October 6, Lecture 14. Gills & Respiration. 1. Why do fish need O2? Why do fish have gills? Why don’t they rely on diffusion across their bodies? 2. Respiratory demands in an aquatic environment 3. How gills work 4. Respiration other than gills 5. Counter current exchange system. 6. Active vs. sluggish fish

Creatures such as bacteria and protists living in aquatic environments rely on diffusion of O2 for respiration. Why do fish need gills?

1. The Physical Nature of Water Component% Oxygen20.95 Carbon Dioxide0.03 Nitrogen78.09 Argon0.93 Total100 Composition of Dry Atmospheric Air

1. The Physical Nature of Water ComponentSolubility (ml gas/liter freshwater) Oxygen34.1 Carbon Dioxide1,019.0 Nitrogen16.9 Solubility of gases at 15C at 1 atmosphere pressure

Hagfish Lamprey Hagfish & Lamprey gill pouches - Main point is that they don’t have gill arches & gill filaments. They have gill pouches.

Shark gill Bony fish gill Gnathostomata have gill arches and gill filaments.

sharkteleost gill arch gill raker Main points: 2 gill filaments for each gill arch; sharks have a gill septum which reduces water flow

gill filaments gill lamellae

Water flow through gill of teleost

Main point is that the direction of blood flow is opposite the direction of water flow.

Gill surface area goes up with activity level

Lamellae thickness goes down with activity level.

Summary Questions 1. Why do fish have gills? Why don’t they rely on diffusion across their bodies? 2. Why is respiration in an aquatic environment difficult? 3. How do gills work? Explain the design of the gills including the gill arch, gill filaments, and lamellae. What is the site of O2 absorption and CO2 release? 4. In what types of environments do you expect to see fish capable of respiration using structures other than gills? 5. Explain the significance of the counter current exchange system. 6. How do gills differ between fish that swim very fast versus those that are sluggish? 7. Despite the fact that O2 has slightly lower solubility in saltwater than in freshwater, most of the airbreathers are freshwater species. Why do you think this is? 8. Explain the effects of temperature and solute concentration on O2 solubility. 9. Table 5.1 in your book lists a variety of respiratory organs other than gills. Describe how the following structures work as respiratory organs and list 2 taxa that have them: lungs, gas bladder, skin, stomach/intestine, opercular chamber, suprabranchial labyrinth organ.