Movement in water
Aim floating or sinking jet propulsion swimming
slow fast
mechanics and shape of an optimal design
how fish move forwards
References Schmidt - Nielsen K (1997) Animal
physiology McNeill Alexander R (1995) CD Rom
How Animals move Web links: see:http://biolpc22.york.ac.uk/632/movelectures/
water/
In water density of flesh similar to that of water
Skeletal support not so important Swimming more efficient than running!
major cooling effect
density = mass / volume air 1 kg /m3 distilled water 1000 kg / m3
sea water 1030 kg / m3
but tissues denser than water muscle 1060 kg / m3
bone 1500-2000 kg / m3
Floating density of fish > water less dense than water
jellyfish : jelly shark liver : squalene
swim to generate lift sharks
gas store Physalia Nautilus oxygen teleost swimbladder
Sharks have to swim… lift from aerofoil shape of pectoral fins
asymmetric tail moves more water on top forces water down and shark up
Swimbladders at depth Pressure increases with
depth 1 atm = 10 m Swimbladders get
smaller, give less buoyancy
fish unstable with depth
How fill swimbladder1. secrete lactic acid into blood
forces hb to release O2 [Root effect]
2. run a counter-current exchanger keep O2 in blood of rete mirabile
Summary so far buoyancy can be solved
low density active gas secretion swimming
carry a cost larger (more drag from wider body) difficult to stay stable
what is the optimal solution?
Jet propulsion conservation of momentum = m*v mass of fish * velocity of fish
= mass of water * velocity of water squid
contract mantle dragonfly larvae
Drag
Reynolds number gives an estimate of drag Re = length * speed * density / viscosity
for air, density / viscosity = 7*104 s / m2
for water; density/ viscosity = 106 s/m2
friction
turbulence
Reynolds number Re < 1 no wake
e.g. protozoan Re < 106 flow is
laminar e.g. beetle
Re > 106 flow is turbulent e.g. dolphin
Drag depends on shape Drag reduced by up to
65% by mucus
Swimming Undulations
side to side (fish) up down (whales, dolphins)
how do undulations propel you forwards?
Rowing fins (reef fish) legs (insects e.g. beetle larvae & birds)
Myomere cross-section White muscle contracts anaerobically,
using glucose for fuel and producing lactate.
Red muscle contracts aerobically, using lipid for fuel and producing CO2.
Design for minimal drag
tuna or swordfish: highly efficient for high-speed cruising
in calm water torpedo-shaped body narrow caudal
peduncle lunate, rigid
fins
Why don't all fish look like that?
The design is highly inefficient: In naturally turbulent water (streams,
tidal rips, etc.) for acceleration from stationary for turning for moving slowly & especially for lying still
Size and shape
easy to turn - rigidslow - fast
head moves - head stillpower from whole - power from tail
muscles pull via tendons on tail fin
Ambush predators keep head still
long body/dorsal fins rapid start
flexible body, plenty of muscle large tail fin
barracuda pike
Design for manoeuvrability
Small items don't move fast, but require delicate, focused movements for capture.
A short, rounded body with sculling or undulating fins.
Compressing the body laterally provides a wide surface to exert force on the water
How else is thrust generated?
tail movement Carangiform
tail generates symmetric vortex street
noterotation
Flying not swimming tail movement acts like a hydrofoil generates lift and drag
drag acts in line of motion lift acts perpendicular (normal) to drag
draglifttotal