Fish physiology Horst Kaiser Ichthyology II, 2012 2
Fish physiology Horst Kaiser Ichthyology II, 2012 2 Respiration 3 Life in water (1/2) Water is 840 times more dense and 60 times more viscous than air. Oxygen: Air: 210 ml/L O2 at 21% partial pressure Water: up 15 mg/L O2 (dep. on temperature) Sea water holds 18% less O2 than freshwater Oxygen consumption in fish 17 mg/kg/h @10C 100-500 mg/kg/h @ 30C
More than 40 genera of fishes breath oxygen using other methods than their gills. 4 Life in water (2/2) Energy demand to accomplish respiration: approx. 50% of total demand but can be up to 90% Blood volume: 2-4 mL / 100 g; (nucleated RBC) Gill surface area: 150300 mm2 / g tissue
Systolic blood pressure: about 44 mm Hg Gill irrigation: 5-20 L H2O / kg BM / h Opercular beat counts: 40-60 / minute 5 Henrys law VO2 = PO2 VO2 = O2 concentration in ml/L (or mg/L) = solubility coefficient: the volume of O2 dissolved in water: ml O2/L/atm PO2 = PO2 partial pressure (atm) 6 Metabolism of trout vs turtle Trout Oxygen requirement Turtle
~ 5 ml / min / kg ~ 5 ml / min / kg Ventilation volume 600 ml H2O / min / kg 50 ml air / min / kg Routine costs for ventilation 10 % 2% ref. D Water flow
Blood flow Water flow Blood flow Water flow 8 Gills and kidney: Osmoregulatory organs 9 PAIRED HOLOBRANCHS tongue Gill rakers Four paired holobranchs
10 11 12 Countercurrent exchange The difference in oxygen partial pressure PO2 between water and plasma strongly influences the uptake of oxygen at the gill lamella / water interface! Decreasing oxygen level Increasing oxygen level Water interface at the lamella 13
Data are from John Radulls thesis Oxygen consumption in grunter b Model: R=a*W R=0.67*W -.042 0.7 0.6 mg O2/g/h 0.5 0.4 0.3
0.2 0.1 0.0 0 2 4 6 8 Weight (g/fish) 10 12
14 16 18 Data are from John Radulls thesis Possible explanations for metabolic rate changes with size Developmental changes of relative weights of different organs Liver and gills weigh relatively less Swimming musculature becomes more developed Metabolic intensities of different tissues may decline with increasing size (age) Differences between species Possible effect of test temperature Possible interactions between temperature and species Salinity?
Metabolic rate in fish Standard metabolic rate (SMR) Routine metabolic rate (RMR) Active metabolic rate (AMR) Metabolic scope (MS): MS = SMR AMR 21 -1 .h ) 0.80
20:00 0:00 Hour of day 4:00 8:00 ref. F 22 Intermittent respirometry MS Mechanical stirrer POS Oxygen probe
Syringe IS Water flow Glass flask Water flow ref. G 23 Intermittent respirometry and its applications Some research examples and applications Oxygen consumption (mg g
-1 h-1) The effect of handling stress on metabolic rate changes in spotted grunter 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 50
100 150 200 250 Time after stress application (m in) 25 Ref.: Radull et al. 2000 0.8 0.6 0.4 0.2 Oxygen consumption (mg g
1 -1 -1 h ) 1.2 0 8 6 4 2
0 -1 Dissolved oxygen concentration (mg L ) ref. F 26 Lets design an intermittent respirometer: Basic data for a small fish species Oxygen consumption: 500 mg O2 / kg / hour Fish biomass: 12 g (we will use 1 fish) Oxygen consumption per fish: ? mg O2 / hour O2 at start of measurement: 9 mg / L O2 Critical lower limit: 6 mg / L O2 How many minutes should one measurement take assuming the volume of the respirometer is 1000
mL (1 Liter)? 27 Lets design an intermittent respirometer: Basic data for a small fish species Oxygen consumption: 500 mg O2 / kg / hour Fish biomass: 12 g Oxygen consumption: ? mg O2 / hour 500 mg O2 / (1000 g / 12 g) / hour = 6 mg / hour O2 at start of measurement: 9 mg / L O2 Critical lower limit: 6 mg / L O2 Consumption: 9 6 mg = 3 mg O2 How many minutes should one measurement take? 3 mg O2 / (6 mg O2 / hour) = 0.5 hours = 30 minutes 28 Respiration
Ventilation CO2 is transported to gills and excreted O2 diffusion Once O2 has been offloaded CO2 diffuses into the RBC O2 dissolves into plasma
O2 diffuses across capillary walls & cytoplasm to mitochondria O2 binds to haemoglobin in RBCs 29 Osmoregulation Nitrogenexcretion Acid-base balance
Respiration 30 Hemoglobin (Hb) Fish have nucleated red blood cells! Some species have more than 1 type of Hb Each protein molecule has 4 globin subunits each with one haem group to bind O2 Hb exists in 2 states, a tense (T) state with low affinity to O2, and a relaxed state (R) with high affinity. A shift from T -> R increases O2 binding capacity The four units cooperate to increase O2-uptake What changes the state from T to R? 31 Carbon dioxide transport the chemistry of CO2 in water
CO2 + H2O H2CO3 HCO3- + H+ Carbon dioxide Carbonic acid Bicarbonate ion 32 Carbonic anhydrase speeds up carbon dioxide dissociation in the cell Extracellular CO2 + H2O Slow reaction
H2CO3 Carbonic anhydrase CO2 + H2O HCO3- + H+ Fast reaction H2CO3 HCO3- + H+ Red blood cell 33 Carbonic anhydrase speeds up carbon dioxide dissociation at the tissues
Carbonic anhydrase CO2 + H2O HCO3- transport to plasma in exchange for ClFast reaction H2CO3 HCO3- + H+ Drop in pH ! Hemoglobin changes state and releases O2 O2 diffuse to plasma and tissues 34 Carbonic anhydrase speeds up carbon dioxide
dissociation at the gills Carbonic anhydrase HCO3- + H+ HCO3- transport to blood cell in exchange for Cl- Fast reaction H2CO3 CO2 diffusion to plasma and water CO2 + H2O Release of CO2 increases pH Hemoglobin changes state and is
ready to pick up O2 at the gills. 35 Percent saturation of Hb with O2 Bohr effect higher pH (gills) Exponential increase due to Hb subunit cooperation lower pH (tissues) Dissociation
curves parallel Partial pressure of oxygen (PO2) Reduced affinity under acidic conditions ref. B Bohr effect species differences Percent saturation of Hb with O2 Sessile species with high Hb-affinity to oxygen Can cope with low-oxygen conditions Active species with low Hb-affinity to oxygen Requires high oxygen levels to survive. Partial pressure of oxygen (PO2)
Reduced affinity under acidic conditions ref. B CO2 Gill interface O2 CO2 pH pH Increased Bohr and root effect O2 CO2
Blood stream O2 to organs Hypercapnia Excess CO2 through respiration, and in water Reduced opercular movement -> impaired CO2 excretion Hyperlacticaemia Drop in blood pH (lactic acid, stress, excessive swimming)
38 Why is the Root effect unique to fish? Oxygen supply to the retina Gas bladder function 39 Release of gas from the gas bladder Physostomous fishes Pneumatic duct to the gut in most but not all species Physoclistous fishes Closed gas bladder Release gas into the blood (specialised oval area) Excess gas is carried to the gills 40
The rete counter-current system Eye Gas bladder ref. B Example: gas bladder rete in eel Cross section: 5 mm2 Volume: 21 mm3 Surface area: 30 cm2 Capillaries: 20.000 to 40.000 Artery diameter: 9 - 10 m Venous capillary: 11 13 m Diffusion distance (capillaries): 1 m Capillary length: 4 mm Holes in capillary: 20 80 nm Hole diaphragm: 5 nm
41 Pre-rete Arterie Rete mirabile: Changes of gas content, pH and lactate in the capillaries PCO2 / PO2 pH Lactate PCO2 / PO2 pH Lactate Post-rete Arterie Gas gland epithelium O2
Rete mirabile CO2 PCO2 / PO2 pH Lactate PCO2 / PO2 pH Lactate Bladder caps Pre-rete Vein Post-rete Vein Three processes: Bohr / Root shift Salting out
Counter-current diffusion Secretory bladder ref. D 42 Percent saturation of Hb with O2 Root effect O2 Saturation is not reached even if sufficient O2 available! higher pH (gills) Subunit cooperation
Some subunits fail to load O2 much lower pH (retina / swimbladder) Partial pressure of oxygen (PO2) Decreased capacity under acidic conditions 43
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