1. Homeostasis: Osmoregulation in elasmobranchs
The difference between marine, eurahyline and fresh water species

2. Osmoregulation The environment the organism lives in Isotonic?
Relationship between solute to solvent concentrations of internal body fluids
The environment the organism lives in
Isotonic?
Hypertonic?
Hypotonic?
Osmolarity = solute/solvent concentration

3. semipermeable membrane between two compartments
water molecules
protein molecules
semipermeable membrane
between two compartments
Fig. 5-20, p.86

4. 1 liter of distilled water
2% sucrose solution
1 liter of
10% sucrose solution
1 liter of
2% sucrose solution
1 liter of distilled water
Hypotonic
Conditions
Hypertonic
Conditions
Isotonic
Conditions
Fig. 5-21, p.87

5. hypotonic solution hypertonic solution
first compartment
second compartment
hypotonic
solution
hypertonic
solution
membrane permeable
to water but not to solutions
fluid volume
rises in second
compartment
Fig. 5-22, p.87

6. water but not to solutes
Hypotonic
Solution
membrane permeable to
water but not to solutes
Hypertonic
Stepped Art
Fig. 5-22, p.87

7. The Challenge Avoid desiccation in an aqueous environment
MARINE ANIMALS
Dehydration
Elimination of excess salt
FRESHWATER ANIMALS
Conserve salts
Eliminate excess water
Elasmo blood and other bodily fluids separated from the surrounding environment by permeable surfaces.
Marine animals face problems of dehydration and the elimination of excess salts
Freshwater animals must conserve their salts and eliminate excess water.

8. Environmental challenges of elasmobranchs
All ureotelic and ureosmotic except potamytrygonid rays
Marine elasmobranchs surrounded by salt; lose water;
need to get rid of excess organic and inorganic compounds
Euryhaline species environment fluctuates
Must handle salt and fresh conditions
Freshwater species
lose salt and electrolytes; need to get rid of excess water

9. Dealing with Environment
Marine : Maintain serum osmolarity = or greater than seawater primarily w/ urea
Little osmotic loss of water
Dilute Seawater or Freshwater: Serum osmolarity reduced
Little diffusion of water inward

10. Players in osmoregulation
Organs
Kidney, liver, gills, rectal gland
Organic compounds
Urea
TMAO trimethylamine oxide
Inorganic ions
Sodium
Chloride
Other salts

11. Umanitoba - Gary Anderson

12. Body Fluid Marine Elasmobranchs
Reabsorb & retain urea and other body fluid solutes in tissues
Serum osmolarity remains just greater than external seawater (hyperosmotic)
Don’t have to drink water like teleosts
Water gained excreted by kidneys
Marine elasmos evolved technique of reabsorbing and retaining urea & other body fluid solutes in tissues so serum osmolarity (solute/solvent concentration) remains just greater than external seawater. \
This reduces need to continuously drink seawater like teleosts do.
Tri-MethylAmine Oxide (TMAO): Acts to counteract the perturbing effects of urea

13. Marine elasmobranchs Plasma solutes and osmoregulation
Different than marine teleosts
Have high osmolarity
Reabsorb and retain high levels of urea and TMAO in their body fluids
Osmolarity remains hyperosmotic to surrounding seawater
TMAO to stabilize proteins and activate enzymes
Water gained across gills is excreted by kidneys
Any salt gained across gills is excreted by rectal gland and kidney

14. Body fluid of euryhaline elasmobranchs
Ammonotelic in frehwater
As salinity increases
Increase urea production and retention
Decrease urea excretion
Increase Na+ and Cl-
Decrease ammonia excretion
Can not produce and retain as much urea as marine spp. (lower osmolarity)
Ex. D. sabina and H. signifier

15. Body fluid of euryhaline elasmobranchs
As salinity decreases
Lower osmolarity (less urea and TMAO) than marine species
Decrease amount of urea produced and reabsorbed
Increased urinary excretion
Loss of sodium and chloride balanced by electrolyte uptake at the gills and reabsorbed by kidneys

16. Bull Shark - Carcharhinus leucas
Eeigen Werk

17. Body Fluid Fresh Water Elasmobranchs
Lost ability to synthesize and retain urea or TMAO
Body fluid solute concentrations relatively low
Freshwater rays abandoned renal reabsorption
Urine is dilute
Ammonotelic
Ex. Potamotrygon rays

18. Potamotrygonidae
Raimond Spekking

19. Urea- production, retention and reabsorption
Occurs in the liver
Retention
In gills
Reabsorption
In kidneys

20. Urea production in liver
Ornithine-urea cycle (OUC)
Glutamine synthetase is crucial enzyme needed for urea production
Euryhaline spp. decrease production of urea when entering fresh water
Freshwater rays lack the enzyme for the biosynthesis to occur
Unsure if urea is produced in other locations
Bacteria hypothesized for being responsible

21. Marine gills retain urea
Do not lose much urea across gills
Gill’s basolateral membrane has high cholesterol to phospholipid ratio levels
Membrane limit diffusion
Active transport of urea by Na+/ urea antiporter energized by Na+/K+ ATPases
Used more for salt regulation and acid/base balance

22. Kidneys reabsorb urea Reabsorption contributes to high urea levels
Minor site of urea loss
Thought to involve active transport
Use urea-sodium pump
Proven in R. erinacea
Second hypothesis for passive transport that has not been proven
Euryhaline spp. decrease renal reabsorption of urea as enter areas of decreased salinity
Increases rate of urine flow to rid system of excess urea

23. Salt regulation Rectal gland secretions
Marine spp. surrounded by high salinity
Rectal gland secretes sodium and chloride
Na+/ K+ ATPases used

24. Osmoregulation by the Rectal Gland
Rectal Gland = Salt secreting mechanism
Migratory elasmos - regressive rectal gland
Non-functional in freshwater rays
Rectal Gland - epithelial tissue gland - concentrates & secretes excess Na & Cl in sharks. large shark liver produces copious amounts of urea, making the shark hyperosmotic to seawater, & thus a shark acts like a fresh water fish, constantly gaining water. Excess salts are concentrated by the rectal gland and secreted.
Marine; diffusion of salts into the body from seawater… rectal gland secretion
Freshwater movement…rectal gland becomes regressive or non-functional as in fresheater rays Potamotrygon

25. Salt regulation Gills Salt uptake Acid/ base balance
Na+/ K+ ATPases even higher in freshwater
Acid/ base balance
Secrete acid
H+ excreted/exchanged for Na+
Run by Na+/ K+ ATPases
Responsible for ammmonia secretion

26. Salt regulation Kidney salt excretion Dilute environment Saltwater
Urine flow increase
Saltwater
Not solely responsible for salt secretion

27. Endocrine Regulation to Regulate Body Fluid Volume and Solute Concentration
CNP - Released from heart
Increase urine production
Stimulate salt secretion from rectal gland
Inhibit drinking and relax blood vessels
AVT
Increase in plasma osmolality
Reduces urine production
RAS
Antagonistic to CNP, reduces urine flow
Increases drinking
Constricts blood vessels
Three key agents involved in regulation of body fluid volume and solute concdentration
Natriuretic peptide system (NP)
Neurohypophysial peptide arginine vasotocin (AVT), Renin Angiotensin system (RAS)

28. Feeding and osmoregulation
Urea is metabolically expensive
5 umol ATP for 1 mole urea
Protein in food is main source of N in urea
Elasmobranches must get adequate food to produce the urea
Why ureotelic and not ammonotelic???

29. Literture cited
Hammerschlag N Osmoregulation in elasmobranches: a review for fish biologists, behaviorists and ecologists. MARINE AND FRESHWATER BEHAVIOUR AND PHYSIOLOGY 39 (3):
Speers-Roesch B, Ip YK, Ballantyne JS Metabolic organization of freshwater, euryhaline, and marine elasmobraches: implications for the evolution of energy metabolism in sharks and rays. JOURNAL OF EXPERIMENTAL BIOLOGY 209 (13):
Pillans RD, Anderson WG, Good JP, et al Plasma and erythrocyte solute properties of juvenile bull sharks, Carcharhinus leucas, acutely exposed to increasing environmental salinity. JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 331 (2):
Pillans RD, Good JP, Anderson WG, et al Freshwater to seawater acclimation of juvenile bull sharks (Carcharhinus leucas): plasma osmolytes and Na+/K+ ATPase activity in gill, rectal gland, kidney and intestine. JOURNAL OF COMPARATIVE PHYSIOLOGY B-BIOCHEMICAL SYSTEMIC AND ENVIRONMENTAL PHYSIOLOGY 175 (1): 37-44

30. Literature cited
Pillans RD, Franklin CE Plasma osmolyte concentrations and rectal gland mass of bull sharks Carcharhinus leucas, captured along a salinity gradient. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY A- MOLECULAR & INTEGRATIVE PHYSIOLOGY 138 (3): 363-