Energetics in Fish Gills
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Transcript of Energetics in Fish Gills
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Oxygen, Metabolism
&
Energetics
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Introduction
Most terrestrial vertebrates have internal lungs that mustbe ventilated throughbidirectionalmovement of air to
replenish the oxygen (O2) supply
Most fish have external gills that are ventilated by aunidirectionalflow of water, by pumping or swimming
Fine sieve structure of gills very efficiently extracts O2
from water.
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Efficient O2 uptake is vital to fish because of its low water
solubility.
Introduction (cont.)
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Efficient O2 uptake is vital to fish because of its low water
solubility.
Solubility decreases with increased temperature & salinity!
Introduction (cont.)
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Oxygen solubility determined by
temperature
Temp (C) O2 con. at sat.
(mg/l)Fresh
O2 con. at sat.
(mg/l)Salt
0 10.3 8.0
10 8.0 6.3
20 6.5 5.3
30 5.6 4.6
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Efficient O2 uptake is vital to fish because of its low water
solubility.
Solubility decreases with increased temperature & salinity!
Also, metabolic rate (demand for O2 ) increases as
temperature rises. (How does this affect nutrition?)
Introduction (cont.)
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Efficient O2 uptake is vital to fish because of its low water
solubility.
Solubility decreases with increased temperature & salinity!
Also, metabolic rate (demand for O2 ) increases as
temperature rises. (How does this affect nutrition?)
What does this mean to fish??
Introduction (cont.)
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In warm water...fish need to extract MORE O2 from LESS!
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Gills
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Gills are the main
site of gas exchange
in almost all fishes.
The gills consist of bony or
stiffened arches (cartilage) that
anchor pairs ofgill filaments.
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Numerouslamellae protrude from
both sides of each filament and are
the primary sites of gas exchange.
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Microscopic gill structure:
showing gill filament and
lamellae (Red blood cells
evident.)
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How can fish remove 80 -
90% of O2
available from
water?
Short diffusion distance at gill
site
Large surface area for diffusion
at gill site
Counter current exchange of
gases at gill site
Large volume of water passes
over gills
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1. Fill mouth cavity (open
mouth, expand volume of
mouth, expand volume of gill
chamber with operculum
closed)
2. Fill gill cavity (close mouth,
squeeze mouth cavity, expand
gill cavity, with operculum
closed)
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3. Expel water from gill
cavity (squeeze mouth and
gill cavities, open operculum)
4. Reset for next cycle
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Oxygen Exchange in
Fish
Fish employ thecountercurrent
system to extract O2
from the water.
This system moveswater flowingacross the gills, inanopposite
direction to theblood flow creatingthe maximumefficiency of gasexchange.
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Blood flow through lamellae
is from posterior to anterior.
Water flow over lamellae isfrom anterior to posterior.
Counter-current allows fordiffusion from high O2 inwater to low O2 in bloodacross entire length oflamella.
* When he blood and waterflows in the same direction,theco-currentsystem, it willinitially diffuses largeamounts of oxygen but theefficiency reduces when thefluids start to reach
equilibrium.
Countercurrant*
Close-up!
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Lets Do the Math...
4 gill arches on each side of body
2 rows of gill filaments on each arch (demibranchs)
100s filaments per demibranch - closely spaced
1000s lamellae per gill filament
gill area = 10 to 60 times that of body surface area, depending
on species!
HUGE potential to extract Oxygen from water!
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Auxiliary Respiratory Structures
Skin - diffusion of oxygen from water into dense network
of capillaries in skin (eels), Thin skin (larval fish) supplies
50% of O2 needed.
Swim bladder - vascularized physostomous swim bladders
(gars)
Lungs - modified swim bladder (lungfishes)
Mouth - vascularized region in roof of mouth (electric eel,
mudsuckers)
Gut - vascularized stomach or intestinal wall (armored
catfish, loaches)
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Branchial vs. Ram Ventilation
Branchial
Mouth
Pharynx
Operculum
Branchiostegals (filaments, lamella)
Ram
Uses same parts, but not the pumping energy required. Sharksprimarily. Once swimming speed is achieved...no need toactively vent buccal cavity. However, this can only be usedconsistently by strong swimmers (sharks, tuna).
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7
6
5
4
3
2
1
05 pm 10 pm 5 am
Measured values
Projected values
Dissolved O2mg/l
Practical Application of This Knowledge!Projected Dissolved Oxygen Levels
Time of Day
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Hemoglobin (Hb) of Fish Erythrocytes
Primary means for transporting oxygen
In some fish up to 15% may be in plasma
A few fish have no Hb (rare situation)
Environmental oxygen high
Low metabolic requirements
Special cardiovascular adaptations
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Fish Hemoglobin Characteristics
Structure is different in different fish
Monomeric
Single-heme peptide molecules
Found in Agnatha
Tetrameric
Four peptide chains
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Fish Hemoglobin Characteristics
May differ in many features
Composition of amino acids
Affinity for oxygen
Some salmonids have up to 18 different Hbs
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Having Different Hemoglobin Types
Different Hbs have different responses to:- temperature
- oxygen absorption
Allows fish to deal with changing conditions
Important for migratory species
Some fish gain or lose types as they age
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Blood Oxygen Affinity
pH
Decreasing pH decreases Hb affinity for O2
Often associated with carbon dioxide
Carbon dioxide
Increase in CO2 drives off O2 (Bohr effect)
Decrease in blood pH magnifies Bohr effect
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Blood Oxygen Affinity
TemperatureIncrease in temperature depresses oxygen
affinity and capacity
Results in fish having narrow temperaturetolerances
Organic phosphate
ATP depresses O2 affinity
Urea increases O2 affinity
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How do you inflate a swim bladder?
Gas gland is location of action in wall of swim bladder
(rete mirabilewonderful net and surrounding tissues)
Need to pry O2
molecules from Hb molecules in gas gland
Need to accumulate enough O2 (>pO2) in solution in blood
plasma to generate a diffusion gradient from distal end of
rete mirabile into lumen of swim bladder
How???
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Prying O2 from Hb
Change of pH in blood causes change in bond strength of Hb for O2
Bohr effect--decrease in affinity of Hb for O2 due to decreasing pH or
increasing pCO2
affinity: strength of attraction of Hb for O2
Rooteffect--decrease in capacity of Hb for O2 due to decreasing pH or
increasing pCO2 (extreme Bohr effect)
capacity: total quantity O2 of that Hb can carry
more active species tend to have greater Bohr & Root effects
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0 80 1600
100
50
pO2 mm Mercury
%Saturatio
nofHb pH 8.02
pH 7.47
Air saturation
affinity
capacity
Bohr
Root
Effect of pH on Hb*--2 components
*data for winter flounder
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How to cause pH to drop in tissues of gas
gland?
Regular metabolic processes result in release of H+, either
from glycolysis (lactic acid) or aerobic metabolism (CO2)
Increase metabolic activity in tissues surrounding rete
mirabile = decrease of pH
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How to cause free O2 to accumulate in
distal end of rete?
Another counter-current exchange system:
long capillaries that fold back on self
afferent (incoming) part of capillary experiences drop
in pH, Hb loses O2
efferent (outgoing part of capillary has higher partial
pressure (concentration) of dissolved O2 than afferent,
so
O2
diffuses into afferent arm, causing supersaturation
of blood at distall end of rete with O2
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Advantage of Bohr Effect
TissuesGills
blood circulation
pH lowerpH higher
pCO2 higherpCO2 lower
lactic acidno lactic acid
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Function of Rete Mirabile
1. Hemoglobin saturated with O2 (O2heme)
plasma O2 low (p O2)
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Counter-current multiplication system
afferent blood
efferent blood
O2hemepO2
O2heme pO
2
pO2
sw
im
bladder
O2heme
pO2
lactic acid
1 2
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Function of Rete Mirabile
2. Lactic Acid Secretions
heme dumps O2to plasmapO2diffuses into swim bladder to equil.
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Counter-current multiplication system
afferent blood
efferent blood
O2hemepO2
O2heme pO
2
pO2
sw
im
bladder
O2heme
pO2
lactic acid
1 2
3
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Function of Rete Mirabile
3. Multiplying effect: pO2 diffuses from efferent capillary to
afferent cap. Also, longer capillaries yield more efficientexchange of oxygen, higher pressures
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What about CO2?
Okay...we got the O2 inside...how do we get the CO2outside?
Again, blood also is involved in CO2 transport.
Three mechanisms to move CO2 outside cell to be excreted.
(1) Simple dissoution in plasma
(2) Binding to proteins/formation of carbamino groups.
(3) Dissociation into carbonic acid by pH change (greatestamount of CO2 transformed this way.)
Chl id Shif
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dissociation is slow
HHbO2 + O2
O2
CO2 + HbO2
HbCO2 + O2
O2
Chloride Shift
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Buoyancy strategies
1. Low density compounds
2. Lift generated by swimming
3. Reduction of heavy tissues
4. Swim bladder (air bladder)
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1. Low density compounds:
Substance Specific Gravity
Bone 2.0
Muscle 1.05
Cartilage 1.1
Freshwater 1.002 @20C
Saltwater 1.072 @20C
Lipids 0.9-0.92
Squalene 0.86
Advantages/disadvantages
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2. Lift generated by swimming:
lift
lift
thrust
sharks Advantages/disadvantages
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3. Reduction of heavy tissues
umbrella mouth gulperEurypharynx pelecanoides
deepwater fishes
Advantages/disadvantages
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4. Swim bladder
low density
adjustable
most osteichthians
lost secondarily in some species
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Two types of swim bladders:
Physostomous
pneumatic duct
soft-rayed teleosts--herrings, salmonids, catfishes,
cyprinids, eels, etc.
Physoclistous
blood/circulatory system
spiney-rayed teleosts--Acanthopterygii, sunfishes, perch,
most marine fishes
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Effects of depth on swim bladder volume
pressure increases 1 ATM/10m
swim bladder must be adjustable
Physostomous fishes adjust volume by gulping or
spitting air. mostly shallow water species
gas-spitting reflex
gulp air at surface
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Physoclistous inflation/deflation
circulatory system--source of gases
rete mirabile (wonderful net) --inflation
oval window--deflation
Problem: fish need greater pressure in swim bladderthan is achieved by equilibrium with blood gases
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Physoclistous swim bladder
Pressures up to 300 ATM in some deep sea fishes
Gases mostly O2, some CO2 and N2
Guanine crystals in SB wall reduce permeability
Deflation occurs at oval window
dense bed of capillaries on SB wall gasses diffuse into blood
mucus layer covers window during inflation
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Summary:
Diffusion of O2; controlled by structure & function
Relationship O2 bound to Hb vs. O2 in plasma
Effect of pH on affinity/capacity of Hb for O2
Counter-current multiplier
length of capillaries
counter-current flow of blood
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Growth &
Metabolism
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Growth:
Longevity
unconfirmed reports of carp 200-400 yr.
authenticated records for carp 50 yr.
large fish-few > 12-20 yr.
some marine spp > 100 yr. thornyspines, orange roughy
many small spp-2 yr. or less (sardines, anchovies)
Note: aging with scales, bones, otoliths
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Many Generalities:
Sexual Dimorphism: females can be larger than males
Growth rate a function of temperature
Longevity inversely proportional to temperature
Stress reduces growth
Dominance hierarchies - dominant get food
Overcrowding can lead to stunting
Indeterminate growth - grow throughout life
Growth highly variable - decreased weight gain
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Bioenergetics continued:
Energy Budget:
I = M + G + Ewhere: I = ingested energy
M = energy expended for metabolism
G = energy stored as growth
E = energy lost to environment
Bi ti E B d t
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Bioenergetic Energy Budget:
Bi ti E B d t
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Bioenergetic Energy Budget:
I
Bioenergetic Energ B dget:
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Bioenergetic Energy Budget:
I M
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Bioenergetic Energy Budget:
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Bioenergetic Energy Budget:
GI M
heat
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Bioenergetics continued:
Ex: M = energy for body repair
maintenance
activity
digestion
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Bioenergetics continued:
Ex: E = energy in feces
ammonia, or urea
mucus
epidermal cells
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Terms:
Standard Metabolic Rate
maintenance met.; no growth, no activity
Routine Metabolic Rate
typical met.; routine growth & activity
Active Metabolic Rate
max. aerobic metabolism
Factors Affecting Growth: Temperature
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Factors Affecting Growth: Temperature
Temperature
MetabolicRate
standard
activeroutine
scopeactivity
growth{Where would
growth be best?
Factors Affecting Growth: Temperature
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Factors Affecting Growth: Temperature
Temperature
MetabolicRate
normal O2reduced O2
reduced scope
reduced growth
Factors Affecting Growth: Dissolved oxygen
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Factors Affecting Growth: Dissolved oxygen
R
outineMetabolism
0 84
O2 regulator (most species)
critical O2 concentration
O2 conformer