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L14-15_swimming_11CO - SWIMMING Fish Swimming Overview I How basic vertebrate system is adapted to move through water II Introduction to osteology

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SWIMMING
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Fish Swimming - Overview I. How basic vertebrate system is adapted to move through water II. Introduction to osteology and musculature system in fishes III. Diversity of designs for swimming
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Special features of movement through water No trivial task: i) Water is 800 times denser than air ii) 50 times more viscous than air iii) far lower [O 2 ] for respiration. air 20 %, water < 1% Therefore, fish must be extremely efficient (in movement/energy expended)
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So, system has evolved to: (A) minimize energy requirements (e.g. pike) (B) increase acceleration and speed (e.g. tuna) (C) improve maneuverability (e.g. perch) (D) compromise between and fine tuning of a, b, and c. (a) (b) (c)
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I. Mechanisms of moving through water Motion is a balance between two hydrodynamic forces; those that resist and those that generate propulsion: Resistance = inertia + drag Inertia = energy required to start something in motion Drag = force that acts backwards along the direction of motion; comprised of 2 components: 1) friction drag 2) pressure drag
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I ) Friction drag - ‘stickiness’ of water along body side. Caused by H 2 O molecules bouncing off fish (given forward velocity). Proportional to velocity of water or fish and body surface area . Water flow Boundary layer : thin layer with steep velocity gradient
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II) Pressure drag - caused by distortions of flow around fish’s body. Pressure differences that result from the displacement of water as the fish moves. Net pressure difference between head (high pressure) and tail (low pressure). Proportional to velocity 2 and body shape . Flow separation turbulent wake High pressure Low pressure
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Four ways to minimize drag: i) Fusiform body shape (streamlining) ± reduces pressure drag ii) Mucous/slime ± reduces friction (evidence inconclusive; antibacterial and sunscreen properties more important) iii) Fins tuck into folds in body
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iv) Vortex generators ± placoid and ctenoid scales may have evolved independently in sharks and teleosts, respectively, to retard separation of the boundary layer. Small vortices prevent larger ones and help stabilize the boundary layer. smooth rough
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Lift (lower pressure on top) Propelling the body through the water Two forces that enhance propulsion: lift and thrust . 1) Lift - force perpendicular to direction of motion. Keeps moving object aloft in the water column. Happens when water moves faster over one surface than another. Pressure inversely related to water velocity. Can act both vertically and horizontally. D 1 D 2 Distance: D 1 > D 2 Velocity: V 1 > V 2 Pressure: P 1 < P 2
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– Linear, (directed straight forward) exerted by fish to propel itself. Created in two ways: i) undulatory -- wave of increasing amplitude passes along length of body (head to tail) - Generated by body and tail ii) oscillatory -- structure pivots back and forth on its base Generated by paired fins and caudal fin (e.g., tuna) -- movement from side to side.
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This note was uploaded on 01/10/2012 for the course EEMB 106 taught by Professor Staff during the Spring '08 term at UCSB.

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L14-15_swimming_11CO - SWIMMING Fish Swimming Overview I How basic vertebrate system is adapted to move through water II Introduction to osteology

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