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Anatomy and Physiology

III. Anatomy and Physiology

Figure 5 - Nomenclature of some external features (fins)

Figure 6 - Schematic view of gills and internal organs

A specialized structure is the gas (swim) bladder - specialized for buoyancy adjustment, it may be connected to esophagus. Also, it may have a "gas" gland which enables release or resorption of gas from blood to and from the gas bladder.

Anatomy and Physiology by System

A. Integument

1. skin

a. Outermost layer is a mucous (cuticle) layer composed of mucus, muco/polysaccharides and immunoglobulins.
b. Epidermis (malpighian cells throughout epidermis retain capacity for for cell division)
c. Dermis
d. Scales (calcified plates originating in the dermis and covered by the epidermis)

Figure 7 - Schematic view of skin of fish


B. Respiratory

1. operculum (structure which covers the gills)
2. gills

a. (There is a set of 4 gill arches on each side of teleosts) 1° & 2° lamellae on each gill arch

The thin epithelial layer lining the filamentous gill structures is very thin and allows gas exchange to occur here.

Figure 8
Figure 9
Schematic view of histologic features of gill arches in relation to water flow (after Reinert, 1992)

Figure 10 - Gill filaments of bluegill illustrating primary and secondary lamellae. H&E 16X

The gills also regulate exchange between salt and water and have a major role in the excretion of nitrogenous waste products.

C. Musculoskeletal

1.   muscle (myomeres)
    Types: Red (slow, cruising)
    White (strenous bursts of swimming, rapid fatigue)
2.   bone can be cellular or acellular in teleosts
3.   cartilage

Figure 11

Figure 12 - Transverse section through caudal portion of body (posterior to body cavity). Note vertebral column with caudal vein ventral to column. Note red and white muscle. Figure 13 - Cellular bone. Note periosteum, osteocytes, blood vessel and adjacent cartilage. H&E, 67X

D. Cardiovascular

1. heart (sinus venosis, one atrium, one ventricle and elastic bulbus arteriosis,
2. circulation - blood flows from the heart to the ventral aorta to the afferent branchial arteries to the gills for oxygenation and progresses via the efferent arteries to the dorsal aorta.

Figure 14 - Fish have a "2 chambered" heart; one atrium and one ventricle, located within a pericardial sac.

E. Digestive

1. stomach (carnivorous fish have a short digestive tract when compared with herbivorous fish.)
2. pyloric ceca (blind-ended finger-like projections extending outward from pyloric valve region)
3. intestine (not possible to divide the intestine into large and small intestine)
4. liver with gall bladder (doesn't have the typical lobular architecture that is present in mammals. There are no phagocytic (Kupffer cells) in the liver.
5. pancreas (may be interspersed with mesentery of pyloric ceca or along portal veins of liver)


Figure 15 - Schematic ventral view of digestive tract

Figure 16 - Stomach with numerous pyloric ceca leading to their opening into the pyloric region. Figure 17 - Vacuolated hepatocytes secondary to metabolic stress or disturbances.


F. Hemic

1. hematopoiesis, occurs especially spleen, kidney

(hematopoietic activity is not found in medullary cavity of bones)

2. Blood cells erythrocytes have nuclei. Fish have thrombocytes (no platelets)


Figure 18 Figure 19
Schematic view of location of hematopoietic organs in fish

G. Lymphoreticular

Fish have a thymus. They have lymphoid tissue but no lymph nodes.
1. phagocytosis
2. cell mediated response
3. humoral antibody (IgM) response 
H. Urinary

1. kidneys - A primary function of the kidney is osmoregulation. In fresh water the kidney saves ions and excretes water. In saltwater fish, the kidney excretes ions and conserves water. The majority of nitrogenous waste is excreted through the gills. The "head" kidney (most cranial portion) contains predominantly hematopoietic and lymphoid tissue; the posterior kidney contains the excretory tissue with some hematopoietic and lymphoid tissue.


Figure 20 - Kidney, posterior excretory portion, 10X

I. Reproductive
1. ovaries
2. testes 

Figure 21 Figure 22
Reproductive organs of female showing common pattern in teleosts (left) and pattern seen in salmonids (right)
(after Hoar, 1969)
Figure 23 - Reproductive organs of male (after Hoar, 1969)

Figure 24 - Gross view of ovary showing multiple large eggs. Figure 25 - Ovary with eggs in varying stages of development H&E 16X Figure 26 - Ovary with several eggs, including one undergoing dissolution. H&E 67X

 J. Endocrine

1. Adrenal Gland - The adrenal cortical tissue is represented by the interrenal cells. The adrenal medullary cells may vary is location.

2. Thyroid Gland - Thyroid follicles are very similar to mammalian thyroid tissue. Thyroid follicles are widely distributed throughout the viscera.

3. Pancreas - Islets of Langerhans may be grossly visible.


Figure 27 - An overview of the location of various endocrine glands is shown below. (after Bond, 1979)

4. Corpuscles of Stannius (located in kidney) - Secrete hypocalcin which acts with calcitonin to regulate calcium metabolism (the parathyroid glands are absent in fish).

K. Nervous

1.   brain
    cranial nerves (ten)
2.   spinal cord 

L. Organs of special sense  

 Figure 28 - Semicircular canals and membranous labyrinth

Figure 29 - Schematic view showing function of lateral line

In the lateral line, neuromasts (sensory cells) act as mechanoreceptors within the canal and relay information to the brain. There are tiny pores which provide a passage from the outside environment to the canal).