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Soft Anatomy
Chapter 4
Fish Muscle
Muscle types
• Fish have the same three basic types of muscles as other
vertebrates: skeletal, smooth, and cardiac.
• Skeletal: Voluntary, used for locomotion, comprises the
majority of the fish’s muscle mass.
• Smooth: Involuntary such as intestine, many organs, and
the circulatory system.
• Cardiac: Heart
Skeletal Fish Muscle:
•Essentially three types of fish muscle: red, white, pink.
•Red muscle (oxidative): Highly vascularized, myoglobin
containing tissue used during sustained swimming. Small
diameter and high blood volume = rich O2 supply!
Presence leads to strong flavor in some fishes (tuna).
•White muscle (glycolytic): Little vascularization. Used
during “burst” swimming. Large diameter fibers.
•Pink muscle: This one is sort of in between red and
white. Serves in sustained swimming, but not to the extent
that red muscle is used.
Red vs. White Muscle Fibers
Capilary beds
Muscle fiber density
Myoglobin content
Glycogen content
Muscle mass
Alimentary Canal
• Essentially the gastrointestinal tract (GI).
• Two parts: (Antierior) mouth, buccal cavity, pharynx
(Posterior) esophagus, stomach, intestine, rectum.
• Mouth to esophagus & rectum is comprised of voluntary
muscle while the stomach to posterior is involuntary.
• GI tract varying considerably from spp. to spp. group.
• Nutrient absorption increased by folding and increase of
surface area (typhlosole, sprial valve).
Alimentary Canal Oddities...
• Esophagus (Peristalsis)
-one-way trip for food!
• Stomach (Killer pH!)
-Some tilipia <2! Can actually
break down plant cell walls in
absence of appropriate gastric
• No stomach (lungfish, carp)! If no stomach, then no HCl =
no shell or bone digestion.
Alimentary Canal Oddities...
• Intestine
-Pyloric caeca are
fingerlike pouches that
may aid in nutrient
GI (cont.)
• Liver-fat storage, detox., oil source.
Sharks—huge liver ~50% of gut space, but they don’t
get cancer??
• Gallbladder—source of bile (fat emulsification).
• Pancreas—source of digestive enzymes
part of liver in some fish and crustaceans (hepatopancreas)
• Fish regulate buoyancy several ways:
Low density tissue (liver in sharks)—increase fat
“Lift” from fin movement or hydrodynamics
Reduced heavy tissue (bones and muscle)
Gas (swim) bladder
Gas Bladder
• Used for buoyancy control.
Physostomas-gas bladder is connected to the stomach.
Buoyancy achieved by gulping air.
Physoclistous-not connected to stomach. Fish has
developed rete mirable and gas gland which serve
to promote gas exhange.
Smooth & Cardiac Muscles:
Circulation and the Heart
Circulatory System
double circuit
1- heart to lungs
2- heart to body
single circuit
Special conditions for
fish circulation
– Environment is oxygen poor (1-8ppm on average)
– Heart is simplest of vertebrates
– Fish have less blood volume than other vertebrates
• Adaptations by fish
– Composition of blood (many different hemoglobins)
– Morphology of circulatory apparatus
– Behavioral responses to oxygen availability (move!)
Functions of the Circulatory System
• Delivers oxygen
• Delivers nutrients
• Removes metabolic waste
• Fights pathogens
Components of the Circulatory
System to Study
• Blood
– Erythrocytes-red cells
– Leukocytes –white cells
– Structure of Hemoglobin
• Vascular system
– Heart
– Vessels
Formation of Fish Blood Cells
• Formed from hemocytoblast
• Blood forming site differs between fishes.
– Agnatha
• Mesodermal envelope around gut in hagfish
• Fatty tissue dorsal to nerve cord in lampreys
- “fat column”
– Elasmobranchs
• Leydig organ (near esophagus)
• Epigonal organ (around gonads)
• Spleen
Formation of Fish
Blood Cells continued
• Teleosts
– Kidney, Spleen, Cranium
• Fish bone has no marrow!
Leukemia an issue???
Erythrocytes-red cells
• Most abundant fish blood cells
• Nucleated
• Size range exists (elasmobranchs usually larger,
but fewer)
• More active species have more red blood cellsWhy?
Hemoglobin of Fish
• Primary means for transporting oxygen
– In some fish up to 15% may be in plasma
• A few fish have no hemoglobin (rare
situation) When does this happen?
– Environmental oxygen high
– Low metabolic requirements
Fish Hemoglobin Characteristics
• Structure is different in different fish
– Monomeric
– Single-heme peptide molecules
– Found in Agnatha
• Tetrameric
– Four peptide chains
Fish Hemoglobin Characteristics
• May differ in many features
– Composition of amino acids
– Affinity for oxygen (more on this later!)
– Some salmonids have ~18 different kinds!
Having Different Hemoglobin Types
• Different hemoglobins have different responses
- temperature
- oxygen absorption
• Allows fish to deal with changing conditions
– Important for migratory species (salmon)
• Some fish gain or lose types as they age
Blood Oxygen Affinity
• pH
– Decreasing pH decreases affinity
– Often associated with carbon dioxide
• Carbon dioxide
– Increase in CO2 drives off O2 (Bohr effect)
– Decrease in blood pH magnifies Bohr effect
Blood Oxygen Affinity
• Temperature
– Increase in temperature depresses oxygen
affinity and capacity (total amount bound)
– Results in fish having narrow temperature
Fish Circulatory System
• Primary circulation
– Closed system
• Heart
• Arteries
• Capillaries
• Veins
• Secondary circulation
– Collects blood that is outside the primary
– Originally thought to be lymphatic
• No lymph or lymph nodes.
Divisions of Primary Circulation
• Branchial circulation
– Blood from heart through gills
• Systemic circulation
– Blood from gills to body to heart
• Blood flow is continuous from heart, to lungs, to body,
back to heart
Proximity of Heart & Gills
Exceptions to Normal Circulation
• Hagfish have accessory inline hearts
• Lungfish have pulmonary circulation
• There are also many small adaptations in some species.
Structure of the Fish Heart
• Four chambered heart
• All four chambers are in line
• The heart pumps only venous blood
• Except for a few air breathing fish, all
blood is pumped to the gills
(Vascular circulation in lungfish.)
Chambers of the Fish Heart
(1) Sinus venous
– Collects blood from venous ducts
(2) Atrium
– Accelerates blood flow
(3) Ventricle
– Large muscled chamber
– Provides propulsive flow for circulation
(4) Bulbus arteriosus (bony)
Conus arteriosus
– Changes blood from a pulse to continuous
Conus vs. Bulbus Arteriosus
• Conus Arteriosus
– Contractile
– Cardiac muscle
– More than one valve
• Bulbus Arteriosus
– Elastic
– Mostly connective tissue
– One valve dividing it from ventricle
Regulation of the Fish Heart
• Self-regulating
• Timing can be modified by brain
(influence on the autonomic nervous
• Pace is set by pacemaker cells
• Many areas show pacemaker activity
The Hagfish Heart
• Most primitive
• Sinus venous well developed
– Divided into two parts to receive different
• Bulbus arteriosus
• Have 3 additional hearts
– Cardinal heart in head
– Caudal heart near end of tail
– Portal heart – pumps blood through liver
Lamprey Heart
• Largest of fish hearts
• Atrium overlies ventricle
• Bulbus arteriosus
Elasmobranch Heart
• Conus arteriosus
• Sinus venosus with almost no cardiac
• Ventricle has two muscle layers
– Compacta = compact outer layer
– Spongiosa = inner layer
Teleost Heart
• Variation exists across the group
• Sinus venosus is thick-walled
• Most have bulbus arteriosus
• Some have conus arteriosus (usually more
Lungfish Heart
• Atrium is divided into two parts by an
incomplete septum
– Functional 3 chamber heart
– Like amphibians
– Right atrium larger than left
– Right = deoxygenated from sinus venosus
– Left = oxygenated from pulmonary vein
Blood and Freezing Temp.
• Osmolality
• fp = delta freezing point
– -0.06 FW
– -0.75 SW
• Ice fishes – Nototheniidae
– glycoproteins
• Winter Flounder -- Pleuronectes
Circulatory Systems of Fishes:
• Delivery of needed substances for
metalolism to tissues where needed:
nutrients (sugars, lipids, proteins)
Functions of Circulatory System
• Delivery of waste products away from
carbon dioxide
nitrogenous wastes (NH3, NH4+, urea)
excess minerals
invading organisms (pathogens)
Functions of Circulatory System
• Maintenance of stable pH via buffer system:
– H20 + CO2 = H2CO3 = HCO3- + H+ = 2H+ +
– Last step only at pH > 10, so not in fish blood
Components of Fish Circulatory
• Blood:
– aqueous solution
– solutes (proteins, sugars, minerals)
– blood cells
• erythrocytes (red blood cells)
• leucocytes (white blood cells)
Components of Fish Circulatory
• Plumbing:
– heart
sinus venosus
bulbus (conus) arteriosus
• Blood vessels
– arteries
– veins
– capillaries
Nervous Systems of Fishes
Sensory, Motor and Integrative
Organization of the brain
(anterior to posterior)
• Telencephalon (forebrain):
– olfactory sensation
– coordination of smelldriven activities
– receives visual and
mechanical information,
• Diencephalon:
– homeostasis
– pineal organ (gland)
– light sensitive
– endocrine functions
Brain Organization
(anterior to posterior)
• Mesencephalon (mid-brain):
– Optic tectum (dorsal
portion of mesencephalon):
• receives visual input
(optic nerve)
• central processing
• coordinates visual input
with other sensory
• sends out motor signals
to musculature, e.g.
escape response from
sight of predator
Brain (cont.)
• Metencephalon
– coordinates
swimming activity
– coordinates:
• balance input
with motor
• electrical sense
input with
Organization of the brain
(anterior to posterior)
• Myelencephalon (medulla
– relay system for the senses
– receives sensory input from
cranial nerves 3 - 12:
• acoustic
• tactile
• taste
• lateral line
• electrical (some)