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The Problems of Fish Oceans 11 Introduction • Seawater may seem like an ideal habitat, but living in it does present difficulties. – – – – How can fish best move through water? Why don’t fish sink? How can fish breath underwater? How do they deal with the salinity of seawater? – How can predators be avoided? Movement Shape and Propulsion: • How can fish best move through water? – Fish usually have a streamlined shape (this reduces energy loss to drag) – Faster swimming fish have tapered, torpedo like body plans – Swimming occurs by S-shaped waves that pass through body. • *FYI - Swordfish and Marlin can reach speeds of 120km/hr! • http://www.youtube.com/watch?v=Viu9gql djrc&feature=related Bluefin Tuna Maintenance of Level: • Why don’t fish sink? – Fish are more dense than water – Swim Bladders provide enough buoyancy to offset the animal’s weight (only found in bony fish) – The amount of gas in the bladder changes with depth Swim Bladder Gas Exchange: • How can fish breath underwater? – Fish take in water (containing Oxygen) in through their mouth – Water is pumped past fin gill membranes (where oxygen is picked up and carbon dioxide is dropped off) – Water exits through gill slits – Circulatory system transports blood through body Gills Osmotic considerations: Osmotic: The tendency of water to pass through a membrane into a solution where the solvent concentration is higher, thus equalizing the concentrations of materials on either side. • How do they deal with the salinity of seawater? – In bony fish special glands in gills excrete excess salt – Sharks and rays supplement internal fluids with urea (occuring in bodily fluids as a product of protein metabolism) Defence: • How can predators be avoided? – Sight and hearing are usually very well developed – Lateral line system can detect low-frequency vibrations – Camouflage: http://www.youtube.com/watch?v=HSPptPhbFVc – Countershading – Schooling behaviour • *FYI Flying fish can simply disappear by accelerating rapidly, leaping into the air and spreading their fins to act like wings! • http://www.youtube.com/watch?v=gAjzH0vWSIA