Physiology of Fishes Flashcards
What are the two main physiological challenges for fish?
Extracting oxygen and excreting CO₂ efficiently while maintaining energy balance.
Why is oxygen availability a limiting factor for fish?
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.
Why is water a challenging medium for gas exchange compared to air?
Water is 800 times denser and more viscous, requiring more metabolic energy to ventilate gills.
How efficient are fish gills at extracting dissolved oxygen?
Fish gills achieve 75–90% oxygen extraction efficiency, compared to mammalian lungs at 10–15%.
What is the role of counter-current flow in gill function?
It maximizes oxygen extraction by ensuring blood encounters water with higher oxygen concentration.
What additional functions do gills perform besides gas exchange?
Excretion (ammonia), osmoregulation, and acid-base balance.
What is ram ventilation, and which fishes use it?
Ram ventilation is unidirectional water flow created by swimming, used by fast-moving species like tuna.
Why do metabolically active fish require larger gill surface areas?
Larger gill surface areas increase oxygen extraction efficiency to meet higher energy demands.
How is oxygen transported in fish blood?
Oxygen binds to hemoglobin in red blood cells and is released in tissues.
What is the Bohr effect?
Increased CO₂ and acidity reduce hemoglobin’s oxygen-binding ability, facilitating oxygen release in tissues.
What happens to CO₂ in fish tissues?
CO₂ reacts with water to form carbonic acid, which dissociates into bicarbonate ions (HCO₃⁻) and protons (H⁺), lowering pH and stimulating oxygen release.
What is metabolic rate, and how is it measured in fish?
Metabolic rate is the energy consumption rate, often estimated via oxygen consumption in respirometry chambers.
How does body size affect metabolic rate?
Larger fish have higher absolute metabolic rates but lower mass-specific metabolic rates compared to smaller fish.
What is Kleiber’s Law?
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.
What is the Q₁₀ value?
It describes how metabolic reaction rates increase with a 10°C temperature rise.
How do body size and temperature affect fish metabolism?
Bigger fish and fish in warmer waters need more oxygen; however, warm water holds less dissolved oxygen, compounding the challenge.
What are the five types of metabolic rates?
- 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.
Why is FMR considered ecologically relevant?
It integrates active and inactive periods, reflecting energy use in natural settings.
What is aerobic scope, and why is it important?
The difference between SMR and MMR, representing energy available for growth, reproduction, and behavior.
How does temperature affect aerobic scope?
Aerobic scope peaks at an optimal temperature and declines as SMR and MMR converge due to oxygen supply limitations.
What are the implications of aerobic scope theory for fish in a warming world?
Rising temperatures reduce oxygen supply, limiting body size and habitat distribution, particularly in tropical regions.
How might climate change impact global fisheries?
Warming oceans and reduced oxygen availability could shrink fish body sizes and decrease fishery potential, especially in tropical regions.
What is the ‘shrinking fish’ model?
A theory suggesting fish maximum size is limited by the oxygen supply/demand ratio, which worsens with rising temperatures.
Why do small fish not always flee predators in the ocean?
In water, building oxygen debt or CO₂ excess during sustained activity is costly, making fleeing risky for both prey and predators.
