1. Hypo-osmotic - Hypo-ionic Regulation Medium osmolarity (mOsm) 0 1000 ECF osmolarity (mOsm) e.g. Uca, Artemia marine teleosts

2. Crustacea: Uca - hemolymph Na = 447 mM in 175% sw (~ 800 mM) Artemia - hemolymph Na = 300 mM in as much as 4-5 M NaCl !!!

3. 500 mM NaCl 1000 mOsm 200 mM NaCl 400 mOsm H2OH2O ion(s) Problems: osmotic water loss diffusive salt gain H 2 O ions Solutions: drink sea water ion uptake by gut active salt extrusion Marine Teleost

4. ant.post.mM Fluid absorption across teleost gut: NO ACTIVE TRANSPORT OF H 2 O! Must move ions and cause H 2 O to move by osmosis s.w. Na = 450 K = 9 Cl = 520 Blood: Na = 200 K = 4 Cl = 190 Na = 100 K = 6 Cl = 90 Na = 20 K = 0.8 Cl = 50 ions H2OH2O >95% of salts absorbed ~75% of H 2 O absorbed

5. lumen of gut blood (serosa) Cl - HCO 3 - ATP ADP + P i Cl - H+H+ Na + ATP ADP + P i Na + K+K+ Cl -

6. CC - mitochondria-rich chloride cell AC - accessory cell, PC - pavement cell From Evans et al. (1999) J. Exp. Zool. 283: 641-652.

7. Apical pit of chloride cell on surface of gill lamella From Evans et al. (1999) J. Exp. Zool. 283: 641-652.

8. Gill epithelial cell Blood

9. Isosmotic - Hypo-ionic Regulation mM NaClTMAO + ureamOsm Sea Water45050001000 Hagfish Plasma54955001150 Teleost Plasma1602000 400 Elasmo. Plasma290300 350-4001000

10. S.W. 500 mM NaCl 1000 mOsm 300 mM NaCl 1000 mOsm ion(s) Problem: Diffusive salt gain Solution: Active salt excretion

11. Elasmobranchs retain nitrogenous compounds as osmotic effectors: H 2 N C = O H 2 N urea CH 3 H 3 C N = O CH 3 trimethylamine oxide (TMAO)

12. mM NaClTMAO + ureamOsm Sea Water450500 01000 Plasma2502504201000 Urine250250110 800 Rectal gland fluid500500 201000 Urea and TMAO are reabsorbed from the urine. Salt is excreted via rectal gland and chloride cells in the gills.

13. Hyperosmotic-Hyperionic Regulation Medium osmolarity (mOsm) 0 1000 ECF osmolarity (mOsm) e.g. freshwater fish & crustaceans e.g. estuarine crustaceans

14. 150 mM NaCl 300 mOsm 2 mM NaCl 5 mOsm H2OH2O ion(s) Problems: osmotic water gain diffusive salt loss Freshwater crayfish, Astacus H 2 O ions antennal gland Solutions: produce copious urine urinary salt loss decrease permeability active ion uptake

15. NaCl Na + Cl - Freshwater Fish (Teleost) Voluminous, dilute urine Don’t drink the water

16. WaterGill Epithelium