Osmoregulation in fish Flashcards
Are marine fish hyperosmotic or hyposmotic relative to seawater?
Hyposmotic
Will marine fish gain or lose salts relative to seawater?
Gain
Will marine fish gain or lose water relative to seawater?
Lose
Do marine fish drink water?
Yes
How do marine fish cope with the the hyperosmolarity of the seawater?
They drink seawater and excrete the salt to replenish their internal water
What is the primary organ of salt excretion in marine fish?
Gills
Which ions are excreted from the gills in marine fish?
Monovalent ions. Na+, K+, Cl-
Which ions are excreted from the urine of marine fish?
Divalent atoms. Mg2+ and SO4 2-
Do marine fish still lose water from getting rid of salts?
Yes. Water loss across the gills is passive since the water just follows the monovalent ions by osmosis. The fish will also lose a little bit more making urine to get rid of the divalent atoms
What specialized type of cell gets rid of salts in the gills of marine fish?
Chloride cells/mitochondrial rich cells
What is the primary osmoregulatory organ in all fish?
The gills
Where are chloride cells found?
Gill epithelium
What are 2 characteristics of the chloride cells?
Have tons of mitochondria and have an extensive intracellular tubular system for movement of molecules around the cell
What do the chloride cells excrete? Is the transport active or passive?
Excrete chloride through active transport
Who moved euryhaline pupfish to a saltier environment to determine how their gill structure changed in response to higher salinity?
Karl Karnaky
What happened to the chloride cells in fish exposed to higher salinities in Karnaky’s experiment?
Number and size of chloride cells increased. They had a larger surface area of the basolateral membrane and more extensive intracellular tubular system
What happened to the structure of the gill filaments in fish exposed to higher salinities in Karnaky’s experiment?
Got thicker
Why did Karnaky use radiolabelled ouabain to determine the number of Na+/K+ ATPases in the chloride cells of fish exposed to high salinities?
Ouabain binds to the ATPases and can be detected by microscopy to see how many ATPases there were
What happened to the number and location of Na+/K+ ATPases in fish exposed to higher salinities in Karnaky’s experiment?
Number increased, but location stayed the same
What were Karnaky’s 3 conclusions after the fish gill salinity experiment?
- High solute concentration causes a euryhaline fish to change its gill structure
- Fish increase the size, number, and complexity of the chloride cells
- Increased Na+/K+ ATPase activity and number on the basolateral membrane of the chloride cells
Which transporters are located on the basolateral membrane of chloride cells?
Na+/K+ ATPase, NKCC cotransporter, potassium channels
Which transporters are located on the apical membrane of the chloride cells?
Chloride channels
How do the chloride cells transport chloride ions out of the cell?
The Na+/K+ ATPase establishes a sodium gradient by transporting sodium ions out the cell into the intercellular space. Sodium enters the cell again through the NKCC cotransporter, and the gradient powers the transport of a K+ and 2 Cl- across through secondary active transport. Cl- will leave the cell through the chloride channels on the apical membrane into the water and the K+ diffuses back across the basolateral membrane through the K+ channel through facilitated diffusion. Na+ will then follow the Cl- through the tight junctions between cells or through sodium channels
Are freshwater fish hyperosmotic or hyposmotic relative to the freshwater?
Hyperosmotic
Will freshwater fish gain or lose water relative to freshwater?
Gain
Will freshwater fish gain or lose ions relative to freshwater?
Lose
How do freshwater fish cope with the hyposmolarity of freshwater?
Active take up salts across their gills
Do freshwater fish drink water?
No
Is freshwater fish urine hyposmotic or hyperosmotic relative to the blood? How much do they produce?
Freshwater fish produce high volumes of hyposmotic urine
Why do freshwater fish produce high volumes of hyposmotic urine?
Keeps the ion balance. They excrete all the extra water and retain the ions to keep their osmolarity in check
What are the specialized ion pumping cells found in freshwater fish gills?
PNA cells (Peanut lectin agglutinin antibody)
What are the 2 types of PNA cells?
PNA- cells: acid secreting cells
PNA+ cells: base secreting cells
What ions do the PNA- cells take up and secrete?
Take up Na+ and secrete H+
What ions do the PNA+ cells take up and secrete?
Take up Cl- and Ca2+and secrete HCO3-
What enzyme do the PNA cells in freshwater fish have to maintain pH balance?
Carbonic anhydrase
How do animals that migrate between saltwater and freshwater switch their salt transport depending on which environment they’re in?
Hormones cause the ion transport cells in the gills to change function
Which hormone mediates NaCl transport out of the gills in seawater in animals that migrate between freshwater and seawater?
Cortisol
Which hormone mediates NaCl transport into the gills in freshwater in animals that migrate between freshwater and seawater?
Prolactin
What is a diadromous animal?
Animal that moves between marine and freshwater environments
What is a catadromous animal?
An animal that migrates from freshwater to seawater to breed (eels)
What is an anadromous animal?
An animal that migrates from seawater to freshwater to breed (salmon)
How does the osmolarity of elasmobranch blood compare to the osmolarity of seawater?
Slightly hyperosmotic and hypoionic
How do sharks maintain hyperosmotic and hypoionic blood?
Replace NaCl with organic osmolytes
What are the osmolytes that sharks use to maintain their hyperosmotic and hypoionic blood?
Urea and trimethylamine oxide. Nitrogenous waste products that are reabsorbed from the kidneys by active transport
How does having a high amount of urea in shark blood not denature everything?
Gets counteracted by TMAO
Is there a net influx or efflux of water for sharks?
Influx
How much osmotic pressure do urea and TMAO contribute to the hyperosmolarity of shark blood?
40%
How do sharks gain ions?
Passive diffusion across the gills
How do sharks deal with extra salts?
Rectal gland cells produce secretions that are rich in NaCl. Also get rid of salts and water through their feces
Is shark urine hyposmotic or hyperosmotic relative to the blood plasma? How much do they produce?
Moderate amounts of hyposmotic urine rich in divalent atoms (Mg2+ and SO4 2-)
Which hormone signals the rectal glands in sharks to start secreting salts?
Vasoactive intestinal peptide
What are the transporters in the rectal gland cells? Where are they located?
The receptor for VIP is located on the basolateral membrane, and is a GPCR. The pathway activates NKCC on the basolateral, which bring chloride into the cells. The chloride then leaves through chloride channels on the apical membrane
What is smoltification?
Hormone mediated remodelling of the gills in salmon as part of their development
Which hormone mediates smoltification?
Cortisol
Why is smoltification different from the hormone mediated gill remodelling seen in migratory eels?
Smoltification is related to development and not the salt change, since it happens even before the fish reach the saltwater
