Lecture #9

Question 1

What is the Davenport diagram and why it is useful?

Answer 1

-describes Acid-Base status in biological systems (blood, cells, etc)
A-B status: pCO2, pH and [HCO3-]
-for an air-breathing animal, the range of pCO2 and [HCO3-] values is relatively high, and the range of pH values is relatively low

Question 2

What are the four essential components of the Davenport diagram?

Answer 2

• Non-bicarbonate buffering (NBB) line
• top (isopleths)= PCO2 (notice it goes from high to low)
• Y-axis= [HCO3-]
• X-axis= pH

Question 3

Which fish will have a higher non-bicarbonate buffering (NBB) capacity in its white muscle, a blue fin tuna or a flounder? Why?

Answer 3

• blue fin tuna

- does more anaerobic respiration and needs to buffer the acid in its blood more

Question 4

The hemolymph of squid can carry 5 ml O2 / 100 mL, and the hemolymph of octopus can carry 1 mL O2 / 100 mL. Which animal do you think will have a higher hemolymph NBB capacity, and why?

Answer 4

• the octopus
• the organism that can carry less oxygen is likely doing anaerobic respiration more
• this indicates a greater need to buffer their hemolymph and a higher NBB capacity (steeper slope)

Question 5

Describe the three most common types of blood A/B stress experienced by aquatic animals, and how they compensate them

Answer 5

• Respiratory acidosis: caused by elevated pCO2 (e.g. hypercapnia)
• -gills secrete H+ and retain HCO3-
• -pH is compensated
• -CO2 remains elevated
• Metabolic acidosis: caused by addition of H+ (e.g. anaerobic metabolism)
• -Gills excrete H+ and retain HCO3-
• -Restores pH
• -Everything goes back to normal
• Metabolic alkalosis: caused by addition of HCO3- (e.g. post-feeding)
• -Gills excrete HCO3- and retain H+
• -Restores pH
• -Everything goes back to normal

Question 6

How will the Davenport diagram would look like for the painted turtle and the Crucian carp during the winter?

Answer 6

• painted turtle breathes air while crucian carp does not, so numbers on axes are much larger
• painted turtle has steeper slope

Question 7

Draw Davenport diagrams for a high performance fish (e.g. a tuna) after 5 and 10 minutes of very intense swimming while it chases a prey. What type of acid-base disturbance took place? How does the tuna compensate?

Answer 7

• metabolic acidosis
• 10 minutes of intense swimming will result in a greater change from the origin
• Gills excrete H+ and retain HCO3- to compensate

Question 8

Now let’s consider two different aquaculture facilities. One holds 20 seabass, and the other holds 40. Draw the Davenport diagram for one seabass from each facility.

Answer 8

The facility with 40 seabass will have a greater reduction of pH along the NBB line. The compensated final position will be at the same pH for the two, but it will be at a higher HCO3- for the tank with more fish because of the greater amount of compensation.

Question 9

Draw two Davenport diagrams, one for a shark after eating a 1 kg fish, and another for the same shark after eating a 2 kg fish (~2 and 4 pounds, respectively). What type of acid-base disturbance took place? How does the shark compensate?

Answer 9

• metabolic alkalosis
• the larger fish will cause a greater increase in HCO3- concentration
• the gills will excrete HCO3- and retain H+ to rebalance the pH

Question 10

How do you think the python will compensate blood alkalosis after a large meal? (e.g. after eating a deer)

Answer 10

• the kidneys could secrete HCO3- to restore the pH
• the lungs could hypoventilate and accumulate CO2 to compensate the pH but the HCO3- concentration would still be higher than before and slightly increased from the extra CO2