Soft internal anatomy, respiration, & osmoregulation

1. Soft internal anatomy, respiration, & osmoregulation Lecture 4

2. Skeletal (voluntary) muscle • Relatively high proportion of fish is muscle • Muscle segmented into myomeres • Fibrous septa attach to skin and backbone

3. Skeletal (voluntary) muscle Myosepta White vs. Red Muscle

4. White muscle • White muscle—greater proportion • Low blood supply • Burst swimming—anaerobic • Few mitochondria • Fatigues quickly • Burns glycogen • Energy storage • Muscle mass varies seasonally The fishing effect 4 min

5. Red muscle • Red muscle—high blood supply • Sustained swimming—aerobic respiration • Many mitochondria • Lipids used as energy source • May also power pectoral fins

6. Alimentary canal—how is it different? • Esophagus—often has tastebuds and very flexible • Length of intestine varies • Elasmobranchs—spiral valve • Pyloric caeca—

7. Countercurrent Exchange Systems • Rete Mirabile—arterial and venous capillaries are closely associated • Flowing in opposite direction • Designed to retain heat, ions, or gases in certain tissues or areas of the body 2 units of a Rete Mirabile

8. Countercurrent Exchange Systems • Example: countercurrent heat exchange • Endothermic fishes Rete Mirabile 5o 10o 15o Muscles in body core—heat produced 10o 15o 20o Heat flows from vein to artery, as long as a gradient exists Gills—heat lost

9. Concurrent Exchange Systems 5o 20o 15o 10o Muscles in body core—heat produced 12o 12o 12o 12o Gills—heat lost 12o 12o

10. Swim bladder—Buoyancy control • Originally evolved as a lung • Two types of swim bladder arrangement • Physostomus fishes have pneumatic duct • More primitive • Gulp and burp air to regulate • Physoclistousregulates filling by adding or removing gases from blood

11. Swim bladder—Physoclistous • Gases diffuse in/out of bladder—down concentration gradient • Partial pressure gradient—the pressure of a gas on a mixture • Oval— • Stretch receptors help regulate • Gas Gland— Gas gland Oval Rete Mirabile Swim bladder

12. Swim bladder—Physoclistous One of 1000+ capillaries entering gas gland through rete mirabile Rete Mirabile Gas Gland Swim bladder

13. Swim bladder—Physoclistous • Cells in gas gland deposit lactate and H+ into capillaries • Reduced pH → hemoglobin dumps O2 • Lactate (solute) reduces gas solubility • H+ + HCO3- → CO2 + H2O • ↑ Partial pressure of O2, CO2, and N2 • Some gas molecules diffuse across Problem: concentration and pressure of gases still not high enough. Most gas does not pass into swim bladder. Gas Gland Swim bladder

14. Swim bladder—Physoclistous Solution: Countercurrent Concentration • Rete Mirabile retains gases • Gas concentration ↑ • Equilibrium reached Gas Gland Swim bladder

15. Swim bladder—depth changes • Volume of a gas changes with pressure • 33 feet rise = double the volume • 66feet rise = • Barotrauma—

16. Swim bladder—other uses Sound production using a sonic muscle • Muscles rapidly contract (vibrate) • Extrinsic sonic muscle—still attached to body • Sciaendae • Intrinsic sonic muscle—only attached to bladder • Triglidae, Batrachoididae http://core.ecu.edu/BIOL/luczkovichj/fishsounds/fish_sounds.htm http://www.fishecology.org/soniferous/fishsongsringtones.htm Purpose of sound production? Extrinsic

17. Intrinsic

18. Swim bladder—other uses • Sound waves passing through fish vibrate swim bladder • Hearing specialists have connection from swim bladder to inner ear • More sensitive hearing Weberianossicles

19. Cardiovascular system Sinus venosus Atrium • Fish hearts relatively small and size varies by species • Heart  ____________  ____________  Heart • Dorsal aorta is main artery to body 4 “chambered” heart Ventral Aorta Valves prevent backflow Bulbus arteriosus Ventricle

20. Cardiovascular system • Fish have a relatively small blood volume • Elasmobranchs somewhat larger • Red blood cell size varies by species • Up to 5x larger than humans • Contain nucleus

21. Challenges of respiration in water • Much lower O2 concentration in water • As temperature increases O2 decreases • O2 can be spatially variable • Salt water holds less O2 than freshwater • Gills require more energy than lungs Poeciliidae Aquatic surface respiration

22. Ventilation Fish pass water over gills to extract O2 • O2 diffuses across membrane down gradient Ventilation achieved using mouth, buccal chamber, and operculum Same system used by many species when feeding Mouth closed Mouth open Buccal chamber contracting Buccal chamber expanding Opercular valve open Opercular valve shut

23. Gills Efficient at extracting O2 from water • Large surface area • Thin epithelial membrane • Countercurrent blood flow Surface area varies 7-fold

24. Gills—countercurrent blood flow • O2 only diffuses if concentration gradient exists • Countercurrent flow O2 in water always higher than blood

25. Other types of ventilation Ram ventilation— • Some pelagic predators dependent • Must keep swimming • Many species use both methods Spiracles in elasmobranchs—

26. Endothermy in Fishes

27. Osmoregulation Osmoregulation— Fish are osmoregulators— Thin gill membranes allow gas transfer, but this comes at a cost……….? Why do freshwater and marine fishes have opposite problems?

28. Osmoregulation—fresh vs. saltwater H2O Salts Salts Dilute urine H2O Salts Diffusion Drink Active transport Concentrated urine Salts

29. Osmoregulation—kidneys & bladder Freshwater fish have larger kidneys • Retain solutes  blood • Salts may also be reabsorbed through bladder Saltwater fish have smaller kidneys • Retain water  blood • Water may also be reabsorbed through bladder Kidneys also remove nitrogenous waste from blood • Ammonia • Most is removed at the gills

30. Osmoregulation—gills Mitochondrial rich cells in gills transport ions (chloride cells) Freshwater fish • Chloride cells take up ions from water • Na+, Cl-, Ca2+ Saltwater fish • Na+, Cl- removed; Ca2+ brought in Diadromous fishes adjust cell function during migration

31. Subclass Elasmobranchii—Osmoregulation • Most of fish diet is protein  ammonia NH3 (toxic) • Elasmobranchs convert NH3 urea • Retained in blood (solute) • Water gained at gills • Rectal gland— Coelacanth Salt water Gill membrane Blood vessel Urea increases osmotic pressure