Lecture 4 -Buoyancy and Locomotion in Fish

ichpthyology

What is Archimedes’ Principle?

Buoyancy is the upward force exerted by a fluid that opposes the weight of an object submerged in it.

What is neutral buoyancy?

A state where buoyant force equals gravitational force, allowing a fish to remain suspended in water.

What are the three main strategies to achieve buoyancy?

Reducing body density, using lipids, and gas-based systems (swim bladders).

How do fish reduce body density?

By reducing ossification, losing heavy dermal armor, and using low-density tissues like cartilage or lipids.

: What role do lipids play in buoyancy?

Lipids like squalene are less dense than water and help provide static lift.

What are limitations of lipid-based buoyancy?

Inflexible for short-term adjustment, bulky, increases drag.

What is the main advantage of gas-based buoyancy?

It allows rapid and tunable buoyancy changes using small amounts of gas.

What are the downsides of gas-based systems?

Gases are compressible and influenced by depth (Boyle’s Law), requiring regulation.

What is static lift?

Lift provided by buoyant structures like lipids or gas bladders; energetically efficient but slow to adjust.

What is dynamic lift?

Lift generated by movement through water using fins; requires constant swimming.

Which fish types use static vs. dynamic lift?

Static: slow swimmers (e.g., basking sharks); Dynamic: fast predators (e.g., tuna).

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How do sharks use lift?

Symmetrical tails and pectoral fins generate hydrodynamic lift; some use lipid-rich livers for static lift.

How much pressure increases per 10 meters of depth?

Pressure increases by 1 atmosphere (atm) every 10 meters.

What does Boyle’s Law state?

Pressure and volume are inversely proportional — P↑ = V↓.

How does Boyle’s Law affect swim bladders at depth?

Pressure compresses gas volume, decreasing buoyancy; fish must add gas to maintain lift.

What are physostomous fish?

Fish with a pneumatic duct connecting swim bladder to gut; can gulp/release air at the surface.

What are physoclistous fish?

Fish with a closed swim bladder; use gas glands to regulate internal gas via bloodstream.

What is the gas gland and its function?

Secretes lactic acid to trigger oxygen release from hemoglobin into swim bladder.

What is the Root effect?

Reduces hemoglobin’s oxygen-carrying capacity at low pH, enhancing oxygen release.

What is the Bohr effect?

Decreases hemoglobin’s affinity for oxygen in low pH environments.

What is the salting-out effect?

High solute concentration from lactic acid reduces oxygen solubility, promoting diffusion.

What is the rete mirabile?

Countercurrent system maintaining high oxygen partial pressure to allow gas diffusion into bladder.

Why do deep-sea fish have long rete mirabile?

To maintain pressure gradients for gas exchange under extreme depths.

How do fish expel gas from the swim bladder?

Via blood flow control, ovals, sphincter muscles, and guanine crystals reducing permeability.

Why don’t rapid swimmers like tuna have swim bladders?

They rely on dynamic lift and lipids to change depth quickly without barotrauma.

What adaptations do benthic/flatfish have for buoyancy?

Dense bodies, reduced/absent swim bladders, flattened shapes.

What is the function of swim bladders in sonar detection?

Swim bladders reflect sonar strongly due to density differences, creating detectable layers.

What’s the significance of buoyancy for fish ecology?

Influences locomotion, habitat use, foraging style, energy efficiency, and predator avoidance.