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Concepts/Objectives | Vocabulary/Background | Activity | Extension
"WHAT'S ON THE INSIDE"
"Fish Dissection: Internal Anatomy"
Explain that you are going to dissect a fish. Have the students discuss the anatomic parts they would expect to find in a fish.
- List the parts they expect to find.
- Explain why they think each part will be present.
- Tell what they think may be the function of these different parts.
- List questions they would like answered when observing fish entrails.
INFORMATION FOR TEACHERS BEFORE BEGINNING:
- You will probably want to do the opening of the fish for the students, once this is done turn the fish over to the students. Insert a sharp knife in the anus and make a shallow cut along the belly to the area right below the gill opening. Open the body to identify as many organs as possible without removing them. Have them carefully tease the organs away from the body with their fingers.
WHERE TO FIND PARTS OF THE BODY
- Heart and Liver- The heart and liver are found right below the gills and cutting should be done carefully so they are not injured.
- Brain- The brain is on the front part of the head. You will need to cut through bone of the head to get at it.
- Eye- The eye can be removed and opened to reveal a round lens.
Sexing Fish- If fish are about to reproduce, the female ovary will be a sac, usually filled with yellow to orange eggs. The testis of the male will be a gray sac. When fish are not reproducing, the ovaries and testes will normally be difficult to find.
- Things to note:
- The mouth has two exits-one for water through the gills, one for food through the stomach.
- There are several gills on either side of the head.
- The black kidney is right against the backbone.
- The stomach can be opened to see what the fish has eaten.
- The air bladder will look like a cellophane sac.
DO NOT BE CONCERNED IF ALL BODY ORGANS ARE NOT FOUND (Remember that this is a first exploratory experience.)
- Clean a fish with the students while pointing out its internal anatomy. You may want to do this as a demonstration, or have the students follow along on their own fish.
The students should:
- Wear aprons
- Wash their hands
- Watch the opening of the fish (students will observe)
- Find each of the parts identified by the cleaner
- Seek answers to their own questions
- To open the fish, insert a sharp knife (or scissors) into the anus (see the following fish diagrams for reference) and make a shallow cut along the belly forward to the area just below the gill opening. You can make another cut from this point, perpendicular to the first, on the upper half of the fish from the belly to a point just behind the eye, and a third cut from the anus toward the dorsal fin. Make sure you are only cutting the muscular top layer of the fish, and not penetrating into the body cavity. The top layer (a fillet of the fish) can then be peeled back to reveal the internal organs.
- Have the students draw and label the internal parts of the fish. Have them use CLEANING FISH: INTERNAL ANATOMY to record their drawings.
T - I see this fish has a digestive tract similar to a human's. Food is taken in at the mouth and goes down to the stomach. The digestion starts here and ends at the intestine, where the food is absorbed. The wastes are passed out of the body. This is similar to the human digestive system. What did I find and how is it similar to the human organ?
S - You found the digestive tract and humans take their food in and get rid of their wastes the same way fish do. The organs are similar.
T - We seem to be very different, but some of our organs function the same way.
T - Does anyone see ovaries in their fish? Do humans have ovaries?
S - I see them, this must be a female fish because female humans have ovaries.
T - What is the function of the ovaries in the human?
S - They carry the eggs that can become babies.
T - Ovaries have the same function in the fish. (Draw and list function on chart)
T - With a partner, decide which organs are similar to human organs (find them in the fish). After ten minutes, I will call on volunteers to share what they have found. Tell me the organ, where it is found, and how the function is similar to the human organ.
S - We found a kidney and humans have kidneys. Kidneys are used to remove wastes from the body. It is near the intestine.
Additional Discussion Questions
- What parts of the fish's anatomy seem to be involved in processing food? Agree on the mouth, tongue, teeth, stomach, intestine, anus.
- How were these parts arranged in the fish?
- Where were the sex organs of the fish?
- How do eggs or milt (sperm) leave the body of the fish? Locate a second opening behind the anus. This is the urogenital opening.
- Where was the heart of the fish?
- How was the heart connected to the rest of the body? Only large blood vessels will be observable.
- Where were the kidneys of the fish?
- Where were the gills of the fish?
- How were they connected to the rest of the body? The blood vessels leading to the heart may be found.
- What questions of your own did you investigate? What answers did you find?