Endocrine control of osmoregulation in fish

2. Osmosis is the net of movement of solvent molecules
from a region of high solvent potential to a region of lower
solvent potential through a partially permeable membrane.

3. Osmoregulation means the physiological process that an fish uses to
maintain water balance.
The capacity to regulate plasma ions in the face of changing external
salinity is an obvious necessity for fish that live in estuaries or that
move between fresh water and seawater as part of their normal life
cycle.

4.  The need to respond to salinity change may be rapid or slow that
requires the activation mechanisms, differentiation of transport and
synthesis of new transport proteins.
 The critical part of these osmoregulatory
between environmental change and physiological response by the
neuroendocrine system and exist in it integument, gills and intestine.

5. Type of osmotic.
Hypo-osmotic – more H20
Hyperosmotic – less H20
Isosmotic – same concentration
Osmosis

6. Isotonic SolutionHypertonic SolutionHypotonic Solution
A term for solutions of
equal solute
concentration
The solution having a
higher concentration
of solutes.
The solution having a
lower concentration of
solutes.
There will be a net movement of molecules down the concentration
is reachedequilibriumgradient until a point of
Type of solutions

7. Osmoregulation is energetically
costly, depending on
how different the animal’s
internal osmolarity is from the
environment
 how permeable the animal’s
surfaces are to water and ion
movement
how costly it is to pump ions
across membranes.
Osmoregulators can live in a wide
variety of habitats:
 marine
 estuaries
 freshwater
 land.

8. - Maintain isosmotic conditionsOsmo-conformers
(hagfishes)
-High urea content and TMAO (trimethylamine
oxide)
-low permeability to Na+, Cl-
-excrete excess Na+, Cl-
Salt supplementers
(marine
elasmobranchs and
coelacanths)
-Tend to lose water
-replace by drinking gill cells
-pump in water, not salts
Hyposmotics
(marine teleosts)
-Excrete large volumes of water
-gill chloride cells pump in salts
-often euryhaline (tilapia, drum)
Hyperosmotics
(freshwater fishes)

10. Living in freshwater:
Freshwater is 100% H2O.
Fish cells are 98.6% H2O.
Freshwater fish are hyperosmotic (less water).
Problem:
1. lose salt .
2. gains too much H2O by osmosis.
Solution:
1. does not drink .
2. salt absorbed by gills.
3. large volume of dilute urine by kidney.

12. Living in the Ocean:
Seawater is 96.5% H2O .
Fish cells are 98.6% H2O.
Marine fish cells are hypo-osmotic (more H2O) .
Problem:
1. Loses H2O by osmosis.
2. gains too much salt.
Solution:
1. drink lots of water.
2. secrete salt through gills.
3. excrete small amount of concentrated salty urine.

14. Alternative #1 = Osmoconformers
- organism that allows internal salt concentration to
change with the salinity of the water (conform to the
environment).
- Cells are isosmotic.
- Total salts in body balance salts in sea water (marine
algae and most invertebrates).

15. Alternative #2 = Osmoregulator
- an organism that controls internal salt
concentration different from the environment.
- In fish, mammals, birds and reptiles blood is
hypoosmotic so they tend to lose water.
- (sharks save urea). May expend 5-30% of energy
maintaining osmotic balance.

16. There is no single osmoregulatory organ in fishes but several different
organs and systems have a role to play. Most important are:
The rectal glandThe endocrine
system
The kidneysThe gills

17. The fish pituitary hormones are control osmoregulation by maintaining
water and salt balance.
Thyroid gland of salmons and sticklebacks is known to influence
osmoregulation.
Adrenal cortical tissue or inter-renal tissue secretes two hormones.
These are:
 (i) mineral corticoids concerned with fish osmoregulation.
 (ii) glucocor­ticoids, which regulate the carbo­hydrate metabolism,
particularly blood sugar level.

18. The ultimo-branchial gland secretes the hormone calcitonin which
regulates calcium metabolism and to be related with the osmoregulation
Eel calcitonin causes decrease serum osmolarity, sodium and chloride in
Japanese eels.
The caudal neurosecretory system is said to be related with
osmoregulation.
Growth hormone has the capacity to increase the number and size of
gill chloride cells ion transporters involved in salt secretion.

19. Kidneys The shark has two kidneys on either side of the midline.
The shark osmoregulates in a unique way compared to most other
vertebrates. The shark kidney extracts urea from urine and returns
the urea to the blood, whereby it concentrates urea in the blood. In
this way the osmotic pressure of the sharks body fluids are
maintained as high as that of sea water. With this system the shark
does not lose water or gain salts through osmosis.
Rectal glands This is a tube-like extensions of the rectum. This
gland helps the kidney control the salt (NaCl) concentration within
the body. Excess salt is released into the rectum for expulsion.