Swimming & Locomotion

Major types of locomotion in fishes

• Walking – frogfishes

• Crawling – sea robins

• Swimming– most fishes

Antennariidaewarty frogfishAntennarius maculatus

The swimming mechanism

• Muscles• Propulsive waves

Swimming modes

Body musculature

Fin musculature

Swimming modes (body musculature)

Swimmingmodes

Swimming examples

Thunniform – Carangiform swimming

Labriform swimming

Musculature myotomes

Epiaxial or dorsalmuscles

hypaxial or ventralmuscles

Red

Distribution of red muscle

Distribution of red muscle

Ectothermfishes

Bluefin tuna

Skipjack tuna Mako shark

Red muscle

Propulsive wave•Progressive tailward passage•Push force•Reactive force•Forward thrust component•Lift or slippage component

P

R L

T

Progressive swimming undulation wave

Thrust - DragGravity - Lift + Buoyancy

Swimming Forces

Lift Force

• Static lift– Swim bladder– Lipids / Oils

• Dynamic Lift– Pectoral fin rotation– Pectoral hydrofoil shape

Drag forces I

• Frictional or Viscous Drag– Boundary layer: non-moving water layer

that creates friction with surrounding water

– Not speed related– To reduce frictional drag:

• Mucous• Reduction surface area• Ctenoid scales• Placoid scales

Frictional Drag (Flow separation)

Placoid scales

Ctenoid scales

Drag forces II

• Pressure or Inertial Drag– Caused by pressure differences– Drag increases with speed– To reduce pressure drag:

• Streamline shape– Width-length ratio = 0.25– Thickest cross-section 2/5 from mouth– Long and narrow wing-like pectoral fins for lift– Body depressions for retracting paired & median

fins

Pressure and frictional drag

High speed streamlined fishes

Caudal keel

ScombridaeBigeye tunaThunnus obesus

Caudal fin shapes high aspect ratio (thunniform

swimming)

CarangidaeJacks

Caranx melampygus

Caudal fin shapes high/medium aspect ratio (carangiform

swimming)

SerranidaeNassau grouperEpinephelus striatus

Caudal fin shapes low aspect ratio (subcarangiform

swimming)

EsocidaeNorthern pikeEsox lucius

Caudal fin shapes low aspect ratio (subcarangiform

swimming)