Lecture 17. Osmoregulation
Question for Students: Active fish have higher relative surface areas than inactive fish.
Why don’t all fish have high relative surface areas? What is the cost?
Answer – Other things can diffuse across these membranes too.
A. H20, NaCl [Na+] [Cl-], Ca2+, K+, Mg2+, SO42+
a. activities of enzymes, shape of DNA, active of DNA polymerases are
affected by ion concentrations in fish. Out side of limits, they damage proteins & lead to
cell death.
2. Particular task of animal depends on the environment in which they are found.
slide with ion concentrations for different types of water
A. Rainwater – low in dissolved ions, low pH
- CO2 diffused into H2O, forms carbonic acid & lowers pH to 5.6
1. Acid rain in NE – pH as low as 4
a. sulfur dioxides & nitrous oxides further lower pH
b. a problem in some places for fish
- NE US water on granite – gives up little ions, low pH
- water on clay  ions are diffused into water and pH ↑
2. River water usually has a higher level of ions than rainwater
3. Hard water – that typically buffered by limestone is even higher.
B. Brackish water – occurs where rivers meet sea and salinity is intermediate
between fresh & sea
C. Sea water – high levels of all ions.
D. Hypersaline – Dead Sea, Great Salt Lake – salt is too high – no vertebrates
can live there.
What must the fish do?
- maintain proper H2O
- maintain proper salt/ion levels
salts/ion diffuse (high conc.  low conce.)
water moves from low osmolarity to high osmolarity
Molarity
(specific component) -
Osmolarity
(total solute)
1M glucose
1M NaCl
-
1 Osm
2 Osm (Na+ / Cl-)
1M CaCl2
-
3 Osm (Ca+ / Cl- / Cl-)
Strategies
1. Osmoconformers – osmolarity matches that of environment
2. Osmoregulator – osmolarity differs from environment – must constantly
regulate water levels.
3. Ion conformers – ion concentrations matches that of environment.
4. Ion regulators – ion conc. differ from environment – must constantly regulate
ion levels
Go through examples
hagfish
similar ion conc. & osmolarity to seawater
--osmoconformer & ion conformer
-- note that it occurs under a very narrow salinity range
shark
- similar Osm to sea water  no need to regulate H2O
- different ion conc.  need to regulate ions  keep out salts
-rectal gland that pumps salt into feces
osmoconformer, but an ionregulator
toadfish
-needs to regulate both H2O & ions
goldfish
-needs to regulate both H2O &ions
fw stingray
- needs to regulate both H2O & ions
How to f.w. and s.w. teleosts differ in their osmoregulatory demands?
Bony Fish (Osteichthyes)
FW
Problem: ions diffuse out
H2O goes in
Solutions:
do not drink
pump in salts at gills
make huge amounts of dilute urine (to get
H2O out)
absorb salts from food in gut
SW
Problem: Ions diffuse in
H2O goes out
Solutions:
drink like a fish!
pump out salts at gills
make small amounts of conc. urine (to keep
H2O in)
secrete out salts through kidneys
Excretion
Waste & Metabollic Processes – What to Excrete
sugar - CO2 & H2O
fats – CO2 & H2O
AA – CO2, S, N
nucleic acids – CO2, P, N
H2O (see above), CO2  gills somewhat (read also in book how to deal with this),
S & P  gut
N is the problem  forms NH3 which is very toxic  messes up pH & Fe transport
toxic at low levels toxic > 10^-5 M
NH3 can’t be recycled
Also, misc. toxins in food.
NH3 - ammonia
urea
Nitrogenous Waste
most toxic
aquatic animals use this – fish vent most
NH3 at gills; other animals put in urine
need H2O to dilute
cheap
more expensive
NH3 ------urea
(4Atp)
less toxic than NH3
requires less H2O
Why ever use urea?
- sharks for osmoregulatioin
- lungfish – use NH3 in water, switch to urea while estivating