Physiology of Fishes

Question 1

What are the two main physiological challenges for fish?

Answer 1

Extracting oxygen and excreting CO₂ efficiently while maintaining energy balance.

Question 2

Why is oxygen availability a limiting factor for fish?

Answer 2

Water contains only 1–10 ml/L dissolved oxygen, less than 5% of the oxygen concentration in air, making energy-demanding activities harder to sustain.

Question 3

Why is water a challenging medium for gas exchange compared to air?

Answer 3

Water is 800 times denser and more viscous, requiring more metabolic energy to ventilate gills.

Question 4

How efficient are fish gills at extracting dissolved oxygen?

Answer 4

Fish gills achieve 75–90% oxygen extraction efficiency, compared to mammalian lungs at 10–15%.

Question 5

What is the role of counter-current flow in gill function?

Answer 5

It maximizes oxygen extraction by ensuring blood encounters water with higher oxygen concentration.

Question 6

What additional functions do gills perform besides gas exchange?

Answer 6

Excretion (ammonia), osmoregulation, and acid-base balance.

Question 7

What is ram ventilation, and which fishes use it?

Answer 7

Ram ventilation is unidirectional water flow created by swimming, used by fast-moving species like tuna.

Question 8

Why do metabolically active fish require larger gill surface areas?

Answer 8

Larger gill surface areas increase oxygen extraction efficiency to meet higher energy demands.

Question 9

How is oxygen transported in fish blood?

Answer 9

Oxygen binds to hemoglobin in red blood cells and is released in tissues.

Question 10

What is the Bohr effect?

Answer 10

Increased CO₂ and acidity reduce hemoglobin’s oxygen-binding ability, facilitating oxygen release in tissues.

Question 11

What happens to CO₂ in fish tissues?

Answer 11

CO₂ reacts with water to form carbonic acid, which dissociates into bicarbonate ions (HCO₃⁻) and protons (H⁺), lowering pH and stimulating oxygen release.

Question 12

What is metabolic rate, and how is it measured in fish?

Answer 12

Metabolic rate is the energy consumption rate, often estimated via oxygen consumption in respirometry chambers.

Question 13

How does body size affect metabolic rate?

Answer 13

Larger fish have higher absolute metabolic rates but lower mass-specific metabolic rates compared to smaller fish.

Question 14

What is Kleiber’s Law?

Answer 14

Metabolic rate scales with body size at a slope less than 1 (approximately 0.75), meaning metabolic rate increases less than proportionally with body size.

Question 15

What is the Q₁₀ value?

Answer 15

It describes how metabolic reaction rates increase with a 10°C temperature rise.

Question 16

How do body size and temperature affect fish metabolism?

Answer 16

Bigger fish and fish in warmer waters need more oxygen; however, warm water holds less dissolved oxygen, compounding the challenge.

Question 17

What are the five types of metabolic rates?

Answer 17

• Basal Metabolic Rate (BMR): Maintenance energy cost, not relevant for most fish.
• Standard Metabolic Rate (SMR): Maintenance cost in resting conditions.
• Routine Metabolic Rate (RMR): Energy cost of routine activity.
• Maximum Metabolic Rate (MMR): Maximum energy expenditure during activity.
• Field Metabolic Rate (FMR): Average energy cost in a natural environment.

Question 18

Why is FMR considered ecologically relevant?

Answer 18

It integrates active and inactive periods, reflecting energy use in natural settings.

Question 19

What is aerobic scope, and why is it important?

Answer 19

The difference between SMR and MMR, representing energy available for growth, reproduction, and behavior.

Question 20

How does temperature affect aerobic scope?

Answer 20

Aerobic scope peaks at an optimal temperature and declines as SMR and MMR converge due to oxygen supply limitations.

Question 21

What are the implications of aerobic scope theory for fish in a warming world?

Answer 21

Rising temperatures reduce oxygen supply, limiting body size and habitat distribution, particularly in tropical regions.

Question 22

How might climate change impact global fisheries?

Answer 22

Warming oceans and reduced oxygen availability could shrink fish body sizes and decrease fishery potential, especially in tropical regions.

Question 23

What is the ‘shrinking fish’ model?

Answer 23

A theory suggesting fish maximum size is limited by the oxygen supply/demand ratio, which worsens with rising temperatures.

Question 24

Why do small fish not always flee predators in the ocean?

Answer 24

In water, building oxygen debt or CO₂ excess during sustained activity is costly, making fleeing risky for both prey and predators.

Question 25

How does feeding relate to oxygen availability in fish?

Answer 25

Metabolizing food produces CO₂, increasing acidity and oxygen demand, which may limit prey consumption.

Question 26

What key physiological challenges influence fish diversity?

Answer 26

Efficient oxygen extraction, energy management, and adaptation to environmental constraints shape fish morphology, behavior, and habitat.

Question 27

Why do aquatic predator-prey interactions differ from terrestrial ones?

Answer 27

Fleeing or chasing in water is energetically costly; excessive oxygen debt or CO₂ build-up can incapacitate predators or prey.

Question 28

What specific features make fish gills highly efficient?

Answer 28

Lamellae maximize surface area, and counter-current flow ensures blood always contacts water with higher oxygen concentration.

Question 29

How does carbonic anhydrase (CA) influence CO₂ excretion in fish?

Answer 29

CA catalyzes the conversion of CO₂ into bicarbonate (HCO₃⁻) and protons (H⁺), lowering pH and facilitating oxygen release.

Question 30

Why is the Bohr effect particularly significant for fish?

Answer 30

Fish face unique challenges in maintaining pH balance in water, where CO₂ buildup directly affects oxygen transport.

Question 31

How does the thermal sensitivity of SMR and MMR affect aerobic scope?

Answer 31

SMR rises exponentially with temperature, while MMR peaks and declines, creating an optimal temperature for aerobic scope.

Question 32

Why do smaller animals have higher mass-specific metabolic rates?

Answer 32

Smaller animals lose heat faster and require proportionally more energy to maintain homeostasis, explaining their higher relative metabolic demand.

Question 33

How are respirometry experiments conducted for fish?

Answer 33

Fish are placed in sealed or open tanks, and the rate of oxygen removal from water is measured to estimate metabolic rate.

Question 34

What are the projected effects of climate change on fish populations?

Answer 34

Rising temperatures reduce oxygen availability, limiting body size and fishery potential, particularly in the tropics.

Question 35

What is red muscle in fishes

Answer 35

Powers fast burst swimming
High conc of myoglobin

Question 36

Why do fish swim at 1 body length per second

Answer 36

Acidity produced by resp is costly to balance
Incr rate of oxygen flow over the gills is costly
Water has low oxygen content