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 4
min
The fishing
effect

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
Heat flows from vein to artery,
as long as a gradient exists
20o
15o
10o 5o
Muscles in
body core—heat produced
Gills—heat lost

9. Concurrent Exchange Systems
Muscles in
body core—heat produced
Gills—heat lost

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
Physoclistous regulates 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—
Oval
Gas gland
Rete
Mirabile
Swim bladder

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

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

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

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

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

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. Same system used by many species when feeding
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 open
Buccal chamber
expanding
Opercular
valve shut
Mouth closed
contracting
valve open

23. Gills Efficient at extracting O2 from water Surface area varies 7-fold
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
Diffusion
Active transport
Salts
Dilute
urine
Drink
Concentrated

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