Types of Swimming

Swimming I. Types of swimming II. Methods for generating propulsion III. Forces resisting movement IV. Adaptations to different swimming modes V. Relationships between swimming and ecology Fishes swim in lots of different ways... I. Types of swimming • how much does the body flex? A. Anguilliform (eel-like) • body flexes one full wavelength or more B. Carangiform (jack-like) • body flexes < 1/2 wavelength — fast — Thunniform (extreme) C. Ostraciform (boxfish-like) • body rigid, tail oscillates — slow These are extremes - there is complete gradation between the 3 types I. Types of swimming • a more informative classification (Paul Webb) based on ... — body parts used — type of propulsive force generated A. Body and Caudal Fin swimming (BCF) 1. undulation 2. oscillation B. Median and Paired Fin swimming (MPF) 1. undulation 2. oscillation 3. rowing/sculling undulation: wavelengths pass down length of body (or fin) II. Generating propulsion A. BCF swimming 1. BCF undulation • most common • “fishy swimming” • a wave of muscular contraction from head to tail – swings tail back and forth – strength & amplitude of contraction increase towards tail oscillation: structure (fin) pivots on a base Keep in mind that a fish might need to do different things while swimming: • cruise • accelerate • maneuver • part of fish pushing against water (side or tail) creates normal force (reactive) pushing in opposite direction Biomechanics: how does the fish cause its body to undulate? • muscles provide power • bones act as levers • nerves trigger muscles – since amplitude is greatest at tail, thrust is greatest there • normal force has two components: - thrust pushes fish forward - other component pushes to side — side to side component is cancelled out since body and tail move side to side 1. Bones • head acts as fulcrum (heavy) • vertebral column is incompressible, but flexible 2. Muscles • divided into sections, myomeres (myotomes) 1 2. Muscles Form • divided into sections, myomeres (myotomes) myomere • separated by connective tissue, myosepta, that connect to vertebrae — myomeres shaped like sideways “W” - middle connects forward, sides to back — one myomere per vertebra Form Form • myomeres are layered on top of each other and link vertebrae to skin and other distant vertebrae through tendons — muscle mass divided into 4 blocks: • a septum divides muscle on one side from other • another septum divides muscle on one side into upper (epaxial) and lower (hypaxial) halves • layers of myomeres looks like rings in cross section Connect to vertebrae Connect to skin Epaxial Tuna Hypaxial Function: make body undulate • paired myomeres are sequentially innervated by spinal nerves (one pair per vertebra) • causes body to bend because myomeres on one side contract, while other member of pair on other side relaxes • wave of contraction passes down length of body, increasing in amplitude http://www.oeb.harvard.edu/lauder/videos.htm Startle response • a special way to generate very rapid acceleration – normal sequence of innervation of myomeres aborted – all myomeres on one side contract at once (then same on other side) – generates 2 big contractions – body bends into a “C” instead of “S” Ø done by Mauthner cells, giant axons, that run length of body (not found in Chondrichthyes) 2 Two types of muscles: • red Differences between red and white muscle in fishes - continuous, moderate paced swimming (e.g., tunas) attribute red muscle white muscle - efficient, sustained aerobic metabolism - more blood, O2, and energy stores (fat) shape of fiber slender stout contraction weaker, slower stronger, faster blood supply abundant sparse • white - bursts of fast swimming (e.g., flounders) Can tell swimming behavior by amount of red muscle in flanks: O2 binding pigment myoglobin none mitochondria abundant sparse fat content high low O2 consumption high (6-7x) low mass small large Red muscle placement in tunas, lamnids, and other fish nested myomere cones Behavioral group % red muscle bottom sitters near 0 floater 7-10 continuous swimmers 11-20 • red muscle sits just under the skin in most fishes • in tunas and lamnid sharks, continuous swimmers that retain body heat and metabolically function at higher than ambient temperatures, red muscle is buried deep • tunas and sharks have elongated myomeres = more overlapping rings in cross section Myomere length and red muscle placement is different in tunas than in other fishes Non-Thunniform • each myomere extends only 6-8% of body length Continuous swimmers with lots of red muscle often use a different mechanism to generate propulsion… • red muscle under surface of skin BCF oscillation - propulsion generated by lift - tunas and mackerels • tendons connect myomeres to adjacent vertebra (e.g. vertebra 5 connects to 6) Thunniform • each myomere extends 20-25% of body length Red muscle • red muscle internal Tendon • long tendons project muscle force from each vertebrae to the tail (e.g. vertebra 1 connects to 10) 3 BCF oscillation • narrow caudal peduncle and lunate tail (“wing on a stick”) • fins have high aspect ratio (measure of lift per unit area) Aspect ratio = S2/A where S = length of fin A = surface area of fin BCF oscillation • how lift is generated for propulsion: – tail moved from side to side to positions with positive angles of attack low pressure lift A B - high aspect ratio reduces drag, too high pressure • myosepta specialized into tendons • particle A has to go farther -- therefore A must go faster - allows rapid beating of tail (up to 10 beats/second) • causes lower pressure on A’s side of fin • generates lift towards A’s side Longer distance along front edge ⇒ faster water velocity ⇒ less pressure ⇒ lift in horizontal direction II. Generating propulsion A. BCF swimming B. MPF swimming 1. Rowing (sculling) 2. Oscillation 3. Undulation http://video.google.com/videoplay?docid=312259830463034721 http://www.arkive.org/yellowfin-tuna/thunnus-albacares/video-00.html MPF swimming: MPF swimming: 1. Rowing (sculling) 1. Rowing (sculling) 2. Oscillation • same as oars... — power stroke with fin expanded • pectoral fins oscillated slowly or rapidly (like a bird) — return stroke with fin collapsed • generates lift - requires large muscle mass in pectoral girdle requires: • strong, complex pectoral girdle • good nervous control • large muscles for those who swim lots (wrasses, parrotfish) http://www.youtube.com/watch?v=KVVXGtNN35E http://www.youtube.com/watch?v=QOthel4LTmQ 4 MPF swimming: 1. Rowing (sculling) 2. Oscillation 3. Undulation - usually median fins (dorsal, anal) - sinusoidal waves run down fins - can also undulate pectoral fins (skates, puffers) http://www.youtube.com/watch?v=geajxS37mgg Median & paired fins are also used to: • stabilize • maneuver roll • caudal fin: rudder yaw III. Forces resisting movement: • inertia - energy to start body in motion • drag - force that pushes back against direction of motion pitch • dorsal & anal: prevent roll • pectorals: - particularly important to fish because… control yaw (side to side) used to brake sometimes used to generate lift • water is 800x more dense than air • water is “sticky” (viscous) • pelvics: control pitch (up/down orientation) by generating lift - three components: 1. form drag 2. friction drag 3. pressure drag - evolutionary trend for pectorals and pelvics to move closer to center of gravity - allows for precise maneuvering Drag: Drag: Form drag: caused by displacement of water • proportional to: (cross-sectional area of body) x (velocity2) Friction drag: caused by water molecules sticking to skin • proportional to: (surface area of body) x (velocity) • minimize surface area (be a sphere) • minimize by being slender 5 Drag: Flow direction by vortex generators Pressure drag: caused by pressure differential between front and back of fish (ultimately caused by turbulent vortices) • small vortices can prevent larger ones – placoid and ctenoid scales may have evolved independently in sharks and teleosts – possibly because they retard separation of the boundary layer • minimize by... -- improving streamlining (fusiform shape, fin slots) smooth skin -- directing flow (caudal keels, finlets, scales) W L L/W > 4-5 for laminar flow rough skin Cruisers (tunas, mackerels, marlins, jacks, lamnid sharks) IV. Adaptations to different modes of swimming - tradeoffs • always cruising… don’t need to overcome inertia • maneuvering relatively unimportant — minimize drag — maximize efficiency compare 3 extremes: • cruisers • accelerators • maneuvers Cruisers (tunas, mackerels, marlins, jacks) fins fold into grooves on body Lunate C fin falcate D minimize drag: • form drag: finlets - streamline - minimize body motion • friction drag: - smooth surface: small or no scales - lunate tail reduces “wetted surface area” • pressure drag: - slender caudal peduncle - flow fences: caudal keels - pointed fins - microturbulence: finlets and scales Disadvantages: 1. poor quick start 2. poor turning 3. poor hovering Smooth, scaleless skin keel falcate A heavily muscled fusiform body 6 Endothermy in fishes Cruisers salmon shark (Lamnidae) • maximize efficiency endothermy - muscles are more efficient at higher temperatures (3x more power for every 5˚ C) • some fish (bluefin tuna) can maintain muscles at up to 14˚ C warmer than water achieved by: • having red muscle close to body core • using countercurrent heat exchangers Accelerators (barracuda, pike, giant sea bass, groupers) - typically ambush prey - need to overcome inertia, drag less important • generate thrust by BCF undulation • maximize thrust by having large surface area in rear of body Microscopic view of cross section through countercurrent heat exchanger of a tuna. Arteries have thicker walls and veins thinner walls Maneuvers (butterflyfishes, damselfishes, angelfishes) - slow moving, so drag & inertia relatively unimportant - deep, compressed bodies that can be turned quickly • MPF rowing/sculling • paired fins placed around center of gravity • lots of white muscle, little red, high overall muscle mass V. Relationship between swimming and feeding ecology Webb’s hypothesis: swimming specializations can be explained by distribution of food 1. Food patchy (& widely dispersed) ⇒ cruiser 2. Food uniformly abundant a. evasive prey ⇒ accelerators b. non-evasive prey ⇒ maneuvers Two criticisms of this hypothesis: 1. Isn’t avoiding predators more important than feeding? 2. Isn’t mouth structure more important for feeding success than swimming mode? (Karl Leim) 7