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Fish swim
1.
2. Contents
Fins
How fish swim
Forces acting on swimming fish
Types of swimming and their modes
How fish generates lift
Forces resisting movement
3. Fins/ Propulsors
• Provide control over movements by directing thrust, supplying
lift and even acting as brakes.
• A fish must control its pitch, yaw, and roll.
1. Caudal fins – provides thrust and control direction
2. Pectorals – acts as rudder, steer up or down, also helps in
stop.
3. Pelvics – mostly control pitch
4. Dorsal fin – control roll
5. Anal fin – stabilizing
4. How fish swim
• A fish swims by contracting and relaxing complex
network of muscles blocks along the sides of its body,
known as ‘Myomeres ’.
• Creates a series of waves travelling down the fish
body.
• The rear part of each wave thrusts against the water
and propels the fish forward.
5. Forces acting on a swimming fish
• Part of fish pushing against water (side
or tail creates normal force (reactive)
pushing in opposite direction.
• Normal force has two components:-
Thrust – It pushes fish forward.
Lift -- It pushes to side.
All lift forces cancels out over one
complete tail stroke.
6. Myomeres
Function :- make body undulate
• Causes body to bend because myomeres on one side
contract, while other member of pair on other side relaxes.
• Seprated by connective tissue, mysopeta that connect to
vertebrae.
— myomeres shaped like sideways “W” - middle
connects forward, sides to back.
— one myomere per vertebra
7. Types of swimming
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 :- wavelength pass down length of body.
Oscillation :- structure (fins) pivots on a base.
8. • Most common “fishy swimming”.
• A wave of muscular contraction from head to tail.
- swings tail back and forth.
- strength & amplitude of contraction increases
toward tail.
• Different fish swim by undulating different parts of
their bodies.
9. ANGUILLIFORM CARANGIFORM OSTRACIFORM
-body flexes one full - These swimmers undulate the - Body rigid, tail oscillates
wavelength, with head acts posterior half of their body .
as fulcrum. Body flexes < 1 wavelength
-Typically slow swimmers - much faster than anguilliform - relatively slow swimmers
swimmers
It is usually seen in fish with Tuna Boxfish
long slender bodies like white sharks Torpedo rays
Eel salmon momyrs
Lampreys jack fish and maco sharks.
Many varieties of
larvae and oar fish.
10. • Rowing (sculling) :-
- It is same as oars...
- power stroke with fin expanded
- return stroke with fin collapsed
• Oscillation :-
- pectoral fins oscillated slowly or rapidly (like a bird)
- generates lift
- requires large mass in pectoral girdle
• Undulation :-
- usually median fins (dorsal and anal)
- sinusoidal waves run down fins
- can also undulate pectoral fins (skates, puffers)
11. • Rajiform :- Thrust generation involves the passing of vertical undulations along the
pectorals that are very large, triangular shaped, and flexible. The fins may also be
flapped up and down.
- likened to the flight of birds. Eg:- rays, skates and mantas
• Diodontiform :- propulsion is achieved by passing undulations down broad pectoral
fins.
- Up to two full wavelengths may be visible across the fins. Eg:- puffer fish
• Amiiform :- swimming is by undulations of a (usually long-based) dorsal fin, while
the body axis is in many cases held straight when swimming.
eg:- african fresh water eel
• Gymnotiform :- since propulsion is obtained by undulations of a long-based anal
fin.
- dorsal fin is usually absent Eg:- knife fish
• Balistiform :- both the anal and dorsal fins undulate to generate the propulsion
forces.
- their median fins are usually inclined relative to each other, while the body
is usually flat and compressed laterally.
eg:- trigger fish
12. a) Modes of BCF swimming
b) Modes of MPF swimming
Shaded areas contribute to thrust generation.
13. How fish generate lift
• The swim bladder acts just like a
balloon – with the ability to control
the amount of gas.
• More gas is added to the swim
bladder to move to a higher level in
the water.
• Gas is released from the swim
bladder to move to a lower position
in the water.
13
14. Inflating the Swim Bladder
• Inflating the swim bladder is an active
process that generally involves a gas gland.
• The gas gland is rich with capillaries and
acts to concentrate oxygen until the
pressure of oxygen in these capillaries is
greater than in the swim bladder.
• Oxygen will then diffuse from capillaries
associated with the gas gland into the swim
bladder, causing it to inflate, and allowing
the fish to rise.
14
15. Deflating the Swim Bladder
• The primary gas in a swim bladder
is oxygen. To maintain a lower
position, the swim bladder must
release some of the oxygen.
• Deflating the swim bladder is a
passive process. Higher pressures
inside the swim bladder force
oxygen to diffuse into the blood
stream in surrounding capillaries.
• This allows the fish to sink to a
lower depth.
15
O2
O2
O2 O2
High
Pressure
O2
16. • Frictional drag: caused by water
molecules sticking to skin
• proportional to: (surface area of
body) x (velocity)
• minimize surface area (be a sphere)
• The slime coat provides a smooth
surface that allows laminar flow and
minimizes frictional drag.
Pressure drag : Caused by pressure
differential between front and back of fish
• minimize by...
-- improving streamlining (fusiform shape, fin
slots)
-- directing flow (caudal keels, finlets, scales)
Form drag: caused by displacement of water
• proportional to:
(cross-sectional area of body) x (velocity2)
• minimize by being slender
Figure from http://www.geocities.com/aquarium_fish/how_fish_swim.htm 16
17. Maneuvers
(butterfly fishes,
damselfishes,
angelfishes)
- slow moving, so drag
& inertia relatively
unimportant
- deep, compressed
bodies that can be
turned quickly
MPF rowing/sculling
Accelerators
(barracuda, pike, giant
sea bass, groupers
- need to overcome
inertia, drag less
important
maximize thrust by
having large surface
area in rear of body
Generates thrust by
BCF undulation
Cruisers
(tunas, mackerels,
marlins, jacks)
Low form and friction
drag due to
streamlined &
smooth body
Higher acceleration
Generate thrust by
BCF undulation
