HOW DO FISH SWIM

Contents

Fins How fish swim Forces acting on swimming fish Types of swimming and their modes How fish generates lift Forces resisting movement

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 direction2. Pectorals – acts as rudder, steer up or down, also helps in

stop.3. Pelvics – mostly control pitch4. Dorsal fin – control roll 5. Anal fin – stabilizing

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.

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.

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

Types of swimmingA. 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.

Body and Caudal fin swimming (BCF)

• 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.

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 swimmersIt 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.

Swimming modes of BCF Propulsion

Median and paired fin swimming

• 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)

Swimming modes of MPF Propulsion• 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

a) Modes of BCF swimmingb) Modes of MPF swimmingShaded areas contribute to thrust generation.

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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.

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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.

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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.

O2

O2

O2

High Pressure

O2 O2

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Drag Forces

• 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.

 

Figure from http://www.geocities.com/aquarium_fish/how_fish_swim.htm

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

Different types of swimmers

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

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REFERENCES

– http://www.amonline.net.au/FISHES/students/dissect/swimbladder.htm

– http://lookd.com/fish/swimming.html– http://www.fisheriesmanagement.co.uk/index.htm– http://www.scienceandthesea.org/index.php?

option=com_frontpage&Itemid=1– http://lookd.com/fish/index.html– https://www.tpwd.state.tx.us/– https://googleimages.com

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AKASH KUMAR BHANDARI A3MB13 11MEB325