Osmoregulatory Systems in Fishes
Maintaining homeostasis with respect to
solute concentrations and water content
• Sistem Osmoregulasi / regulatorosmotik/osmoregulator
ialah sistem pengaturan keseimbangan tekanan osmotik
cairan tubuh (air dan darah) dengan tekanan osmotik
• Pengaturan tekanan osmotik cairan tubuh yang layak
bagi kehidupan ikan, sehingga proses-proses fisiologis
tubuhnya berfungsi normal.
• Homeostasis = maintaining steady state equilibrium
in the internal environment of an organisms
• Solute homeostasis = maintaining equilibrium with
respect to solute (ionic and neutral solutes)
concentrations (i.e. salts)
• Water homeostasis = maintaining equilibrium with
respect to the amount of water retained in the body
fluids and tissues
Osmoregulation in different environments
• Each species has a range of environmental osmotic
conditions in which it can function:
– stenohaline - tolerate a narrow range of salinities
in external environment
– euryhaline - tolerate a wide range of salinities in
external environment
• short term changes: estuarine - 10 - 32 ppt,
intertidal - 25 - 40
• long term changes: diadromous fishes (salmon)
Four osmoregulatory strategies in fishes
• Isotonic atau isoosmotik : jika tubuh hewan mempunyai
tekanan osmotik cairan = tekanan osmotik lingkungan
• Hipoosmotik : jika tekanan osmotik cairan tubuh relatif
konstan lebih rendah daripada lingkungannya (Ikan air
• Hiperosmotik : jika tekanan osmotik cairan tubuh relatif
konstan tinggi daripada lingkungannya (Ikan air tawar)
Osmoregulation in marine and freshwater fish
Marine fish face two problems: they tend to lose
water and gain ions.
Freshwater fish face two problems: they tend to
lose ions and gain water.
concentration = seawater.
However, since they live in the ocean....no regulation required!
Komposisi garam dalam darah hagfish menyerupai air laut
sehingga hagfish tidak melakukan osmoregulasi sehingga
disebut isotonis
For the most part, marine invertebrates are in osmotic equilibrium with the
seawater. That is, their salty internal fluids hold as much salts as does the
surrounding aquatic medium.
Stated another way, the principal ions that are found in the fluids that
bathe the cells of the body are the same, and occur in approximately the
same concentrations, as those found in seawater.
There is no problem of water balance—the rate of diffusion of water into
the body is the same as the rate at which water diffuses out. Under
conditions such as this, we say the animals exist in an isotonic
environment (iso means “the same”).
Elasmobranchs (sharks, skates, rays, chimeras)
Maintain internal salt concentration ~ 1/3 seawater, make up the rest of
internal salts by retaining high concentrations of urea & trimethylamine
oxide (TMAO).
Bottom line…total internal osmotic concentration equal to seawater!
How is urea retained?
Gill membrane has low permeability to urea so it is retained
within the fish. Because internal inorganic and organic salt
concentrations mimic that of their environment, passive
water influx or efflux is minimized.
Marine elasmobranchs have solved the problem of
osmoregulation in an entirely different way. They have evolved
a specialized segment of the nephron that reabsorbs urea and
returns it to the blood.
Osmoregulation in a marine shark. The concentration of solutes in the
body fluids is greater than in the outside medium. Open arrows indicate
movement of substances by passive diffusion, closed arrows indicate
movement of substances by active transport mechanisms
What about rapid ion flux?
• Short-term fluctuations in osmotic state of
environment, e.g. in intertidal zone or in
estuaries where salinity can range from 10 to
34 ppt with the daily tidal cycle:
– these fish have both kinds of chloride cells
• when salinity is low, operate more like FW fishes
• when salinity is high, operate like marine fishes
• kidneys function only under low salinity conditions
Diadromy takes two general forms:
1. Anadromy: Adults spawn in freshwater; juveniles move
to saltwater for several years of feeding and growth, and
then migrate back to freshwater to spawn.
Chinook Salmon (Oncorhynchus tshawytscha
2. Catadromy: Adults spawn at sea; juveniles migrate to
freshwater for several years to feed and then return to the
sea to spawn
American eel (Anguilla rostrata)
What about stress??
• Stressors (handling, sustained exercise such as escape
from predator pursuit) cause release of adrenaline
(epinephrine) - for mediating escape, etc.
• Adrenaline causes diffusivity of gill epithelium to
increase, i.e. “leaky cell membranes” water & ions)
• This accentuates the normal osmoregulatory challenge
for FW or marine fishes
Osmoregulatory organ
Merangkum materi tgl 15 (pengertian difusi,
osmosis, osmoregulasi air laut&air tawar,
osmoregulasi elasmobranch)
*silahkan dicari fungsi dari organ
osmoregulasi di atas dan dikumpulkan
hari jumat jam 11.30-12.30 di ged. D
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