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Ichthyology > Osmoregulation > Flashcards

Osmoregulation Flashcards

1
Q

brine water

A

external environment (prone to wide fluctuations)

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2
Q

Saline water

A

intracellular environment (allows for no variation; Homeostasis)

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3
Q

Brackish water

A

extracellular environment maintains balance between the two (blood, lymph fluid etc.)

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4
Q

homeostasis

A

maintaining steady state equilibrium in internal environment of an organism

involuntary by action of hormones, enzymes + osmoregulatory processes

fish can “pick up and move” if environmental conditions are unfavourable

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5
Q

Osmoregulation

A

active regulation of osmotic pressure of an organism’s fluids to maintain the homeostasis of organism’s water content

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6
Q

homeostasis requires…

A

…requires conc of internal water + solutes to be maintained within fairly narrow limits, HOWEVER, physiological systems of fishes operate in an internal fluid environment that may not match their external fluid environment

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7
Q

Molarity

A

amount of substance (1 mol) per vol (1 litre) of solution

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8
Q

Molality

A

amount of substance (1 mol) per weight (1 kg) of solution

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9
Q

Osmosis

A

movement of water across semi-permeable membrane as result of varying concentrations of dissociated molecules (salts, proteins, ions)

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10
Q

difference between osmolarity + osmotic pressure

A

greater osmolarity = lower osmotic pressure

water flows from high to low

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11
Q

Osmotic regulation - Isosmotic

A

2 solutions that exert same osmotic pressure

intracellular osmolarity = external osmolarity

no water lost or gained: OSMOCONFORMER

many marine invertebrates

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12
Q

osmotic regulation - hyperosmotic

A

a solution that exerts lower osmotic pressure + so attracts water

intracellular osmolarity > external osmolarity

tissues gain water: OSMOREGULATOR

Freshwater fish

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13
Q

osmotic regulation - hyposmotic

A

a solution that exterts a greater osmotic pressure + so loses water

intracellular osmolarity < external osmolarity

tissues lose water: OSMOREGULATOR

marine teleosts

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14
Q

Osmoregulation strategies - aquatic vertebrates? 1st evolved osmoregulatory organ?

A

aquatic vertebrates - gills = chief organs of excretion/osmoregulation

kidneys 1st evolved as osmoregulatory organs in fishes to remove water (freshwater) or conserve water (marine)

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15
Q

4 osmoregulatory strategies in fishes

A
  1. Isosmotic (nearly isoionic; osmoconformers)
  2. Hyperosmotic w/ regulation of specific ions (osmoregulators)
  3. Hyposmotic (marine fish; osmoregulators) (less salty than water around, lose water)
  4. Hyperosmotic (freshwater fish; osmoregulators) (more salty that water around, gain water, dilution)
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16
Q
  1. Osmoconforming (no strategy)
A

HAGFISH
internal salt conc = seawater ; live in ocean, so no regulation required

only vertebrate that = isotonic to seawater - much like many marine invertebrates

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17
Q
  1. Hyperosmotic w/ regulation of specific ions
A

ELASMOBRANCHS
internal salt conc ~ 1/2 seawater
BUT additional 1/2 made up of urea

so total internal osmotic conc = slightly greater than seawater

gill membrane = low permeability to urea so it is retained in fish - because internal inorganic + organic salt conc mimic that of environment, passive water influx + efflux is minimised

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18
Q
  1. Hyposmotic
A

MARINE TELEOSTS
intracellular osmolarity < external osmolarity
(tissue lose water)

Ionic conc. ~ 1/3 of seawater
Drink copiously to gain water
Chloride cells eliminate Na+ and Cl-
Kidneys eliminate Mg++ and SO4–

19
Q

Drinking rates

A

v. high in marine fishes - 10-20% bw d-1 average, may be up to 40% bw d-1 in some spp)

drinking saline water causes dehydration due to increase salt loading

exclude or excrete solutes

20
Q

Water absorption in alimentary canal

A

absorption in gut = still against osmotic gradient

Mechanism:
- solute-linked water transport
- water can be absorbed if linked to monovalent ions (single charge Na+, K+ and Cl-)
- not all solutes absorbed by alimentary canal
- absorbed water has solute loading 1/2 seawater (1/2 osmolarity)

Result:
- an excess of monovalent ions in fish

21
Q

Ion exchange + osmoregulation in marine teleosts

A
  • external (sea) environment 1000 ~mOsm/kg
  • body fluids 400 mOsm/kg

-> drinking sea water
<- water loss over skin + gills
<- active excretion of monovalent ions via chloride cells
<- divalent ions in faeces
<- divalent ions & scant concentrated urine

22
Q

Saltwater teleosts

A

active transport:
->drinking seawater
<- Na+, Cl- chloride cells
<- Mg2+, SO42- faeces, kidneys

passive diffusion:
-> Na+, Cl-, Mg2+, SO42-
-> Na+, Cl-
<- H2O

23
Q

Chloride cell

A
  • carrier protein (passive) carries chloride + sodium ions to enter
  • (active) pump - pumps out sodium + replaces w/ potassium (Na+ K+ ATPase)
  • potassium high in cell + low outside cell = passive transport out of cell
  • abundance of sodium outside cell -> diffuse into seawater
24
Q
  1. Hyperosmotic
A

FRESHWATER FISH
intracellular osmolarity > external osmolarity
(tissues gain water)

freshwater animals constantly take in water by osmosis from their environment

lose salts by diffusion + maintain water balance by excreting large amounts of dilute urine

salts lost by diffusion are replaced in foods + by active uptake across the gills

25
Q

Osmotic regulation by freshwater teleosts

A

Ionic conc. approx 1/3 of seawater

not drink (much)

B-Chloride Cells (fewer, work in reverse)

Kidneys eliminate excess water (ion loss)

ammonium + bicarbonate ion exchange mechanisms

26
Q

Loss of salts in urine has to be balanced by active uptake

A

gill membrane
freshwater -> interior (ATP - active pumps)
Na+ -> (w/ ammonium)
Cl- -> (w/ bicarbonate)

interior -> freshwater (ATP - active pumps)
NH4+ or H+ (ammonium) -> (w/ Na+)
HCO3- (bicarbonate) -> (W/ Cl-)

27
Q

Freshwater teleosts

A

active:
-> don’t drink much
-> Na+, Cl- (ion exchange pumps; B-chloride cells)
<- water (kidneys)

passive:
-> H2O
-> Na+, Cl-

28
Q

Ion exchange + osmoregulation in freshwater fish

A
  • external (freshwater) environment <5 mOsm/kg
  • body fluids 300 mOsm/kg

-> drink v little freshwater
<- water gain over skin + gills, salt loss by diffusion
<- active uptake of monovalent ions via chloride cells
<- some loss of ions in faeces
<- copious dilute urine, so some loss of ions

29
Q

why no fish in low depths

A

hydrostatic pressure can make proteins lose structure

use TMAO to reduce effect

would need so much TMAO + be salty than environment around them

no fish deeper than 8000 metres

30
Q

limiting water uptake

A

diffusion through skin can be limited:
- scales
- thick, relatively impermeable skin, mucous

gills always have thin blood-barrier, h/e (compared to other tissues) major area of water uptake

31
Q

Water uptake

A

drinking rates low; but passive diffusion of water from environment

large Bowman’s capsule (part of kidney) + many glomeruli for filtering water out of blood

32
Q

Freshwater fish produces…

A

…copious dilute, hypotonic urine (16-55 mOsm/kg)

glucose reabsorbed in proximal tubule of kidney, 99% salts reabsorbed in distal tubule and bladder

33
Q

Ionic + osmoregulation in marine elasmobranchs

A

marine elasmobranchs = slightly hyperosmotic
(tissues gain water)

external environment 1000 mOsm/kg
body fluids 1100 mOsm/kg

-> salts in food
-> ions into gills & urea out
<- divalent ions + little a urine
<- monovalent ions excreted by rectal gland

34
Q

How do sharks maintain high solutes in tissues?

A

slightly hyperosmotic body fluids by retention of nitrogenous solutes, esp Urea, Betaine, Sacrosine + some amino acids (Taurine & B-alanine)

> 95% of urea retained

skin + gills of elasmobranchs impervious (not allowing entrance or passage) to urea

35
Q

Monovalent ions enter the body and are excreted by the…

A

…rectal gland (v similar function to chloride cells)

36
Q

The impact of urea

A

Urea conc 0.4 M in blood of elasmobranchs

100x conc that most vertebrates would die from

most proteins denature at a urea conc of 0.5 M

some proteins + enzymes need high urea conc to function effectively, others are resistant to effects of urea

Trimethylamine oxide TMAO + other methylamine substances protect proteins from urea

THE ENTIRE METABOLISM OF SHARKS IS ADAPTED TO THE PRESENCE OF UREA!

37
Q

Euryhaline fish

A

tolerate wide range of salinities
e.g. intertidal fish, estuarine fish

38
Q

Stenohaline fish

A

little tolerance to varying salinity
e.g. most fish, both freshwater and marine

39
Q

Euryhaline conditions

A

s-t fluctuations in osmotic state of environment, e.g. intertidal zone or estuaries where salinity can range from 10 to 34 w/ daily tidal cycle:

fish have both kinds of chloride cells
- when salinity = low, operate more like FW fishes
- when salinity - high, operate more like marine fishes
- kidneys function only under low salinity conditions

40
Q

Diadromy

A

Diadromous fishes (spend part of life in SW, part in FW)
- catadromous (migrate seaward)
- anadromous (migrate up river)

hormone-mediated changes associated w. metamorphosis; convert form FW adaptations to SW or vice versa, depending on direction of migration

fish inhabit 2 v different environments, each w. little variation in salinity, but have l-t adaptations for the change from one to the other

migrate either up rivers (salmon) or to the sea (eel) to spawn

41
Q

Freeze resistance

A

marine teleosts (hypotonic) - fishes might fave freezing

less salty than water - problem for cold water - freezing

42
Q

Solution for Antarctic fish

A

Macromolecular antifreeze compounds
- peptides (protein) (rich in alanine)
- glycopeptides (carbohydrate/protein) (rich in alanine)

molecules absorb (attach) to ice crystal surface + interfere w/ ice crystal growth (disrupt matrix)

why is this important?
ice ruptures cells; hinders osmoregulation

43
Q

Stress

A

stressors (handling, sustained exercise, e.g. escape from predator pursuit) cause release of adrenaline (epinephrine)

adrenaline causes diffusivity of gill epithelium to increase (become “leaky” of water + ions)

This accentuates the normal osmoregulatory challenge for freshwater or marine fishes

44
Q

How to reduce stress in fish

A

such as in hatchery/aquaculture conditions, when transporting fish, handling etc.

minimise the osmotic challenge by placing fish in conditions that are closer to isosmotic
- add salt to freshwater
- dilute salt water with freshwater

Ichthyology (10 decks)

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