Soft internal anatomy, respiration, & osmoregulation

Lecture 4

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

Skeletal (voluntary) muscle

Myosepta White vs. Red Muscle

• White muscle—greater proportion– Low blood supply– Burst swimming—anaerobic• Few mitochondria• Fatigues quickly• Burns glycogen

– Energy storage• Muscle mass varies

seasonally

White muscle

4min

The fishing effect

• Red muscle—high blood supply • Sustained swimming—aerobic respiration

• Many mitochondria• Lipids used as energy source

– May also power pectoral fins

Red muscle

Alimentary canal—how is it different?

• Esophagus—often has tastebuds and very flexible

• Length of intestine varies– Elasmobranchs—spiral valve

• Pyloric caeca—

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 aRete Mirabile

• Example: countercurrent heat exchange– Endothermic fishes

Countercurrent Exchange Systems

Muscles in body core—

heat produced

Gills—heat lost

Rete Mirabile

Heat flows from vein to artery,as long as a gradient exists

20o

15o10o

15o10o

5o

Concurrent Exchange Systems

Muscles in body core—

heat produced

Gills—heat lost

20o

15o

12o12o

10o

5o

12o12o

12o12o

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

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 glandOvalRete

MirabileSwim bladder

Swim bladder

Swim bladder—Physoclistous

ReteMirabile

Gas Gland

One of 1000+capillaries enteringgas gland through

rete mirabile

Swim bladder

Swim bladder—Physoclistous

Gas Gland

• 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.

Swim bladder

Swim bladder—Physoclistous

Gas Gland

Solution: Countercurrent Concentration• Rete Mirabile retains gases• Gas concentration ↑ • Equilibrium reached

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

• Barotrauma—

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?

Swim bladder—other uses

Extrinsic

Intrinsic

• Sound waves passing through fish vibrate swim bladder

• Hearing specialists have connection from swim bladder to inner ear– More sensitive hearing

Swim bladder—other uses

Weberian ossicles

4 “chambered” heart

Cardiovascular system

• Fish hearts relatively small and size varies by species• Heart ____________ ____________ Heart• Dorsal aorta is main artery to body

Sinus venosus

Bulbusarteriosus

Ventricle

Atrium

Valves prevent backflow

VentralAorta

• 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

Cardiovascular system

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

PoeciliidaeAquatic surface respiration

VentilationFish pass water over gills to extract O2

– O2 diffuses across membrane down gradient

Ventilation achieved using mouth, buccal chamber, and operculum

Mouth open

Buccal chamberexpanding

Opercularvalve shut

Mouth closed

Buccal chambercontracting

Opercularvalve open

Same system used by many species when feeding

GillsEfficient at extracting O2 from water• Large surface area• Thin epithelial membrane• Countercurrent blood flow

Surface area varies 7-fold

Gills—countercurrent blood flow• O2 only diffuses if

concentration gradient exists– Countercurrent flow O2 in

water always higher than blood

Other types of ventilationRam ventilation—– Some pelagic predators dependent– Must keep swimming– Many species use both methods

Spiracles in elasmobranchs—

Endothermy in Fishes

OsmoregulationOsmoregulation—Fish are osmoregulators—

Thin gill membranes allow gas transfer, but this comes at a cost……….?

Why do freshwater and marine fishes have opposite problems?

Osmoregulation—fresh vs. saltwaterH2O Salts

H2OSalts

Diffusion

Active transport

SaltsDilute urine

Drink

SaltsConcentrated urine

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

Osmoregulation—kidneys & bladder

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

Osmoregulation—gills

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—

Gill membrane

Blood vessel

Salt water

Urea increasesosmotic pressure

Coelacanth