Download SHARK DISSECTION

SHARK DISSECTION
It will be beneficial to watch the short video clips on the link below:
http://www.amnh.org/learn/pd/sharks_rays/rfl_dissection/index.html
INTRODUCTION:
The Dogfish shark is a good example of a primitive, jawed fish. Unlike most sharks, the
dogfish prefers the colder waters of the North Atlantic and North Pacific oceans. They are
small sharks, ranging in size from one-half meter to one meter in length. Adult females are
slightly larger than the males. The shark exhibits all the internal characteristics of vertebrates,
such as a closed circulatory system, a large coelom, and an endoskeleton. The major difference
between the shark and other vertebrates is the shark's atypical skeletal system that is comprised
entirely of cartilage
PRE-LAB: Define the function of the following: (If you have trouble finding the function of a
structure, Google it!)
1. Lateral line
2. Rostrum
3. Spiracle
4. Nare/external nostrils
5. Ampullae of Lorenzini
6. Claspers
7. Cloacal opening
8. Myomeres
CLASSIFICATION: Fill in the missing parts in your lab book
Kingdom: Animalia
Phylum:
Class: Chondrichthyes
Order:
Family: Squalidae
Genus: Squalus
Species:
Scientific Name:
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Sketch #1: Draw a picture of your shark dorsal side up. Label: posterior dorsal fin, eyes,
mouth, snout and nostrils. (Drawing should be ½ page of your lab book)
PROCEDURES:
External Dissection:
1) Prepare a place for your shark by making a 'shark nest'. Flatten a large plastic bag on
your work area and then place several sheets of newspaper on top of the bag to absorb
any fluid from the shark or the container.
2) Examine the skin of the shark by running your fingers over it lightly, from the posterior
to the anterior end. The roughness you feel is the placoid scales, also called the dermal
denticles. Use a scalpel to remove a small sample of skin and then place this sample
under a hand lens. Because of its abrasive quality, shark skin was once known as
"shagreen" and was used to polish wood.
3) Locate the mouth, eyes, nostrils (external nares), snout, and olfactory sacs (inside each
spiracle). The spiracles are actually reduced, modified gills. Most fish respire by taking
in water through the mouth and sending it through the pharynx to the gills. However,
when a spiracle is present, water enters through it also. Relatives of the shark, such as
rays and skates, which live on the bottom of the ocean, use the spiracle for water intake
almost exclusively.
4) The body is divided into three sections, the head, trunk, and the tail.
5) Locate the lateral line and notice that the body is darker above the lateral line than below.
This special type of shading works to camouflage the shark as the natural light from
above highlights its dorsal side and makes shadows on the ventral side. What is the
function of the lateral line?
6) Locate the seven fins on your shark: anterior dorsal, pectoral (2), pelvic (2), caudal, and
posterior dorsal. Notice that the caudal fin is asymmetrical. This improves the shark's
stability, allowing it to ride evenly through the water. In fish more advanced than the
shark that have lungs or a swim bladder, this extra stability is unnecessary. Therefore,
such fish have a symmetrical caudal fin.
7) Open the mouth and describe the teeth.
8) Identify the gills and describe them. What is the function of the gills?
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9) Determine the sex of your shark by checking the pelvic fins for claspers. Only males
have these strong, grooved structures. They are used during mating to hold the female
stationary. Make sure you observe a shark of each sex. Locate the urinary ducts and in
the male, the genital ducts that open at the tip of the urinary papilla. This can be found
just inside the cloaca, the common chamber on the ventral side of the shark, between the
two pelvic fins. The cloaca serves as an exterior opening for the digestive, excretory, and
reproductive systems.
Write down the Gender of your shark next to your drawing.
Internal Dissection:
1) Place the shark on the prepared surface, ventral side up. Using the diagram as a guide,
take a scalpel and begin cutting just anterior to the pelvic fins, making the cut on the right
side of the midventral line. Continue cutting anteriorly until you reach the pectoral fins.
Make two transverse cuts, across the body, one just posterior to the pectoral fins and
another just anterior to the pelvic fins. The cuts should extend from one lateral line of the
shark to the other.
2) Carefully examine the layers of the body wall and locate the following structures:
connective tissue, muscle tissue, and epithelium, and the lining of the pleuroperitoneal
cavity.
3) Digestive System:
a) At the most anterior part of the pleuroperitoneal cavity rests the liver. Count the
lobes of the liver and record. What is the function of liver?
b) The long thin gall bladder is imbedded in the median lobe of the liver. To observe it
better, scrape away the liver tissue with a dissecting probe. Once the gall bladder is
exposed, locate the attached bile duct. What is the function of the gall bladder?
c) Spread the lobes of the liver to locate the esophagus and the stomach. Both have
approximately the same diameter so it is difficult to tell where the esophagus stops
and the stomach begins. The posterior end of the stomach curves anteriorly, giving
the stomach a "J" shape. The rest of the digestive system turns posteriorly to form a
straight intestine that continues to the outside body opening, the cloaca.
d) Although associated with the digestive system, the spleen is actually part of the
circulatory system. It is found at the posterior end of the stomach. Describe the
spleen. What is its function?
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e) Locate the pancreas. It has two-lobes, the dorsal lobe coming from the right side of
the spleen on the dorsal side of the intestine, and the ventral lobe, which is ovalshaped, and sitting on top of the beginning of the intestine. What is the function of
the pancreas?
Sketch #2: Draw a sketch of the shark’s digestive system. Label stomach, liver, esophagus,
spleen, pancreas, intestine and cloaca.
4) Reproductive System
Female Urogenital System
Find the large paired ovaries at the ends of the kidneys. Eggs can usually be removed
from the ovaries. Open an egg and examine the yolk. At maturity, the eggs can be as
large as 3cm in diameter. The oviducts appear to be long thin tubes that are enlarged at
their anterior end to form a cuplike structure called the ostium. The ostium received the
eggs from the ovaries when they are mature. Posteriorly, the oviduct enlarges to become
the uterus. The uterus takes up 1/3 to 1/2 of the oviduct and is very large in pregnant
females. Embryos are often developing in the uterus. Cut it open and remove the
fetuses.
Male Urogenital System
Find the large paired testes in the same position as the ovaries. Sperm are produced by
the testes and passes into the efferent duct. This duct leads to the vas deferens, a coiled
tube that extends almost the entire length of the kidney. As the vas deferens approach the
excretory position of the kidney, they straighten and enlarge into the seminal vesicle.
Sperm sacs can be found near the cloaca. Unlike most fish, the shark exhibits internal
fertilization. During mating, one clasper on the male's pelvic fin is turned forward and
inserted into the cloacal opening of the female. The sperm move from the male's cloaca
into the groove on the dorsal surface of the clasper and then into the female.
5) Heart:
The heart is located in the head region of the shark, just above and to the inside of the
pectoral girdle. The heart is almost totally incased in the cartilaginous pectoral girdle and
the muscles that surround it. The heart lies in its cavity called the pericardial cavity. To
reach the pericardial cavity, continue the original ventral cut anteriorly through the
pectoral girdle and the surrounding muscles. Make a transverse cut just below the mouth
and fold back the flaps.
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Locate the heart. If you probe posterior to the heart, you should find a canal that
connects the pericardial and pleuroperitoneal cavities, showing that they are not
completely separate. Carefully examine the heart and locate the following structures:
atrium, ventricle, and sinus venosus. Also, locate dorsal aorta and ventral aorta.
Use the following link to answer the questions below:
http://www.flmnh.ufl.edu/fish/Gallery/Descript/Spinydogfish/SpinyDogfish.html
1. Looking at geographical distribution, could you possibly spot one of these on vacation in
Maine?
2. Could you find them in freshwater?
3. Where do you find the spines on a dogfish?
4. Give the average size and lifespan of a dogfish.
5. What makes up the majority of their diet?
6. What feeds on the dogfish?
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