Lesson 2 (Marine bio)

Reynolds Number

a parameter used to predict flow behavior by calculating the ratio between inertial and viscous forces

Re > 1: inertia forces predominate

Re < 1: viscous forces predominate

2 types of lift based swimming

1. Body and Caudal Fin swimming (BCF)

2. Median and Paired Fin swimming (MPF)

Body and Caudal Fin swimming (BCF)

• Most common form of swimming.

• A wave of contractions from head to tail: swings tail back and forth

• strength and amplitude of contraction increases toward tail

• Different fish swim by undulating or oscillating different parts of their body.

Undulation

waves passing down body or fin

Oscillation

flapping motion

Median and Paired Fin swimming (MPF)

• Other fish have developed alternative swimming mechanisms that involve the use of their median and pectoral fins

• termed median and/or paired fin (MPF) locomotion

• Although the term paired refers to both the pectoral and the pelvic fins, the latter (despite providing versatility for stabilization and steering purposes) rarely contribute to forward propulsion

Advantages of Lift-based Swimming

• High speed – Most efficient for long-distance cruising

• Energy efficient – Requires less energy, once moving, they glide efficiently

• Continuous thrust – Lift provides smooth, steady movement without intermittent

• Low drag – Streamlined bodies and minimal undulation reduce water resistance

Disadvantages of Lift-based Swimming

• Complex musculoskeletal system – Requires specialized skeletal adaptation

• Unable to hover backward – Requires forward movement to generate thrust

Single Caudal Propulsor

• uses only the tail or flukes to generate thrust.

• The body remains relatively rigid while the tail structure moves to propel the animal forward.

• This is distinct from BCF swimming where the body undulates.

• Concentrate all propulsive power in a specialized tail, keep the body rigid, and let the hydrofoil do the work

Sarcomeres consist of two types of myofilaments

• Myosin – (thick filament) contains small protruding heads

• Actin – (thin filament)

• Titin – a protein molecule that holds the myosin filaments from M band to the Z line

Z lines

hold the myofilaments

A band

overlap of actin and myosin

I band

only actin present in this region

H zone

only myosin present in this region

Actin and Myosin

Cross-Bridge Formation

White Muscles

• White muscle makes up about 85% of the muscle mass of fish.

• (aka) fast-twitch muscles or glycolytic muscles

• For high intensity swimming

• Quick short bursts of movement

• Anaerobic activity

• Example: Seabass

Skeletal Muscle Fibre Types: White muscle

• Burst activity: short duration and high intensity

• Less myoglobin

• Fast twitch

• Glycolytic

Red Muscles

• Red muscles makes up to 20% of the muscle mass of fish

• Red muscles are also known as slow-twitch muscle or oxidative muscles

• Red muscles contains myoglobin, capillaries and lots of glycogen and lipids

• For low intensity swimming

• Can also make use of lipids as a source of energy for sustained swimming

• Example: Tuna

Skeletal Muscle Fibre Types: Red muscle

Floating mechanism

• passive → drift with ocean currents

• no muscular effort

• eg: plankton, jellyfish

factor role in floating

• neutrally or positively buoyant

• low density tissues, gels, oils

• flat, spread-out

• move horizontally or vertically due to ocean currents