Buoyancy

What was the Archimedes Principle?

Buoyancy

Buoyancy

Force exerted by a liquid, gas or other fluid, that opposes an objects weight

Were placoderms negatively or positively buoyant?

Negatively buoyant

-Bottom dwellers

-Contained heavy armour

What does a reduction in submerged weight allowed fish to?

-Exploit the midwater region

-Reduce the cost of transport

How was the reductions in submerged fish achieved?

-Reduction of heavy, dense body parts

-Buoyancy aids

What are the 2 ways to counteract lift?

-Dynamic lift (Active)

-Static lift (Buoyancy/Passive)

Is dynamic lift positive or negative in sharks?

Negative

Equation for dynamic lift in sharks?

W=B+C

W→ Submerged weight of fish

B→ Hydrodynamic lift from pectoral fins

C→ Lift from caudal fin

What happens if W=B+C and if W>B+C?

W=B+C

-Neutral buoyancy

W>B+C

-Negative buoyancy (Sink)

What does the paper “Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure“ show?

Volumetric imaging to analyse shark tail hydrodynamics, revealing a three-dimensional dual-ring vortex wake structure that enhances propulsion efficiency

Key points of “Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure“

Objective:

-Investigate the hydrodynamics of shark tail movement using volumetric imaging techniques.

Methodology:

-Used three-dimensional imaging to analyze water flow patterns generated by shark tails.

Findings:

-Identified a dual-ring vortex wake structure, different from traditional single-ring vortex wakes seen in other aquatic animals.

Significance:

-Suggests that sharks use a unique propulsion mechanism, enhancing efficiency and manoeuvrability.

Implications:

-Provides insights into shark locomotion and informs biomimetic designs for underwater robotics.

Citate “Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure“

Flammang et al., 2011

What are the advantages of static lift from lipids?

Lipids are incompressible

-Buoyancy not affected by depth

What are the disadvantages of static lift involving lipids?

Lipids only slightly less dense than water

-So need large amount of lipids

Quantity of lipid cannot be adjusted quickly

-No ability to compensate for short term changes

Where do elasmobranchs store lipids?

Liver

-Liver can exceed 20% of body weight

How much does teleost liver make up their bodyweight?

1-2%

What lift is more economical at high speed and actively seeking prey?

Dynamic lift

What lift is more economical at low speed and opportunistic prey ecounters?

Static lift

Which 2 bladders can be used for gas buoyancy (Static lift)?

Swim or Gas bladder

Advantages of using gas as buoyancy aid?

-Gas is less dense than lipid

-Quantity of gas can be adjusted quickly to compensate for short term changes

Disadvantages of using gas as a buoyancy aid?

Boyles Law

Boyles Law

At a constant temp the volume of a gas varies inversely with pressure

What happens if the fish swim descents and ascents?

Descent

-Swim bladder compresses (Negatively buoyant)

-To maintain neutral buoyancy more gas into the gas bladder

Ascent

-Swim bladder will expand (Positively buoyant)

-To maintain neutral buoyancy more gas needs to be expelled from gas bladder

2 type of gasbladders

Physostomatous and Physoclistous

Physostomatous

Pneumatic duct between swim bladder and gut open throughout life

-Lower teleosts (Clupeids, Anguilla)

Physoclistous

Pneumatic duct closes early in development

-Advanced teleosts

How to physostome get gas into the bladder?

-Simply shallow gas at the surface

-Some species have a special organ to inflate bladder (Gas Gland)

→Anguillids

How to physostome release gas to prevent descent with massive positive buoyancy?

Burp it out

How to physoclist get gas into their bladders?

Gas gland that inflate the bladder

-Uses passive diffusion to get oxygen into gas bladder lumen

-Relies on differential partial pressure

How does gas gland maintain diffusion rate?

Rete mirabile

Rete mirabile

Counter current exchange system with large numbers of arterial and venous capillaries running counter to and in very close proximity to one another

How does rete mirabile work?

-Blood enters gas gland

with oxygen primarily bound to haemoglobin (hb)

-O2 needs to disassociate from hb and go into solution

-Increase in pp leads to passive diffusion

What is the mechanism of rete mirabile?

Cells surrounding the gas gland are rich in glycogen, secreting lactic acid (anaerobic metabolism)

What are the implications of increased acidity in the gas gland?

Bohr effect

-A reduction of O2-Hb affinity

Root effect

-A reduction in the O2 carrying capacity of Hb

Salting out effect

-Increase in ionic content of blood reduces carrying capacity of all gases

Dissociation of carbon dioxide from bicarbonates

-CO2 reacts with Hb and plasma proteins to produce Carbamino compounds, further reduce O2-Hb affinity

How does a fish increase the O2 multiplication at depth?

Having a longer rete mirabile

-Bassozetus taenia has a rete mirabile of 25 mm and lives at a depth of 5000m

How do physoclistous retain gas in the bladder?

-Wall of SB had cells containing sheets of guanine crystals reducing permeability 1000-fold

-Restrict access of O2 in swim bladder to blood supply

Adaptations of physoclistous for vertical movement?

-Large oval for size of swim bladder

-Large blood vessels supplying oval

-Diffusion distance between swim bladder and capillaries <1μm

-Lose swim bladder altogether

Examples of fish with no swimbladder?

Scombrids

-Allow rapid vertical movement o evade predators and capture prey

-Avoid detection by toothed whales

What are the adaptations for buoyancy in deep-sea fish?

-Larger oval per volume of swim bladder

-Lightly ossified skeleton

-Few, if any scales

-Reduced musculature (important if weak bones)