Lecture 6: Buoyancy & Locomotion

• What is the advantage of neutral buoyancy?


  It saves energy that may be used in controlling depth and position
• What are the 4 strategies of controlling buoyancy?

  Low-Density Compounds

  Generating Lift with Fins

  Reducing Heavy Tissues

  Gas Filled Spaces
• What is the lipid sharks and some bony fish use to control their buoyancy?

  Squalene
• What are some other fish that control their buoyancy with low-density compounds?

  Sablefish

  Rockfish

  Medusadish

  Cusk Eels
• How does a shark or bony fish generate lift?

  Heterocercal tail and pectoral fins balancing against the weight of their skull
• Bernoulli's Principle: An increase in velocity of a fluid causes a decrease in pressure
• What fish reduce heavy tissues to control their buoyancy?

  Sharks

  Deep Sea Fish
• Why might an organism reduce heavy tissues to control buoyancy?


  Food is Scarce

  Lipids and Swim Bladders Cost Energy

  Cartilage allows buoyancy, migration, & large size
• Paddlefishes and Sturgeons are large, highly migratory freshwater fishes with derived cartilaginous skeletons
• What is different about a swim bladder compared to other strategies for controlling buoyancy?

  It allows precise control
• What type of fish have swim bladders?

  Bony Fish
• Why do salt water dwelling fish have smaller swim bladders?

  Salt increases buoyancy
• What type of fish has a larger swim bladder: salt water or fresh water?

  Fresh Water
• Physostomus Swim Bladder: The more primative of swim bladder types, this bladder is connected to the gut via the pneumatic duct and inflates by gulping air at the surface
• What is the physostomus swim bladder connected to the gut by?

  Pneumatic duct
• How does the physostomus swim bladder inflate?

  Gulping air
• What are some examples of fish that use physostomus swim bladders?

  Herring

  Salmon

  Minnows

  Eels

  Catfish
• Physoclistous Swim Bladder: The more evolved form of a swim bladder, this organ is connected to the circulatory system and inflates through the use of the rete mirabile and gas gland.
• How does the physoclistous swim bladder inflate?

  It is connected to the circulatory system
• What organs are used to inflate the swim bladder?

  Rete mirabile

  Gas Gland
• What swim bladder is the more evolved version?

  Physoclistous
• What swim bladder is the lesser evolved version?

  Physostomus
• In what lineage did the physoclistous swim bladder first evolve?

  Neoteleostei
• Where are species with physostomus swim bladders found?

  Near the surface
• Why can't species with a physostomus swim bladder achieve neutral buoyancy at depth?

  The amount of gas needed would be so great that they could not submerge.
• How does the physoclistous swim bladder work?

  The gas gland excretes lactic acid and produces CO2 creating an acidic environment so hemoglobin will lose its oxygen and it will diffuse into the swim bladder
• What is the difference between a deep-water fish and a shallow-water fish's buoyancy counter current exchange system?

  A deep water fish has a longer exchange system
• How does the buoyancy counter current exchange system work?

  Blood flowing back to the body first enters a rete

  All excess carbon dioxide and oxygen produced in the gas gland diffuses back to the arteries

  The gas gland is supplied
• How does the physoclistous swim bladder deflate?

  Diffusing gas back into blood at vascular ovale
• What does a teleost lacking a swim bladder say about its habitat?

  It is likely benthic, pelagic, or deep water dwelling
• Drag: The removal of momentum of a moving body through a fluid
• Thrust: Force in the animals' direction of movement and made by the movement of fins
• Drag is affected by the ration of inertial forces to viscous forces
• Inertial forces: Inertia; the force that keeps things moving.
• Viscous Forces: Forces that make objects slow or stop.
• Reynolds Number: The ratio between inertia and viscosity
• Drag and Renolds are inversely proportional
• What does a low Renolds Number mean?

  Fluid is more viscous

  Easier to start moving but needs constant exertion

  Home to smaller fish

  Fish at this RE start move and stop when they reach the RE
• What does a high Renolds Number mean?

  Fluid is less viscous

  It takes more energy to start moving but less energy thereafter

  Continual movement is possible

  Larger organisms are in this environment
• What are the three ways fish reduce drag?

  Body shape

  Scale type

  Mucous