Shark Dissection and Observation
BACKGROUND INFORMATION: Sharks are amazing creatures that unlike bony fishes have no bones. Instead their skeleton is made of a tough, fibrous material known as cartilage. In this lab activity, students will have the opportunity to handle a preserved shark and feel the cartilaginous skeleton. There are many species of sharks, and the size of sharks varies enormously. Some sharks are the size of a human’s hand, while others can be the size of a bus. However, most sharks are intermediate in size, and typically are similar in size to humans. Indeed, most sharks are between 1.5-2.1 meters long (5-7 feet). For practical purposes, the sharks used in this laboratory activity will be relatively small in size.
The body shapes of sharks vary. Most sharks are streamlined, and this streamlined shape allows them to easily move through the water. Other sharks, such as the angel shark, have flat bodies that allow them to easily hide on the bottom of the ocean floor. Some sharks have extra long snouts or very wide heads.
There are over 369 species of known sharks. The diets, appearance, and behavior of these sharks vary greatly. The shark used today is a dogfish sharks, (Squalus acanthias). It is the most abundant shark in the ocean. Its dorsal fin has spines that are mildly poisonous. Sometimes the spines are removed before classroom introduction. The dogfish shark is used extensively by people as food, fertilizer, hide, pet food, and liver oil. The name dogfish shark is due to the fact that they hunt in a pack. The spiny dogfish sharks have internal reproduction and ovoviviparous births. About 2-11 pups are in each litter, these pups are between 8-12 inches (20-30 cm) long. The gestation period is one of the longest of vertebrates, about 18-24 months after a winter mating. Male dogfish reach maturity at 11 years old; female dogfish reach maturity at 19-20 years old. The dogfish's life span ranges from 25-100 years. The diagram below details the anatomy of a dogfish shark.
Pre-Lab VOCABULARY and Questions: Define the Key Terms and Answer the Questions.
Chondrichthyes Claspers
Dorsal Fin Oviparous (Include Example Species)
Caudal Fin Ovoviviparous (Include Example Species)
Pectoral Fin Lateral-Line System
Ampullae of Lorenzini Placoid scales (with illustration)
1. Do sharks have bones?
2. What features of a shark’s anatomy or body allow it to be able to survive in the ocean?
3. What class are stingrays found in?
4. Are sharks aganthan fish or gnathostomes? Why?
MATERIALS:
Per lab group:
Preserved dogfish shark Dissecting Scope
1 set of dissection tools per lab group Color Pencils
Ruler Cleaning tools
PROCEDURE:
STEP 1: Touch the shark! All members of the lab group should touch the shark. Pick it up, squeeze it, feel it! Slowly and carefully run your hand along the shark's body, from head to tail and vice versa. Notice the difference in texture. The abrasiveness that you feel is the shark’s scales, called placoid scales. Using a scalpel to remove a piece of skin, examine it under a microscope. And record your observations
1. Describe the texture of the shark’s skin when you run your hand in both directions.
2. Describe and draw the microscopic illustration of the shark’s skin.
3. Does it feel like the shark has hard bones similar to the bones that humans have?
4. What part of the human body has a similar feel to that of the shark?
STEP 2: Draw your shark in the space provided on your worksheet. Draw a Side View.
Label the head, trunk and tail regions on your picture.
Color the shark the appropriate coloring; be careful for dorsal and ventral sides.
1. Why do you think it is colored this way?
Draw and label the Lateral Line.
2. What is the function of the Lateral Line?
Label the Anterior Dorsal Fin and the Posterior Dorsal Fin; if spines are present label those.
Label the Caudal Fin, Rostrum, and Spiracles.
Look in the mouth of your shark including the teeth.
3. Describe the teeth, including their orientation, number, ect.
STEP 3: Dissect the eye.
Make an incision along the side of the eye to cut the nictitating membrane. This membrane is a thin eyelid that the shark can see through. It protects the animal's eye from injury when it is attacking its prey.
1. Describe the nictitating membrane.
Remove the nictitating membrane to look at the eye. Shark eyes are very similar to the eyes of other vertebrates, including humans. They contain a lens, a cornea, and a retina.
2. How is the shark eye similar to a human eye?
STEP 4: Measure the shark! Use your ruler to measure the length of the shark, including the distance between the dorsal fins, and size of caudal fin. Remember to measure in cm!
1. How long is your shark?
2. What is the distance between the 2 dorsal fins?
3. What is the height of your caudal fin?
STEP 5: Observe the exterior of the shark. For the following structures, explain what they look like and list how they might help the shark survive better in its environment.
Ampullae of Lorenzini Spiracle
Lateral Line Caudal Fin
Gill openings Nostril
1. Determine whether your shark is a male or female.
STEP 6: Dissect! You can now dissect the shark.
The Internal Anatomy:
Using your scalpel and scissors make an incision down the center of the shark’s ventral side that starts in between the shark’s pectoral fins and extends down to its pelvic fins/girdle. Be careful to lift with forceps while you cut so as to not damage the internal organs. Make an “I” cut on either side of your incision that extends across the ventral side of the shark. This incision should be far enough out so that you can pin back the skin and easily view the organs.
A smooth, shiny membrane called peritoneum can be seen lining the inside of the body wall. The visceral organs are suspended dorsally by a double membrane of peritoneum know as mesentery.
Locate the shark’s liver. It is the largest organ lying within the body cavity. Its two main lobes, the right and left lobes, extend from the pectoral girdle posterior to most of the length of the cavity. A third, much shorter lobe is located medially and contains the green gall bladder along its right edge. The liver filters the blood and cellular waste material. It also keeps the shark buoyant. The liver is very oily, and this oil is lighter than water, helping the shark to float. (Q: Describe your shark’s liver.)
Move the liver to the side so that you can see the stomach. The esophagus is the thick muscular tube that extends from the top of the cavity connecting the oral cavity and pharynx with the stomach.
Cut open your shark’s stomach and describe any contents you find. The mucosa is the inner lining of the stomach. The rugae are longitudinal folds that help in the churning and mixing the food with digestive juices. A circular muscular valve, the pyloric sphincter, is located at the far end or pyloric end of the stomach. It regulates the passage of partially digested food into the intestines. (Q: What did you find inside your sharks stomach? Describe the contents. What can you conclude about your sharks eating habits from this dissection? Q: Explain what the rugae looks like and what its function is.)
Continue past the stomach into the intestines. You might need to move your liver to do this.
The duodenum is a short "U"-shaped portion of the small intestine that connects the stomach to the intestine. The bile duct from the gall bladder enters the duodenum. The pancreas is located on the duodenum and the lower stomach. The secretions of the pancreas enter the duodenum by way of the pancreatic duct. The dark, triangular-shaped spleen is located near the posterior end of the stomach. Although a part the Lymphatic system, the spleen is closely associated with the digestive organs in all vertebrates.
Pull the intestine forward so that you can view the colon, which is the narrowed continuation of the intestine. It is located at the posterior end of the body cavity. The rectal gland is a slender, blind-ended, finger-like structure that leads into the colon by means of a duct. It has been shown to excrete salt (NaCI) in concentrations higher than that of the shark's body fluids or seawater.
The cloaca is the last section of the canal. It collects the products of the colon as well as the urogenital ducts. It is where the wastes of the body are removed via the cloacal opening. (Q: What is the benefit of having a cloaca?)
Lift the liver, pancreas, and spleen in order to reveal the urogenital structures: gonads (testes or ovaries) and kidneys.The kidneys are located under the tissue running towards the caudal fin. (Q: Does your shark have testes or Ovaries? Describe their appearance and location.)
Cut across the gill slits from the pectoral fin to the corner of the mouth. You will have to cut across the ventral musculature to lay the area flat.The gills are provided with a rich blood supply. Arteries run directly from the nearby heart to the gills bringing deoxygenated blood into the gill lamellae. Lamellae are thin plates or disks that are in rows in the gills and greatly increase the surface area through which gas exchange can take place. Oxygen diffuses from the ventilating water current flowing over the gills into the blood.
From your “I” cut, make an anterior incision to reveal the heart. The heart has 2 main chambers; atria (which appears like a sack) and ventricle (harder structure, due to muscular pumping needs.) (Q: Describe the different chambers of the shark’s heart.)
Wrap up your shark and throw it away in the garbage bag provided by your teacher. Wash off all dissecting equipment and return items to area you got them from. Clean off dissecting area with disinfectant so classroom doesn't stink! WASH YOUR HANDS!!!!
Analysis & Conclusion Questions:
1. List 5 traits that the perch and shark shared (general fish traits).
2. List 5 traits/characteristics that were different between the perch and the shark (bony vs. cartilaginous fish traits).
3. What sensory organs did the shark have? List them all including what each did.
4. Discuss 3 adaptations for life in the water that the shark had.
5. What purpose do the spiracles serve? What do the gill lamellae do?
6. What type of scales does the shark have?
7. What is the purpose of the cloaca?
8. How does a shark maintain buoyancy (what does it use)?
9. Why do sharks move continuously?
Be ready for a Shark Anatomy Quiz. Know these items for sure!
Key Parts in Shark Anatomy:
· Spiral Intestines: Absorbs food for the shark to utilize as energy.
· Spleen: Associated with the digestive system, the spleen is actually part of the circulatory system.
· Stomach: J-shaped organ which digests (breaks down) food.
· Vas Deferens: Duct, which transports sperm from testes to claspers.
· Gall Bladder: used in urination process.
· Heart: pumps blood to other areas of body.
· Kidney: removes wastes from blood.
· Liver: Large organ which cleanse blood and stores bile.
· Pancreas: Produces digestive enzymes for transport to the spiral intestine.
· Pelvic Fin: Allows shark to change direction and aids in movement.
· First Dorsal Fin: Allows shark to change direction and aids in movement.
· Second Dorsal Fin: Allows shark to change direction and aids in movement.
· Snout: Front of sharks head, rostrum
· Spiracle(s): These are two openings behind the eyes. They allow water to pass through, allowing the shark to stop moving.
· Lateral Line System: Actually in the interior of the shark but visible from the outside, it helps sense low-frequency vibrations, aiding in pursuit of prey.
· Mouth: Food and water pass through to the body.
· Nostril: Allows shark to smell. Best sense organ.
· Pectoral Fin: Allows shark to change direction and aids in movement
· Caudal Fin: Allows shark to change direction and aids in movement.
· Claspers: Found only on male sharks, they enable the transfer of sperm during mating.
· Eye: Shark is able to see its surroundings.
· Gill Slits: Water passes through the slits effectively allowing the shark to breathe.
· Uterus: reproductive structure that holds offspring in ovoviviparous births