Heterothermy in Mackerel Sharks, Billfish, Mackerels and Swordfish

Question 1

What is the main advantage of regional endothermy in mackerel sharks, billfish and mackerels?

Answer 1

• temp of swimming muscle > water temp (Q10 warmer)

Question 2

What are 2 ecological advantages of heterothermy in mackerel sharks, billfish and mackerels?

Answer 2

• niche expansion to deeper water
• greater power output (Q10)

Question 3

What are the 4 related physiological traits of heterothermy in mackerel sharks, billfish and mackerels?

Answer 3

• higher activities for oxidative enzymes
• greater Hb P50 at muscle, lower at gill
• red muscle rich in myoglobin
• thicker vessels in rete mirabile

Question 4

What does a greater P50 at muscle mean?

Answer 4

• lower affinity for HB unloading

Question 5

What does lower P50 at gill mean?

Answer 5

• loading of O2 to Hb

Question 6

What do thicker blood vessels in rete mirabile do?

Answer 6

• minimize O2 loss to venous capillaries (greater distance for O2 to travel than in gas bladder)

Question 7

What does heterothermy cause in swordfish and billfish?

Answer 7

• constant cranial temp

Question 8

What are the 4 main features of the heater organ in swordfish and billfish?

Answer 8

• base of brain
• modified muscle fibres
• insulated by adipose tissue
• heat retention via CC exchange

Question 9

What is adipose tissue?

Answer 9

• fat

Question 10

Lamnid sharks and tunas have ____ heat exchanger only

Answer 10

• cranial

Question 11

What are the 2 main reasons constant cranial temp in swordfish and billfish is important?

Answer 11

• CNS activity unaltered by temp change
• Vision maintained at all depths (warmer eyes work better)

Question 12

What does high density of mitochondria in the heater organ do?

Answer 12

• generates heat

Question 13

What is the carotid rete and what blood does it recieve?

Answer 13

• heat exchanger (retention)
• cold blood from gill but oxygenated