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Fish 424-Laboratory
Spring 2010
General Anatomy & Physiology of Salmonids
I.
Definition of terms:
anterior (cranial)
posterior (caudal)
cranial
caudal
dorsal
ventral
medial
distal
proximal
II.
toward the head
toward the tail
pertaining to the head region
pertaining to the tail region
toward the back of the animal
toward the belly of the animal
toward the median line
away from the center or origin
toward the center or origin
External Anatomy of fish
A.
The body is divided into head, trunk, and tail. Thick set in middle and
tapering at each end and compressed laterally which is typical of most
aquatic animals.
B.
Scales on trunk and tail are arranged in diagonal rows overlapping each
other similar to shingles on a roof.
 Covered part of scales which contain the growth rings.
 Scales set in pockets in the deeper part of the skin (dermis), and are
covered by the superficial layer of the skin (epidermis).
 Head is covered by epidermis and some scales.
C.
Lateral line is present along middle side of body.
 A tube filled with mucus connected to exterior by numerous pores and
underlain with nerve connecting to brain.
D.
Head
 Terminal mouth bounded by well-defined jaws (maxillary and
dentary).
 Nares: located on dorsal side of the anterior end of head. Each nare is
divided into two portions, which permits water to circulate through
the olfactory sac.
 Eyes: located in lateral position at anterior end of head.
 Ears have no external openings, but are located just posterior to eye.
 Operculum
 Located at the posterior and lateral positions of the head.
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E.
Fins
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F.
III.
Branchiostegals
Attached to the ventral portion of the operculum is the branchiostegal
membrane supported by several bony rays (the branchiostegals).
Gill arch
o Beneath the operculum are located four pair of gill arches.
o Each arch bears a gill on its outer surface.
o Each gill consists of two rows of filaments.
o Each filament consists of numerous lamellae.
o Inner margin of arch bears a single row of tooth-like
projections the gill rakers.
Respiratory movement
o Mouth opens, opercula move outward, branchiostegal
membrane unfolds and closes gill opening, water is thus drawn
into the mouth and bathes the gills.
o To exhale the mouth is closed by means of oral valve or
membranous flap which seals opening, the opercula move
inward, the branchiostegal membrane folds up and the water
passes out through the gill slits and gill opening.
Median fins dorsal, adipose, caudal, and anal.
Paired fins are the pectoral and pelvic.
Paired fins supported by pectoral and pelvic girdles which consist of
bone and cartilage.
Dorsal and anal fins supported by pterygophores, caudal fin
supported by spinous processes of the vertebra (hypural plate) into
which the actinotrichia extend. Salmonidae have typical homocercal
tail.
Openings.
 The anus is on the median ventral line posterior to the ventral fins. It
is the posterior opening of the digestive tract.
 Posterior to the anus is the genital pore or papilla.
 Posterior to the genital pore is the urinary pore, the excretory duct
from the kidney.
Sensory perception of the fish.
A.
Sight
 The eye is the organ of sight
 Sight is the predominant sense of salmon. In teleostean fish the optic
lobe is the predominant part of the brain.
B.
Hearing
 Lateral line perceives sounds of low wave length.
 Ear perceived sounds of higher wave length.
IV.
C.
Equilibrium
 Organs of equilibrium are the lateral line and the ear.
D.
Touch
 Sense organs of touch scattered throughout the body of the fish also
contained in the lateral line.
E.
Smell
 Long range perception of chemicals
 Preceptors of smell through olfactory sac
F.
Taste
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G.
Kinesthetic perception
 The perception of movement and position
 Function of lateral line
H.
Temperature
 Function of lateral line
Taste is the perception of chemicals upon contact.
Taste buds must have much stronger stimuli than those of smell.
Taste buds located on tongue and head.
Fish distinguish sour, salt, and bitter.
Functions of various sense organs
A.
B.
C.
D.
Eye
 Sight
Ear
 Equilibrium and hearing
Nares
 Smell
Lateral line
 Hearing, equilibrium, touch, perception, and temperature
V. Internal Anatomy
A.
The internal anatomy of the salmonidae may be reduced to eight different
systems each serving a different function. This section will be concerned
with the structure and function of the skeletal, muscular, digestive,
respiratory, circulatory, and excretory systems. The reproductive system
will be presented in a later section. The main functions of the nervous
systems were presented in the previous sections.
B.
The skeletal system consists of the axial, visceral, and appendicular divisions.
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Supporting tissues.
o The supporting tissues consist of connective tissue which are
referred to as ligaments, tendons, septa, fascia, and
mesenteries.
o Ligaments are tough bands of tissue between bones.
o Tendons are thick narrow bands by which muscles are
attached to the skeleton.
o Septa are heavy tissues which separate various portions of the
body.
o Fascia is the thin sheets of connective tissue which surround
muscles.
o Mesenteries are delicate tissues which support the organs of
the body cavity.
(1)
Dorsal mesenteries
o Anterior mesentery supports cardiac division of
the stomach.
o Intestinal mesentery supports intestine
throughout entire length.
(2)
Ventral mesentery.
o Attached to ventral surface of intestine at the
posterior end of body cavity
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The visceral skeleton consists of the upper and lower jaw, the
opercula, and the brachial arches which support the gills.
The appendicular skeleton includes the pectoral and pelvic girdle,
pterygophores and fin rays (actinotrichia).
The function of the skeletal system is one of support.
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VI.
Skeletal tissues: the important skeletal and supporting tissues of the
salmon are connective tissue, cartilage, and bone.
Axial skeleton
o The axial skeleton is divided into head, trunk, and tail regions.
o The skeleton of the head consists of ossified bones composing
the skull.
o The trunk skeleton consists of a modified portion of the
vertebral column.
o The tail skeleton consists of the remainder of the vertebral
column and the hypural plate.
o The vertebrae in salmonidae are amphicoelus or biconcave
Muscular system
A.
There are three types of muscle tissue: smooth, striated, and cardiac.
 Smooth and cardiac muscles are involuntary.
 Striated muscle is voluntary
VII.
B.
Striated or voluntary muscle is divided according to its relation to the
skeleton into axial, appendicular and visceral.
 Axial muscles
o Axial muscles are segmentally arranged into myomeres and
separated from one another by septa.
o Septa, also, divided groups of muscles at the lateral line and the
dorsal and ventral median lines.
 Appendicular and visceral muscles
o Appendicular and visceral muscles are individual musculus
composed of a definite mass of muscle tissue surrounded by
connective tissue (fascia).
o Appendicular muscles move fins.
o Visceral muscles move lower jaw and gills.
C.
Smooth or involuntary muscles are found in various organs of the body in
association with other kind of tissue capable of relatively slow and limited
contraction such as the rhythmic contraction of the intestine.
D.
Cardiac muscle is striated but involuntary.
E.
Function of muscles is motion and locomotion.
Digestive system
A.
The digestive system consists of the mouth, pharynx, esophagus, stomach,
small intestine, pyloric cecae, liver and pancreas.
 The mouth serves as a grasping organ; the teeth function for the
retention of prey.
 Pharynx, which leads to the esophagus, is a continuation of the mouth
cavity and is also concerned with respiration.
 The esophagus is a muscular tube leading from the pharynx to the
stomach.
 The stomach consists of two parts: the cardiac and the pyloric
portions. At the end of the pyloric section is a heavy muscle, the
pyloric sphincter, which controls the flow of food out of the stomach
and into the intestine.
 The intestine is divided into three parts: the duodenum, and small
and large intestines.
o Duodenum: short portion of the intestine to which the pyloric
cecae are attached and which receives the bile duct and the
pancreatic duct
(1)
Pyloric cecae serve to increase the absorption space of
the intestine.
o The small intestine is the predominant portion of the intestinal
tract.
o The large intestine is extremely short and is located just
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B.
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anterior to the anus.
o Salmon and trout have the extremely short digestive tract
typical of carnivores.
Digestive glands in the salmon and trout include the gastric and intestinal
glands, the liver, and the pancreas.
o The gastric glands are located in the lining of the stomach.
o The intestinal glands are located in the lining of the small intestine.
o The liver is a bi-lobed organ located in the anterior and left lateral
portion of the body cavity.
(1)
The gall bladder is a thin-walled sac embedded in the
liver and serves as a storage reservoir for the bile which
is secreted by the liver.
(2)
The bile duct leads from the gall bladder into the
intestinal tract at the duodenum.
o The pancreas is a diffuse gland located on the pyloric caeca.
(1)
The pancreatic duct discharges into the intestine in the
duodenal region.
Function of the digestive system.
The digestive system is the system concerned with the intake of food, its
mechanical and chemical preparation for assimilation, and the elimination of
the remaining waste material.
The mouth in fishes is concerned primarily with the seizing of food. As there
are no digestive glands in the mouth, its function is purely mechanical.
The esophagus also functions chiefly in a mechanical manner. Its rhythmic
contractions force the food into the stomach.
The stomach has three functions: those of storage, mechanical mixing, and
chemical modification.
o The ability to store food makes continuous feeding
unnecessary.
o Mechanically, the food is thoroughly churned and mixed by the
action of the muscular walls of the stomach.
o Chemically the food is acidified by the secretion of
hydrochloric acid and certain proteins are partially digested by
the secretion of enzymes from the gastric glands.
When the acid stomach contents are ejected through the pyloric sphincter,
the acid acts upon a substance in the lining of the duodenum and
changes this substance to secretin. The secretin is absorbed by the
blood and carried to the liver and pancreas which are stimulated to
secrete their fluids. Secretin belongs to a class of activators known as
hormones.
The pancreatic juice contains three enzymes which act upon proteins,
carbohydrates, and fats.
Bile, the secretion from the liver, contains no enzymes but does contain
water, bile salts, and certain excretory products.
o Bile salts break up the fats into very fine droplets so that the fat-
IV.
splitting enzymes may act upon them more readily.
 In the small intestine the final phases of digestion take place.
o The intestinal bands secrete enzymes which act on proteins and
carbohydrates.
 Absorption takes in the small intestine.
o The enzymes break down complex proteins into amino acids and
complex carbohydrates into simple sugars.
o The simple sugars and amino acids are absorbed directly into the
blood.
o Glycerol and fatty acids are absorbed but in the process are at least
partially reconverted into fats.
o As fats are insoluble they exist in the form of droplets and are
delivered not the blood but to the lymph system. However, the
lymph returns to the blood stream and the entrance of fats into
the blood stream is merely delayed.
Respiratory system
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V.
The respiratory system of salmonidae consists of the gills.
o The morphology and the mechanics of breathing have been described
in a previous lecture.
The air bladder of salmon and trout is included in the respiratory system but
does not function as a respiratory organ in the salmonidae.
o The air bladder in salmonids functions as a hydrostatic organ.
o During the fry and early fingerling stages of development the air
bladder is connected by a duct to the esophagus which may explain
why fry when placed in troughs come to the surface to feed.
The function of the respiratory system is the exchange of gases.
o Oxygen is absorbed through the gills into the blood; ammonia (NH4+)
and carbon dioxide are transferred from the blood into the water.
o This exchange of gases is accomplished by differences in pressure
gradient. It differs from osmosis in that it is a flow from the dense to
the less dense.
Circulatory system
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The circulatory system consists of the blood, a definite network of closed
vessels through which it flows, and the lymph and its less definite system of
vessels.
o The blood is a fluid tissue consisting of the liquid plasma and cellular
components, the red and white corpuscles.
 The plasma consists of about 80% water in which are dissolved
the proteins and carbohydrates; the waste materials such as
urea and uric acid; mineral salts; secretions of the ductless
glands; and antibodies.
 The blood cells are of two main types, the red cells or
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erythrocytes and the white cells or leukocytes.
(1)
The erythrocytes are typically flattened, nucleated cells
which contain hemoglobin. The hemoglobin has the
property of combining readily with oxygen and serves
to transport oxygen to the cells of the body.
(2)
The leukocytes of which there are three types aid in the
removal of broken down tissue and the destruction of
harmful bacteria.
 Certain leukocytes have the ability to move
through the capillary walls and into the intercellular spaces from which they are picked up by
the lymphatic system.
(3)
Thrombocytes are also present in the blood and aid in
the formation of blood clots.
The closed system of vessels through which the blood circulates
includes the heart, arteries, veins, and capillaries.
o The heart of a fish consists of two chambers, the auricle and
ventricle.
o The blood is pumped from the heart into the ventral aorta from
which it enters afferent brachial arteries and then to the
capillary network in the gill lamellar. The aerated blood from
the gills is collected via the efferent brachial arteries in the
dorsal aorta from which it is delivered by a series of branches
to all parts of the body. These branches continue to divide
until they form minute thin-walled capillaries where oxygen
and food nutrients of the blood are transferred to individual
cells. The de-aerated blood of the capillaries is collected into
larger branches, the veins, from which it is returned to the
heart.
 Portions of the venous blood are diverted through the
hepatic portal (liver) and renal portal (kidney) systems.
Lymph is derived from the portions of the blood which pass through
the walls of the capillaries. It consists of plasma and leukocytes and is
very little different from blood minus its red corpuscles. It occupies
the spaces between the cells of the body.
The lymphatic system starts in the intercellular spaces which
eventually empty into some vein.
o Along the course of the lymphatic system are solid glandular
bodies known as lymph nodes.
o The spleen is also an organ associated with the lymphatic
system.
o Associated with small intestine are the lacteals which originate
in its walls and extend into minute finger-like projections of
the intestine for the absorption of fat. The lacteals lead into the
lymphatic system.
VI.
B.
The blood producing organs of the body consist of the anterior portion of the
kidney, the spleen, thymus gland, and the lymph nodes.
 The anterior portion of the kidney functions as does the bone marrow
in higher animals in the production of red cells.
 The spleen, lymph nodes, and thymus gland produce leukocytes.
 The spleen also serves as a place for storage of red blood cells.
C.
The functions of the circulatory system may be summarized as follows:
 The distribution of food material by leukocytes and lymph from the
digestive tract to the tissue cells.
 The distribution of oxygen by the erythrocytes from the respiratory
membranes to the tissue cells.
 Transportation by the lymph and blood of waste products of
metabolism from the cells to the organs of excretion.
 The distribution of chemical substances (hormones) from the ductless
glands to all parts of the body.
 The equalization of body temperature resulting from the oxidation of
tissues.
 Defense against harmful organisms by the leukocytes and by
formation within the blood of antibodies.
The Excretory System
A.
The excretory system is concerned with the removal of the waste products of
metabolism, which consist of carbon dioxide, water, and nitrogen-containing
substances. The organs of excretion are the gills, spleen, liver, and kidney.
 The gills, as mentioned previously, are concerned with the
interchange of gases. In this process carbon dioxide and ammonia are
eliminated from the blood.
 Among other functions of the spleen is the destruction of worn out red
cells. The hemoglobin from these worn out cells is forwarded through
the blood stream to the liver and the iron is returned to the kidney.
All venous blood from the spleen passes through the hepatic portal
system of the liver.
 In the liver the hemoglobin of the worn out blood cells is converted to
bile salts and is excreted through the gall bladder and bile duct into
the intestine. Apparently the liver supplements the spleen in the
breakdown of the red cells.
o Another excretory function of the liver is the conversion of
ammonium salts into urea which is carried in the blood to the
kidneys for excretion.
 The kidney is the principal organ of excretion.
o In salmon the posterior portion functions in an excretory
capacity and the organ which is usually paired is fused into
one.
o In the kidney the venous system is broken down into the
minute capillaries of the renal portal system.
o The functional unit of the kidney is the nephron. This is
essentially a coiled tubule with the closed end in close relation
to a blood vessel and the other leading to the excretory duct.
o Other nitrogenous substances, salts, and water are removed
from the blood by the kidney and excreted through the urinary
duct to the outside by means of the urinary pore.
VII.
The Ductless Glands
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The ductless or endocrine glands play an important part in regulating the
various life processes by chemical means. Their secretions, the hormones,
are built up from materials brought to them by the blood stream and are
distributed by the blood stream throughout the body.
o Hormones are the secretions of the endocrine glands which stimulate
activity in an organ. They are catalytic in nature, i.e., they stimulate a
reaction but are not consumed by the reaction.
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The pituitary gland is located on the ventral surface of the brain midway
between the brain and the roof of the mouth. Its function is to raise the sugar
level of the blood, regulate growth, and to control the development of the sex
organs.
o Extract of pituitary gland has been used with some success to cause
sexual maturation of fish.
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The pineal body is located on the dorsal surface of the brain. Its exact
purpose is not known but it is suspected to have endocrine and
geopositioning functions.
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The thyroid gland occurs in scattered patches of tissue in the region of the
ventral aorta. It is concerned with metabolism, growth, and sexual
development.
o A deficiency in iodine causes an upset in the thyroid function and
goiter may develop. This condition is an enlargement of the gland
itself and has been known to occur in trout.
o Over secretion by the thyroid gland greatly increases the rate of
metabolism, causes loss of weight, rapid respiration, protruding
eyeballs, and extreme nervousness. This condition is associated also
with increase in gland size and described as exophthalmic goiter.
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Parathyroid glands may or may not be present. If present in fishes, they occur as
very diffuse glands in the same region as the thyroids. They are concerned with
calcium metabolism.
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The thymus gland is in the pharynx dorsal to the brachial arches. In addition to
production of special lymphocytes it is believed to be concerned with the immune
response. This gland does not function after maturity is reached.
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Chromaffin bodies are located in the anterior portion of the kidney. They secrete
adrenalin which causes a rise in blood pressure and an increase in the sugar content
of the blood.
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The interrenals occur in the median portion of the kidney.
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The pancreas besides producing the digestive enzymes also produces a hormone,
insulin, which aids in the utilization of sugar. This hormone is produced in a
separate but diffuse portion of the gland which contains the Islets of Langerhans.
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The lining of the duodenum contains the hormone secretin which stimulates the
secretion of the bile and pancreatic juices.
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In addition to the development of the germ cells, the gonad or reproductive
produced secretions which cause the development of the secondary sexual
characteristics of the male and female. These characteristics are very pronounced in
fishes at spawning time.
VIII.
Function of various internal organs of the body which may be observed in a gross
dissection:
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The most prominent organ of the body cavity is the liver. The liver is
concerned with detoxification, digestion, excretion and hematopoiesis.
o In digestion, the liver secretes the bile salts.
o The liver serves in an excretory capacity by the destruction of worn
out red blood cells and the conversion of the hemoglobin into bile
salts for excretion and the alteration of ammonium salts into urea.
o Another function not previously mentioned is that it also serves for
storage of glycogen or animal starch.
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After removal of the liver, the gastro-intestinal tract is fully exposed.
o Cardiac and pyloric portions of the stomach function to acidity the
food and perform preliminary digestive processes on proteins, to
agitate the food, and to serve as a storage compartment.
 Note the anterior mesentery and the attachment of the pyloric
to the cardiac portion of the stomach by filamentous bands.
o The pyloric sphincter controls the movement of food out of the
stomach.
o The duodenum contains the gland which secretes the hormone
secretion, the openings of the bile and pancreatic ducts and is the
place of attachment of the pyloric cecae.
o The pyloric cecae serve to increase the absorption space of the
intestine.
o The small intestine functions in the digestion and absorption of food.
Enzymes are secreted by glands of the small intestine which
break down proteins and carbohydrates.
 Carbohydrates and proteins are absorbed directly into the
blood stream and fats through the lacteals of the lymphatic
system.
 Note the intestinal and ventral mesenteries.
o The large intestine serves as storage space for the accumulation of
waste before excretion.
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Other organs of the body usually have multiple functions.
o The pancreas serves for the production of the digestive juices and
insulin for the control of blood sugars.
o The spleen produces leukocytes, serves as a storage space for red
blood cells, and destroys worn out red blood cells.
o The kidney is divided into two parts. The anterior portion produces
red and white blood cells and the posterior serves as the principal
organ of excretion.
o The swim bladder is a hydrostatic organ.
o The heart serves to move the blood through the circulatory system.