Swimming & Locomotion

Major types of locomotion in fishes

• Walking – frogfishes • Crawling – sea robins • Swimming – most fishes

Antennariidae

warty frogfish

Antennarius maculatus

The swimming mechanism

• Muscles • Propulsive waves

Swimming modes

Body musculature Fin musculature

Swimming modes (body musculature)

Swimming modes

Swimming examples Thunniform – Carangiform swimming Labriform swimming

Musculature myotomes

Red Epiaxial or dorsal muscles hypaxial or ventral muscles

Distribution of red muscle

Distribution of red muscle

Ectotherm fishes Red muscle Bluefin tuna Skipjack tuna Mako shark

Propulsive wave •Progressive tailward passage •Push force •Reactive force •Forward thrust component •Lift or slippage component P T R L

Progressive swimming undulation wave

Swimming Forces

Thrust - Drag Gravity - Lift + Buoyancy

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)

Ctenoid scales Placoid 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

Caudal fin shapes high aspect ratio (thunniform swimming)

Scombridae

Bigeye tuna

Thunnus obesus

Caudal fin shapes high/medium aspect ratio (carangiform swimming)

Carangidae

Jacks

Caranx melampygus

Caudal fin shapes low aspect ratio (subcarangiform swimming)

Serranidae

Nassau grouper Epinephelus striatus

Caudal fin shapes low aspect ratio (subcarangiform swimming)

Esocidae

Northern pike

Esox lucius