pectoral fins can also sense the environment; they can be used for taste and touch. Pelvic fins are used for stability, so the fish remains upright while swimming. Pelvic fins are also used to slow the swimming of bony fishes. The dorsal fin ranges from a single fin to multiple fins. In bony fish, it is used when the fish suddenly wants to change direction while swimming. Like the pelvic fin, it is also used to maintain stability. The caudal fin, also known as the tail, is used mainly to propel the fish through the water. The shape of the caudal tail is also shaped in a way that benefits the lifestyle of the fish. "Crescent-shaped tails" are found on constantly-moving, fast-swimming fish. "Forked tails" are found on fast-swimming, though not always constantly-moving fish. The deeper the fork, the faster the fish can swim. "Rounded tails" are found on slow-swimming fish, but they are capable to reaching short bursts of speed when neeed. (RG) [|(9)] ======

**<span style="color: #1f497d; font-family: 'Calibri','sans-serif'; font-size: 14pt; line-height: 115%;">Respiration: **

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Gills are used in the respiration of chordata-fish; gills are outfoldings of the surface of the body of many aquatic organism that are suspended in the water. The gills of most marine animals are on one specific part of the body but some aquatic organisms have gills covering the surface of their bodies. The surface area of the gills of a marine organism is usually much larger than the surface area of the rest of the animal. ======

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Since sharks pretty much swim continuously it ensures the flow of water into their mouths and out through the gill, the area of gas exchange. When the sharks and rays are resting on the seafloor they use the muscles of their jaws and pharynx to pump water over the gills so they can breathe. ======

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Bony fish breathe because they draw water over four or five pairs of gills. The gills are in chambers covered by a protective flap, the operculum. Water is draw into the mouth of the fish, through the pharynx and out through the gills. This occurs due to the movement of the operculum and contraction of the muscles that surround the chambers of the gills. Bony fish can breathe without continuous swimming because of this process. The swim bladder that bony fish now use for buoyancy evolved from balloon-like lungs which may have been used by earlier bony fish to supplement gas exchange by gills in shallow water. The swim bladders may have also helped in more swamp-like territories because of the low oxygen content. ======

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There are a species called lungfish which inhabit the Southern Hemisphere, usually in stagnant ponds and swamps, who rise to the surface to gulp air into their lungs. They also have gills, which are the main organs for gas exchange in Australian lungfish. ======

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Water is the respiratory medium for aquatic organisms which has its up sides as well as it's down sides. On the positive side the cells membranes of the respiratory surface are always moist because the gills are surrounded by water. Negatively oxygen concentrations in water are lower; not to mention more tropical saltwater fish are exposed to less dissolved oxygen. ======

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A process that helps gills be so effective in these environments is ventilation. During respiration the flow of the water (respiratory medium) over the gills (respiratory surface) is increased. If ventilation did not occur than a region with high carbon-dioxide and low oxygen concentations would form around the gill, which would make the gill an ineffective respiration pathway. ======

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When water enters the mouth of fish, sharks, etc. it is passes through the slits in the pharynx, flows over the gills and then exits the body of the fish that is the process of ventilation. This presents the other downside to respiration with gills because fish spend a lot of energy ventilating their gills due to the low concentration of oxygen in the water. ======

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Fish have a countercurrent gas exchange system which is very efficient. It reduces the amount of energy needed for ventilation because of the arrangement of the blood capillaries. Oxygen is transferred to the blood easily because the blood flows in the opposite direction of the water when it passes the gills. Blood moves through a gill capillary and becomes more oxygenated and at the same time it meets the water, which has even higher oxygen concentrations because the water is just meeting the gills. The gills can retrieve more than 80% of dissolved oxygen from the water when it passes over the respiratory surface. ====== <span style="color: #4bacc6; font-family: Arial,sans-serif; font-size: 10pt; margin: auto 0in;"> (GR) Fish respiratory system **<span style="color: #1f497d; font-family: 'Calibri','sans-serif'; font-size: 14pt; line-height: 115%;">Metabolic Wa ****<span style="color: #1f497d; font-family: 'Calibri','sans-serif'; font-size: 14pt; line-height: 115%;">ste Removal: **

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<span style="color: #008080; font-family: Arial,Helvetica,sans-serif;">Ammonia excretion is most common in aquatic species because ammonia can only be tolerated at low concentrations and is very soluble, so the organisms that excrete it need a lot of water. Ammonia passes through membranes and are lost via diffusion because of the surrounding aquatic environment. Most ammonia within fish are lost as ammonium ions through the epithelium of the gills. The kidneys of the fish excrete small amounts of nitrogenous wastes. ======

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<span style="color: #008080; font-family: Arial,Helvetica,sans-serif;">In freshwater fish transport epithelia in the excretory organs have the functions of removing metabolic waste as well as maintaining water balance. The epithelium of the gill excretes ammonium ions in exchange for sodium ions which helps maintain a salt balance within the body. ====== (MLK)[|7] **<span style="color: #1f497d; font-family: 'Calibri','sans-serif'; font-size: 14pt; line-height: 115%;">Circulation: **

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<span style="color: #4bacc6; font-family: Arial,Helvetica,sans-serif;">Fish have a two-chambered heart and a single circuit of blood flow. They have one atrium and one ventricle. Blood is pumped from the ventricle and travels to the gills which it becomes oxygenated and releases carbon-dioxide, this entire process is gill circulation. The capillaries of the gills then converge into a vessel that carries the oxygenated blood to other parts of the fish's body, this process is called systemic circulation. The now deoxygenated blood returns to the atrium of the heart. ======

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<span style="color: #4bacc6; font-family: Arial,Helvetica,sans-serif;">In fish blood must pass through two capillary during each of the two circuits. When the blood flows through a capillary bed the blood pressure drops. Because of the drop in blood pressure the oxygenated blood flows to the systemic circulation relatively slowly. ======

This diagrams the circulatory system of fishes. (DB) (3)

**<span style="color: #1f497d; font-family: 'Calibri','sans-serif'; font-size: 14pt; line-height: 115%;">Self Protection: **

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<span style="color: #008080; font-family: Arial,Helvetica,sans-serif;">The male three-spined stickleback fish is a very territorial fish and has no problem attacking other males that enter his territory. The red-belly of the male intruder sends an alert to the other male stickleback fish that an attack is necessary. "Some of the most interesting fish, from the point of view of natural history, which we encountered were the star-gazers ( Uranoscopus) . They are rather clumsily built and have a large angular head with small eyes placed close together on the top and a completely vertical mouth. They have the habit of burying themselves in the sand with only mouth and eyes showing. They live on small animals, which they entice by sticking out from the mouth a red or white filament or skin-flap which resembles a worm. They are well protected both by their grayish color and by their ability to inftict a painful shock by means of electric organs behind the eyes, formed by a modification of part of the eye musculature." [MS] [|**2**][Some fish like the Japanese fungu (type of puffer fish) have poison in their systems that causes the eater of the fish to die very suddenly and painfully. The outside of the Japanese fungu have spikes that like a porcupine protect again enemies. (MP) [|**5**]]In other cases fish, such as the electric eel, send powerful electrical shocks for self defense.(KS)(6) Many fish have coloring called "countershading", where fish have lightly colored ventral sides and darkly colored dorsal sides. This coloring is used as a type of camoflage to hide from predators: where seen from above they blend in with the dark ocean depths and when seen from below they blend in with the light filled waters above. (KS)7 These behaviors are some of the self protection attributes that some fish have inorder to protect themselves and their territory. ======

**<span style="color: #1f497d; font-family: 'Calibri','sans-serif'; font-size: 14pt; line-height: 115%;">Osmotic Balance: **

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Osomoregulation is only about 5% of the resting metabolic rate for bony fish because water and solutes can easily move throughout their membranes due to their aquatic environment. Osoregulators for example tilapia, an African bony fish, is able to adjust any salt concentrations between fresh water and 2,000 mosm/L water, which has twice the salt concentration of seawater. ======

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Total osmolarity is the sum of the concentrations of all the dissolved substances. In hagfish the total osmolarity is the same as the seawater, but the specific solutes have different concentrations. ======

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Fish are osmoregulators and the ocean tends to be a dehydrating envrionment because it has a higher salt concentration than the internal fluids of the fish. Water tends to be lost from the internal body of the fish by osmosis, the diffusion of water. Marine fish lose water through their skin, especial through their gills quite often. In order to balance out the water loss, fish drink a high quantity of seawater. The salt from the seawater intake as well as the salt entering their bodies through diffusion is removed through the gills by active transport. ======

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Sharks and other cartilaginous fish have different methods of osmoregulatory. Internally they have a much lower salt concentration than of seawater so salt tends to diffuse into their bodies mainly through the gills. Sharks' kidneys remove some of the salt while the rest is excreted by the rectal gland or feces. Marine sharks do not have a large or continuous water loss like bony fish despite the low internal concentration of salt. Sharks have high concentrations of urea as well as other solutes in their body which makes them hyperosmotic to seawater. Water slowly enters the body of a shark through osmosis and in food and this water is disposed of through urine. ======

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Freshwater fish are gaining water and losing salt through diffusion because the concentration of salt internally for freshwater fish is much higher than that of the water. Most freshwater fish maintain water balance by excreting a lot of diluted urine and obtaining the lost salt through food and active uptake from their surroundings. ======

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Other fish that migrate between seawater and freshwater environment such as salmon change their osmoregulatory processes. When in the saltwater the salmon and other migrating fish regulate just as the bony fish by drinking seawater and releasing salts through their gills. When the fish migrate to the freshwater they act like freshwater fish and stop drinking water and produce diluted urine. The migrating fish also intake salt through their environments and food while in the freshwater. As the migrating fish change environments they change their process of osoregulation accordingly. ====== **<span style="color: #1f497d; font-family: 'Calibri','sans-serif'; font-size: 14pt; line-height: 115%;">Temperature Balance: **

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<span style="color: #008080; font-family: Arial,Helvetica,sans-serif;">Some marine fish are ectothermic organisms usually referred to as "cold-blooded" while others are endothermic the "warm-blooded" organisms. Ectothermic marine fish tend to live in water with a relatively stable temperature so their body temperatures don't usually fluctuate too much. Endothermic fish usually maintain a high and stable internal temperature even as the environment changes. =====

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<span style="color: #008080; font-family: Arial,Helvetica,sans-serif;">Most fish have an internal temperature within 1 or 2 degrees Celsius of the water temperature. Most of the heat that is generated from the muscles is lost to the water in the aquatic environment when the blood passes through the gills. Some endothermic fish, usually the larger and more powerful ones, such as the swordfish, or great white shark have circulatory adaptations that retain heat. In these larger fish, arteries send most of the cold blood from the gills to tissues directly beneath the skin. The main swimming muscles in these fish are several degrees warmer than the surface tissue, which helps maintain internal heat because the deeper tissues are warmer. All fish lose heat to the surrounding water when the blood passes through the gills, but some species of fish have better adapted to this. Most of the blood that moves away from the gills only stays on the surface because the core of the body wants to remain warm =====

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<span style="color: #008080; font-family: Arial,Helvetica,sans-serif;">In the ectothermic fish the surface of the bodies are about the same temperatures as the surrounding water. In some other species of fish there are specialized organs that warm just the eyes or the brain. =====

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__Review Questions:__
<span style="color: #000000; font-family: Arial,Helvetica,sans-serif; font-size: 10pt; font-weight: normal;">1) In what form do fishes excrete their nitrogenous wastes? How do they excrete most of this waste? How does excreting this waste help the fish to maintain a salt balance within the body? (SD)

<span style="color: #000000; font-family: Arial,Helvetica,sans-serif; font-size: 10pt; font-weight: normal;">2) Briefly describe the circulatory system of a fish, and explain how it differs from that of a mammal. (NI)

<span style="color: #000000; font-family: Arial,Helvetica,sans-serif; font-size: 10pt; font-weight: normal;">3) Describe the respiratory system of fish. What processes/characteristics make it efficient? (AK)

<span style="color: #000000; font-family: Arial,Helvetica,sans-serif; font-size: 10pt; font-weight: normal;">4) How do the larger fish, such as the shark or the swordfish, maintain an internal body temperature? How does this compare with the ways that amphibians maintain their body temperatures?(CC)

<span style="color: #000000; font-family: Arial,Helvetica,sans-serif; font-size: 10pt; font-weight: normal;">5) What are/is the benefits and process of gills in fish? (AC)
<span style="color: #000000; font-family: Arial,Helvetica,sans-serif; font-size: 10pt; font-weight: normal;">6) What are the differences in acquiring and digesting food between carnivorous fish and herbivorous fish? (SM)

** Sources: ** <span style="color: #000000; font-family: 'Times New Roman',Times,serif; font-size: 16px; line-height: 32px; margin: auto 0in;">1. Reece, Jane B., and Neil A. Campbell. // Campbell Biology. // San Francisco: Pearson Benjamin Cummings, 2009. Print. <span style="color: #000000; font-family: 'Times New Roman',Times,serif; font-size: 16px; line-height: 32px; margin: auto 0in;">2. [] <span style="color: #000000; font-family: 'Times New Roman',Times,serif; font-size: 16px; line-height: 32px; margin: auto 0in;">3. []

4. http://www.aqualex.org/elearning/fish_feeding/english/digestion/structure.html 5. [] 6.[|http://faculty.bennington.edu/~sherman/the%20ocean%20project/shark's%20electric%20sense.pdf] 7. [] 8. [] 9. [] 10. [|http://www.cbu.edu/~seisen/LcEx02Fa2008EssayAnswers.htm] 11. http://www.google.com/imgres?imgurl=http://naturescrusaders.files.wordpress.com/2009/02/gill_pic1 (GR)