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Normal Salmonid Histology

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					                         Normal Salmonid Histology
                          Selected Organs/Tissues

                 Diane G. Elliott, Western Fisheries Research Center




                       Scale


                                                                                        Epidermis

                                                                                        Dermis




                                                  Myoseptum
                                                                                        Skeletal
                                                                                        muscle




Low magnification view of normal skin (scaled region of body, cross section) and
skeletal muscle of a juvenile chinook salmon Oncorhynchus tshawytscha. The skin is an
important first line of defense against pathogens. Note that the scales are located in the
dermis; for scale loss to occur, the epidermis must be torn. The epidermis is normally
covered by an acellular mucous secretion (cuticle) that is constantly sloughed and
renewed; the cuticle is usually lost during histological processing. Hematoxylin and eosin
stain (H&E). Magnification 100.
                                                   Epithelial cell

             Mucous cell

                                                                                              Epidermis



        Scale
                                            Stratum spongiosum (dermis)
                                                                                              Dermis



                                    Stratum compactum (dermis)

             Melanophore

                                                                                              Skeletal
                                              Muscle fiber                                    muscle
              Hypodermis



Higher magnification view of normal skin (epidermis and dermis) and skeletal muscle of
a juvenile chinook salmon. Keratinization of the epidermis to produce the horny surface
layers characteristic of land vertebrates is rare among fishes; fish epidermis is generally
metabolically active throughout all its layers. The bulk of the dermis is made up of
fibrous connective tissue, and also contains blood vessels, nerves, scales, and adipose
(fat) tissue (in hypodermis). Skeletal muscle fibers are very large cells with multiple
peripherally located nuclei. H&E stain. Magnification 200.
                                                   Filament




                                   Lamella




Low magnification view of a portion of a gill arch of a rainbow trout Oncorhynchus
mykiss showing parts of two filaments (primary lamellae) supporting numerous lamellae
(secondary lamellae). The filaments are sectioned longitudinally through the cartilaginous
supporting rods. H&E stain. Magnification 100.
                                                                       Epithelial
                                                                       cells




    Filament
    cartilage                           Chloride
                                        cell

                                                                      Pillar cell




                                   Erythrocyte




Higher magnification view of a portion of a normal gill filament of a rainbow trout. In
longitudinal section, the gill lamella is comprised of two layers of epithelial cells that
cover a planar sheet of pillar (pilaster) cells. Cytoplasmic extensions (flanges) between
adjacent pillar cells form the vascular space occupied by erythrocytes (red blood cells) ,
which have highly eosinophilic (pink) cytoplasm. Chloride cells or ionocytes are
common at the bases of lamellae and are involved in ion regulation. H&E stain.
Magnification 320.



Normal heart of a sockeye salmon Oncorhynchus nerka. H&E Stain. Blood flows
sequentially through the sinus venosus (not shown), the atrium, the ventricle, and the
                                         Atrium
bulbus arteriosus. The thin-walled atrium and thick-walled ventricle are comprised in part
of cardiac muscle, whereas the walls of the bulbus arteriosus are made up of elastic
connective tissue and smooth muscle. H&E stain. Magnification 50.

                               Valves



                                                                             Bulbus
                                              Valves                         arteriosus




                           Ventricle
Normal cardiac muscle of the ventricle of a sockeye salmon. Cardiac muscle fibers differ
from skeletal muscle fibers in that they are branched and the nuclei are centrally located.
H&E stain. Magnification 400.
                         Artery

                                                             Melano-
                                                             macrophages




    Glomerulus                                                         Hematopoietic
                                                                       (interstitial)
                         Renal                                         tissue
                         tubules




Fish kidneys are among the least readily recognized of fish organs because of their lack
of gross structural similarity to mammalian kidneys. However, nephrons similar to those
of higher vertebrates are present in the majority of fish kidneys. The photo shows a
portion of the posterior (renal) kidney of a rainbow trout. Urinary elements are embedded
in hematopoietic tissue. H&E stain. Magnification 200.
   Melano-
   macrophages



                                                          Vein




                                                Erythrocytes                                 Hematopoietic
                                                                                             tissue




                                                Leukocytes




Portion of the anterior kidney (also called the pronephros or head kidney) of a rainbow
trout. The anterior kidney contains hematopoietic (blood cell forming) tissue but no renal
elements. A large vein containing erythrocytes (red blood cells) and leukocytes (white
blood cells) is visible; veins are distinguished from arteries (see posterior kidney) by
thinner walls with fewer smooth muscle and elastic components. H&E stain.
Magnification 200.
Splenic                                                                                 Melano-
capsule                                                                                 macrophages




                                                                                       Red pulp



    White pulp




          Spleen of a juvenile rainbow trout showing the nodular arrangement of the germinal
          nodes (white pulp) and stroma of connective tissue with red blood cells (red pulp). This
          nodular arrangement is less pronounced in some salmonids. The splenic capsule is much
          thinner than in mammals. H&E stain. Magnification 50.
                                                                                           White pulp




                                                                                           Red pulp




Higher magnification view of a portion of the spleen of a rainbow trout. The spleen
functions in hematopoiesis and red blood cell storage as well as blood cell destruction,
and may have immunological functions similar to lymph nodes in mammals. H&E stain.
Magnification 100.
                                                                 Bile duct



               Melano-
               macrophages


                                                                     Hepatocytes




Low magnification view of normal liver tissue of a rainbow trout. The appearance of the
hepatocytes can vary widely with such factors as season, nutritional status, age, and sex.
The hepatocytes in this fish are largely devoid of cytoplasmic glycogen vacuoles. H&E
stain. Magnification 200.
                                                      Bile duct




                                                                         Hepatocytes




        Melano-                                        Arteriole
        macrophages




Upper photo: Higher magnification view of normal liver tissue of a rainbow trout. Note
that the hepatocytes are arranged in laminae or cords two cells thick; the sinusoids
between the cords are lined with endothelial cells. Lower photo: Liver of another rainbow
trout showing hepatocytes with abundant glycogen vacuoles in the cytoplasm. H&E stain.
Magnification 400.
                                           Gastric
                                           glands                      Feed in
                                                                       lumen




                                                               Gastric
                                                               epithelium




                                           Muscle




Longitudinal section of a normal cardiac (anterior) stomach of a sockeye salmon. All
regions of the stomach have a thick wall of longitudinal and circular muscle, and this
region of the stomach has gastric glands, which open into gastric pits. Note the feed in the
lumen of the stomach. H&E stain. Magnification 100.
                                                              Ascending
                                                              intestine




                                                                       Pyloric caeca



             Exocrine
             pancreas


Portion of the ascending intestine and pyloric caeca of a sockeye salmon. The pyloric
caeca are extensions of the ascending intestine. Diffuse exocrine pancreatic tissue is
visible between the caeca. H&E stain. Magnification 50.
                                                                                        Exocrine
                                                                                        pancreas


                                         Epithelium       Mucous
                                                          (goblet)
                                                          cell


                                Wandering                                               Lamina
                                lymphocyte                                              propria




                                                                           Muscle




Cross section of a pyloric caecum of a sockeye salmon. The intestine, including the
pyloric caeca, has a much thinner muscular wall than the stomach. The columnar
epithelium includes mucous (goblet) cells and wandering lymphocytes. The lamina
propria is a connective tissue layer beneath the epithelium. H&E stain. Magnification
200.
                                       Endocrine
      Exocrine                         pancreas
      pancreas




                 Salmonid pancreatic tissue (H&E stain).
                 Top photo: Exocrine (acinar) and
Zymogen          endocrine (islets of Langerhans)
granules         pancreatic tissue of a sockeye salmon. In
                 salmonids, pancreatic tissue is dispersed
                 throughout the adipose tissue that
                 surrounds the pyloric caeca, but in other
                 other teleosts, exocrine pancreatic tissue
                 may be found in locations such as the liver
                 (hepatopancreas) or spleen. Magnification
                 200. Left photo: Eosinophilic-staining
                 zymogen (proenzyme) granules in
                 basophilic-staining pancreatic acinar cells
                 of a rainbow trout. The exocrine pancreas
                 produces digestive enzymes.
                 Magnification 400.

				
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posted:12/4/2011
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