Fish Physiology Flashcards
Removing oxygen from water challenge
Concentrations typically 1-10 ml/L
Water is 800x denser than air, so requires more energy to force water across gills.
Active ventilation can comprise between 0.5% and 45% of total metabolic demand of fish.
Gills
Fish gills show 75-90% efficiency, mammalian lung is 10-15%
Main site of carbon dioxide and nitrogen waste release
Gills function in GE, excretion, osmoregulation and acid-base balance
Counter current flow
Maximises oxygen extraction by ensuring blood is always associated with water with higher oxygen concentrations.
Ram ventilation
highly active fast fishes can use motion to create a unidirectional flow.
As water is forced between the gills, P increases, meaning it must keep moving
Ram ventilation becomes more efficient over 0.3m/s
Gill SA
Gills are metabolically costly so there is selective P to reduce gill SA
However, metabolically active lifestyles require more oxygen efficiency
SA is under active selection with higher gill surface area co varying with greater energetic demand
Bohr Effect
If there is lots of carbon dioxide (HCO3 and H) structure of Hb is altered so that O is less tightly bound.
If carbon dioxide is low, Hb altered to reverse.
1. O extracted at the gills is transported loosely bound to erythrocytes
2. carbon dioxide formed in tissues from respiration is transported as bicarbonate ion.
3. bicarbonate is synthesised in erythrocytes by carbonic anhydrase, and releases a proton, increase acid and release oxygen
4. carbon dioxide is released from bicarbonate at the ion exchange surface, catalysted by CA. Process consumes proton and reduces acidity.
Bohr effect on tissues
In tissues there is a high external carbon dioxide concentration. CO2 diffuses into the redblood cell and dissociates to HCO3 and H+, decreasing pH. Results in release of oxygen which diffuses to the tissues
Bohr effect on gills
External carbon dioxide is concentration is low and O is high, Bicarbonate ion and proton combine to produce carbon dioxide which diffuses out the cell. Raises inter-cellular pH and promotes binding of O to Hb.
Fish can’t pant
Can’t increase rate of flow of water over the gills to increase rates of carbon dioxide loss.
Alternative is to reduce oxygen demand.
So fish don’t flee
Fish don’t eat too much
Metabolism of food produces carbon dioxide, metabolically costly to remove.
Fish can be limited in how much prey they can consume by the amount of oxygen it costs them to process the food.
Metabolism
Respiration in heterotrophics:
* C6H12O6 + 6O2 = 6CO2 + 6H2O + ATP
Combustion of reduced organic compounds releases energy to drive other reactions, captured as ATP and carbon dioxide as a by product.
Rate at which energy is used is metabolic rate
Measured by the heat produced by animal. Measured in joules. However relatively difficult to take, often measure oxygen consumption as a proxy.
Metabolism and body size
Bigger animals have more cells and higher metabolic rate
Number of cells roughly doubles but when weight doubles metabolic rate increases 75%
Mass-specific metabolic rate falls with increasing body size
Metabolic rate = metabolic level x mass^0.75
Metabolism and temperature
Metabolic reactions are endothermic reactions, more heat energy that is supplied the faster they run.
Thermal sensitivity = Q10
Metabolic theory
B = BoM^~e^-E/kT
B = metabolic rate
Bo = scaling
M = mass
~ = 0.75
k = boltzman
T = temperature
Aerobic scope
Space between maximum metabolic rate and standard metabolic rate with increasing temperaute is the amount of metabolic energy that is available for all behaviour or aerobic scope.
Theory suggests that MMR will increase with temp faster than SMR until metabolic rate is limited by the rate at which oxygen can be delivered to the body.
Produces a divergence in thermal sensitivity of SMR and MMR, so aerobic scope also varies with temperature.
Temperature at which aerobic scope is maximised, in theory is an optimum, and a powerful idea in potential consequence of climate warming.
