Movement in water

Aim nfloating or sinking njet propulsion nswimming u slow u fast nmechanics and shape of an optimal design nhow fish move forwards

References nSchmidt - Nielsen K (1997) Animal physiology nMcNeill Alexander R (1995) CD Rom How Animals move nWeb links: see:

In water ndensity of flesh similar to that of water u Skeletal support not so important nSwimming more efficient than running! nmajor cooling effect

density n= mass / volume nair 1 kg /m 3 ndistilled water 1000 kg / m 3 nsea water 1030 kg / m 3 nbut tissues denser than water u muscle 1060 kg / m 3 u bone kg / m 3

Floating ndensity of fish > water nless dense than water u jellyfish : jelly u shark liver : squalene nswim to generate lift u sharks ngas store u Physalia u Nautilus oxygen u teleost swimbladder

Sharks have to swim… nlift from aerofoil shape of pectoral fins nasymmetric tail moves more water on top u forces water down and shark up

Floating with CO n Physalia u makes carbon monoxide

Floating with gas nNautilus oxygen nrigid chamber u x-ray mostly gas u last still water filled

Swimbladders nfull of oxygen nX-ray of butterfly fish

Swimbladders at depth nPressure increases with depth u 1 atm = 10 m u Swimbladders get smaller, u give less buoyancy nfish unstable with depth

How fill swimbladder 1.secrete lactic acid into blood n forces hb to release O 2 [Root effect] 2.run a counter-current exchanger n keep O2 in blood of rete mirabile

Blood flow in rete flow lactic acid

Oxygen flow in rete ncounter current u can fill swimbladder at 100 atm bladder

Summary so far nbuoyancy can be solved u low density u active gas secretion u swimming ncarry a cost u larger (more drag from wider body) u difficult to stay stable nwhat is the optimal solution?

Jet propulsion nconservation of momentum = m*v nmass of fish * velocity of fish = mass of water * velocity of water u squid F contract mantle u dragonfly larvae

Paddling / rowing u ducks u beetle larvae u frogs swimming

Paddling / rowing ndepends on conservation of momentum u ducks u beetle larvae u frogs swimming

Drag nReynolds number gives an estimate of drag nRe = length * speed * density / viscosity u for air, density / viscosity = 7*10 4 s / m 2 u for water; density/ viscosity = 10 6 s/m 2 nfriction nturbulence

Reynolds number nRe < 1 no wake u e.g. protozoan nRe < 10 6 flow is laminar u e.g. beetle nRe > 10 6 flow is turbulent u e.g. dolphin nDrag depends on shape nDrag reduced by up to 65% by mucus

Swimming nUndulations u side to side (fish) u up down (whales, dolphins) nhow do undulations propel you forwards? nRowing u fins (reef fish) u legs (insects e.g. beetle larvae & birds)

How does a fish move?

How are swimming movements produced? nMyomere arrangement

Myomere cross-section nWhite muscle contracts anaerobically, u using glucose for fuel and producing lactate. nRed muscle contracts aerobically, u using lipid for fuel and producing CO 2.

Design for minimal drag ntuna or swordfish: u highly efficient for high-speed cruising in calm water ntorpedo-shaped body nnarrow caudal peduncle nlunate, rigid fins

Why don't all fish look like that? nThe design is highly inefficient: u In naturally turbulent water (streams, tidal rips, etc.) u for acceleration from stationary u for turning u for moving slowly u & especially for lying still

Size and shape easy to turn - rigid slow - fast head moves - head still power from whole - power from tail muscles pull via tendons on tail fin

Ambush predators nkeep head still u long body/dorsal fins nrapid start u flexible body, plenty of muscle u large tail fin nbarracuda npike

Design for manoeuvrability nSmall items don't move fast, but require delicate, focused movements for capture. nA short, rounded body with sculling or undulating fins. nCompressing the body laterally provides a wide surface to exert force on the water

Optimal design? nNo one optimal design nefficient energetics isn’t all nmaximum speed isn’t all

How is thrust generated? nthrust = momentum / time nanguilliform

How else is thrust generated? ntail movement nCarangiform u tail generates symmetric vortex street note rotation

How else is thrust generated? ntail movement acts like a hydrofoil u thunniform u cetaceans u penguins

Flying not swimming ntail movement acts like a hydrofoil ngenerates lift and drag u drag acts in line of motion u lift acts perpendicular (normal) to drag drag lift total

Summary ngravity less important nbuoyancy can be solved nthrust from u paddles [fins] u body u tail nno one optimal solution? npoint to ponder: swimming in protozoa