Horst Kaiser
Ichthyology II, 2012
2

3

• Water is 840 times more dense and 60 times more viscous than air.
• Oxygen:
– Air: 210 ml/L O
2 at 21% partial pressure
– Water: up 15 mg/L O
2
(dep. on temperature)
– Sea water holds 18% less O
2 than freshwater
• Oxygen consumption in fish
– 17 mg/kg/h @10°C
– 100-500 mg/kg/h @ 30°C
• More than 40 genera of fishes breath oxygen using other methods than their gills.
4

• 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: 150–300 mm 2 / g tissue
• Systolic blood pressure: about 44 mm Hg
• Gill irrigation: 5-20 L H
2
O / kg BM / h
• Opercular beat counts: 40-60 / minute
5

VO
2
=
PO
2
VO
2
= O
2 concentration in
(or
)
= solubility coefficient: the volume of O
2 dissolved in water:
2
PO
2
= PO
2 partial pressure (
)
6

Trout Turtle
Oxygen requirement
Ventilation volume
Routine costs for ventilation
~ 5 ml / min / kg ~ 5 ml / min / kg
600 ml H
2
O / min / kg
50 ml air / min / kg
10 % 2 % ref. D

Water flow
Blood flow
Water flow
Water flow
Blood flow
8

Gills and kidney: Osmoregulatory organs
9

tongue
Gill rakers
Four paired holobranchs
10

11

12

Countercurrent exchange
The difference in oxygen partial pressure PO
2 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

Hagfish gill pouch
14

Oyster toadfish
Opsanus tau
Atlantic mackerel
Scomber scombrus
Horse mackerel
Trachurus trachurus
Eel, Anguilla japonica
Skipkack tuna, Katsuwonus pelamis
Angler
Lophius piscatorius

Unit gill area: mm 2 / g body mass
Patagonotothen tesselata
Gobionotothen gibberifrons
Notothenia rossi
Opsanus tau
Lophius piscatorius
Anguilla anguilla
Katsuwonus pelamis
Trachurus trachurus
Scomber scombrus
0 200 400 600 800 1000 1200 1400 1600
16

Number of gill lamellae / mm filament length
Patagonotothen tesselata
Gobionotothen gibberifrons
Notothenia rossi
Opsanus tau
Lophius piscatorius
Anguilla anguilla
Katsuwonus pelamis
Trachurus trachurus
Scomber scombrus
0 5 10 15 20 25 30 35 40 45
17

Oxygen consumption in grunter
Model: R=a*W b
R=0.56*W
0.679
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0 2 4 6 8 10 12 14 16 18
Weight (g/fish)
Data are from John Radull’s thesis

Oxygen consumption in grunter
Model: R=a*W b
R=0.67*W
-.042
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0 2 4 6 8 10 12 14 16 18
Weight (g/fish)
Data are from John Radull’s 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?

• Standard metabolic rate (SMR)
• Routine metabolic rate (RMR)
• Active metabolic rate (AMR)
• Metabolic scope (MS): MS = SMR – AMR
21

0.80
0.60
0.40
AMR
SMR
0.20
0.00
12:00 16:00 20:00 0:00
Hour of day
4:00 8:00 ref. F 22

Syringe IS
Intermittent respirometry
MS
POS
Mechanical stirrer
Oxygen probe
Water flow
Glass flask
Water flow ref. G 23

Some research examples and applications

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
Tim e after stress application (m in)
250

8 6 4 2
Dissolved oxygen concentration (mg L
-1
)
1.2
1
0.8
0.6
0
0
0.4
0.2
ref. F 26

• Basic data for a small fish species
– Oxygen consumption: 500 mg O
2
/ kg / hour
– Fish biomass: 12 g (we will use 1 fish)
– Oxygen consumption per fish: ?
mg O
2
/ hour
– O
2 at start of measurement: 9 mg / L O
2
– Critical lower limit: 6 mg / L O
2
– How many minutes should one measurement take assuming the volume of the respirometer is 1000 mL (1 Liter)?
27

• Basic data for a small fish species
– Oxygen consumption: 500 mg O
2
– Fish biomass: 12 g
/ kg / hour
– Oxygen consumption: ? mg O
2
• 500 mg O
2
/ hour
/ (1000 g / 12 g) / hour = 6 mg / hour
– O
2 at start of measurement: 9 mg / L O
– Critical lower limit: 6 mg / L O
2
• Consumption: 9 – 6 mg = 3 mg O
2
2
– How many minutes should one measurement take?
• 3 mg O
2
/ (6 mg O
2
/ hour) = 0.5 hours = 30 minutes
28

Respiration
Ventilation
CO
2 is transported to gills and excreted
O
2 diffusion
Once O
2 been has offloaded
CO
2 diffuses into the RBC
O
2 diffuses across capillary walls & cytoplasm to mitochondria
O
2 binds to haemoglobin in RBCs
O
2 dissolves into plasma
29

Nitrogenexcretion
Osmoregulation
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 O
2
• Hb exists in 2 states, a tense (T) state with low affinity to O
2 affinity.
, and a relaxed state (R) with high
• A shift from T -> R increases O
2 binding capacity
• The four units cooperate to increase O
2
• What changes the state from T to R?
-uptake
31

2
CO
2
+ H
2
O H
2
CO
3
HCO
3
+ H +
Carbon dioxide
Carbonic acid
Bicarbonate ion
32

Carbonic anhydrase speeds up carbon dioxide dissociation in the cell
Extracellular
CO
2
+ H
2
O H
Slow reaction
2
CO
3
HCO
3
+ H +
Carbonic anhydrase
Fast reaction
CO
2
+ H
2
O
Red blood cell
H
2
CO
3
HCO
3
+ H +
33

Carbonic anhydrase speeds up carbon dioxide dissociation at the tissues
Carbonic anhydrase
Fast reaction
HCO
3
transport to plasma in exchange for Cl -
CO
2
+ H
2
O H
2
CO
3
HCO
3
+ H +
Drop in pH !
Hemoglobin changes state and releases O
2
O
2 diffuse to plasma and tissues
34

Carbonic anhydrase speeds up carbon dioxide dissociation at the gills
Carbonic anhydrase
Fast reaction
CO
2 diffusion to plasma and water
HCO
3
+ H + H
2
CO
3
CO
2
+ H
2
O
HCO
3
transport to blood cell in exchange for Cl -
Release of CO
2 increases pH
Hemoglobin changes state and is ready to pick up O
2 at the gills.
35

Bohr effect
Exponential increase due to Hb subunit cooperation higher pH
(gills) lower pH
(tissues)
Dissociation curves parallel
Partial pressure of oxygen (PO
2
)
Reduced affinity under acidic conditions ref. B

Bohr effect – species differences
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 (PO
2
)
Reduced affinity under acidic conditions ref. B

Gill interface
O
2
2
2 pH
Blood stream pH O
2 to organs
Increased Bohr and root effect
O
2
2
Hypercapnia
Hyperlacticaemia
Excess CO
2 through respiration, and in water
Reduced opercular movement
-> impaired CO
2 excretion
Drop in blood pH (lactic acid, stress, excessive swimming)
38

• Oxygen supply to the retina
• Gas bladder function
39

• 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

Eye
Gas bladder
Example: gas bladder rete in eel
• Cross section: 5 mm 2
• Volume: 21 mm 3
• Surface area: 30 cm 2
• Capillaries: 20.000 to 40.000
• Artery diameter: 9 - 10 µm
• Venous capillary: 11 – 13 µm
• Diffusion distance (capillaries): 1 µm
• Capillary length: 4 mm
• Holes in capillary: 20 – 80 nm
• Hole diaphragm: 5 nm
41 ref. B

Pre-rete Arterie Rete mirabile : Changes of gas content, pH and lactate in the capillaries
PCO
2
/ PO
2 pH Lactate PCO
2
/ PO
2 pH Lactate
Rete mirabile
Post-rete Arterie
Gas gland epithelium
O
2
CO
2
Post-rete Vein
PCO
2
/ PO
2 pH Lactate PCO
2
/ PO
2 pH Lactate
Three processes:
• Bohr / Root shift
• Salting out
• Counter-current diffusion
Bladder caps
Pre-rete Vein
Secretory bladder ref. D 42

Root effect
O
2
Saturation is not reached even if sufficient O
2 available!
higher pH
(gills)
Subunit cooperation
Some subunits fail to load O
2 much lower pH
(retina / swimbladder)
Partial pressure of oxygen (PO
2
)
Decreased capacity under acidic conditions
43