Fish Dissection Category: Biology: Anatomy & Physiology Type: Class Experiment (60 min class) Materials: 1 1 1 1 1 1 Fish (perch or mullet are best) Pair of disposable gloves Razor blade Pair of small scissors Pair of tweezers Plastic tray THIS EXPERIMENT INVOLVES THE USE
OF RAZOR BLADES. BE CAREFUL!
How To: Gather all materials. For classes we normally use perch, for this dissection it’s a mullet. Examine the fish – look at its skin, pull out the fins and look at their structure and shape. What are the fins used for? Hold the fish and guess how it would move in the water. © 2012 Mission Science Workshop. All Rights Reserved worldwide. When linking to or using ODC content, images, or videos, credit MUST be included. Locate the gills. These are protected by a covering known as the operculum. Separate the gills using tweezers. How many gills are there? Examine the fish’s mouth. Use fingers to pull open the mouth fully. How is it shaped? Based on it’s shape, how does this fish take in its food? Use tweezers to examine the direction in which water flows over the gills. Locate the small hole on the underside of the fish. What is this? © 2012 Mission Science Workshop. All Rights Reserved worldwide. When linking to or using ODC content, images, or videos, credit MUST be included. Cut the fish open from the anus up to the neck using a razor blade. Try not to cut too deeply. Stop when it becomes hard to cut. Examine the fish from this angle. Turn the fish on its side. Cut up towards the top of the fish from the two ends of the first incision, as pictured above. The flap of skin can be lifted to reveal the internal organs of the fish. Cut off the flap of skin. This makes it easier to examine the inside of the fish. Can you find the swim bladder? It normally consists of two sacs located in the dorsal portion of the fish. Locate the heart. It is normally situated behind the gills. © 2012 Mission Science Workshop. All Rights Reserved worldwide. When linking to or using ODC content, images, or videos, credit MUST be included. Remove the heart from the fish using the scissors and forceps. Cut open the heart, how many chambers are there? Identify and locate the liver. Remove the liver from the fish. Find the stomach of the fish. What is the stomach attached to? Cut the stomach open. Is there anything inside? Identify the spleen. It is a very deep, rich red color. © 2012 Mission Science Workshop. All Rights Reserved worldwide. When linking to or using ODC content, images, or videos, credit MUST be included. Looks at the intestines. Can you trace them from the stomach to the anus? What are the large yellow sacs? To find out, cut them open and examine the contents. Describe what is inside? If you find 2 of these sacks, the fish is a male. The next step is to dissect the eyes. Use the razor blade cut under the eye and lift it out. Can you see the difference between the muscles and nerves that are connected to they eye? What is the eye connected to? The skull can be opened to examine the brain. © 2012 Mission Science Workshop. All Rights Reserved worldwide. When linking to or using ODC content, images, or videos, credit MUST be included. Remove the eye from the fish using scissors to cut through the optic nerve. Using the razor blade and tweezers, cut open the eye. See what parts of the eye you can remove and identify. Can you find the lens? The dissection can be continued by removing the brain. Fine Points: → Any type of fish can be used. We use perch for full classes because they are affordable. → When cutting the underbelly of the fish, do not cut too deep; otherwise the gut tissues underneath may be destroyed. → The tissues can be examined under a dissecting microscope, if available. → Examine the fish scales and if available use a compound microscope → Remove the eye carefully; it is very easy to cut through the eye with the razor blade. → Adult help might be needed to remove the brain. → There are other parts of the fish that can be examined e.g. the bones, teeth. → If the dissection is performed in a clean environment using clean tools, the meat could be used to make dinner! Objectives: During this experiment students will: 1. Understand the definitions of anatomy and physiology. 2. Observe the external and internal anatomy of a fish. 3. Name, locate and identify the organs that make up various systems of the fish. 4. Identify similarities between fish and humans. Concepts Involved: •
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Various organs make up various systems of the fish. There are similarities and differences between the internal structures of humans and fish. Dissecting a fish allows the anatomy of fish and human bodies to be compared. The structure of a fish (and any animal) is related to how it has adapted to its surroundings. Focus Questions: 1.
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What is the fish body made of? What body parts do you find in fish that are also in humans? What parts of the fish have adapted for life in the water? What is the purpose of the different parts of the fish that were found? © 2012 Mission Science Workshop. All Rights Reserved worldwide. When linking to or using ODC content, images, or videos, credit MUST be included. Elaboration: This class is used to study anatomy. Anatomy is the study of the structure and function of the body. Anatomy does not focus only on the human body but also on animals and plants. A dissection is the best way to learn about the parts of the body and the insides, and to get a better understanding of how a whole body works together. Part 1. External Examination. The first part of this experiment is to examine the fish. Fish have adapted to live in water and one of their most distinctive characteristics are their fins. In bony fish, such as mullet and perch, the fins are composed of bony spines protruding from the body with skin covering them and joining them together. Fins help fish to move quickly through the water and to steer without rolling over. They are found in a number of different places on the fish, and each one has a different purpose, such as moving forward, turning, and keeping an upright position. The fins located on the back are called dorsal fins. They stop the fish from rolling over and allow it to make sudden stops. The pectoral fins are located on the sides and help to control movement and direction. In some fish the pectoral fins even aid in walking or flight! The fin closet to the anus is known as the anal fin. It helps to stabilize the fish when swimming. The pelvic fins, which are located below the pectoral fins, help the fish move up and down, turn and stop quickly. Finally there is the fish tail, also known as the caudal fin, this is used to drive the fish forward. “Non-­‐bony” fish (class Chondrichthyes), such as sharks have a skeleton primarily composed of cartilage, like that found in tip of our noses. Shark fins are stiff and lack the fine bony spines and muscle
control found in bony fish.
Fish are covered in scales. An interesting fact about scales is that the same genes that are involved in mammal tooth and hair development are also involved in scale development. Scales can also be used to tell how old a fish is! There are bands on the scales of fish that are similar to the rings of a tree, the number of dark rings determine how old the fish is. (A microscope is needed to do this.) Another distinctive feature of fish are the gills. Gills are used for breathing. They extract the dissolved oxygen in water and release carbon dioxide. They are made of thin filaments of tissue branches that are organized into folded structures that allow the surface area of gills to be large. This is important because there is less oxygen in water than in air and fish need to be able to take in enough oxygen so that they don’t suffocate. Fish breathe by taking in water through the mouth. Each gulp of water then flows into a gill chamber on each side of the head and over the gills. A hard bony covering, known as the operculum, protects the gills. Part 2. Internal Examination. The swim bladder (also known as air or gas bladder), is a gas-­‐filled organ that allows a fish to maintain its depth without floating upward or sinking, and to stay at a current water depth without having to waste energy in swimming. It is found only in ray-­‐finned fish, such as perch and mullet. Fish with no swim bladder such as mackerels, sharks, and rays must expend energy by constantly swimming in order to keep from sinking. A fish heart is one of the simplest vertebrate hearts. It consists of four parts, two chambers plus an entrance and exit. It pumps the blood in a single loop throughout the body and up through the gills. Fish ingest food through the mouth and break it down in the esophagus. In the stomach, food is further digested. The intestine completes the process of digestion and nutrient absorption. What’s left is excreted through the anus. © 2012 Mission Science Workshop. All Rights Reserved worldwide. When linking to or using ODC content, images, or videos, credit MUST be included. Fish reproductive organs include testes and ovaries. In perch, females have one gonad, while the male have two. Most fish lay their eggs, so the development of fish embryos occurs outside of the body, similar to birds. They lay thousands of them, so the egg sack takes up a significant space in the gut of the fish. Fish live in a different environment to humans and most other mammals. Their body structure has developed to be supported all over by the water they swim in. Marine mammals have also developed this way, but with different body and skeleton structures. Deep-­‐sea fishes have adapted to living in very dark waters at extremely high pressure. Fish eyes are similar to those of other vertebrates (e.g. birds, reptiles). Light enters the eye at the cornea, passing through the pupil and lens to reach the retina. The eye is connected to the brain via the optic nerve. Links to k-­‐12 CA Content Standards: Grades k-­‐8 Standard Set Investigation and Experimentation: Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other strands, students should develop their own questions and perform investigations. Grades k-­‐12 Mathematical Reasoning: 1.0 Students make decisions about how to approach problems: 1.1 Analyze problems by identifying relationships, distinguishing relevant from irrelevant information, sequencing and prioritizing information, and observing patterns. 1.2 Determine when and how to break a problem into simpler parts. 2.0 Students use strategies, skills, and concepts in finding solutions: 1.1 Use estimation to verify the reasonableness of calculated results. 1.2 2.2 Apply strategies and results from simpler problems to more complex problems. 1.3 Use a variety of methods, such as words, numbers, symbols, charts, graphs, tables, diagrams, and models, to explain mathematical reasoning. 2.5 Indicate the relative advantages of exact and approximate solutions to problems and give answers to a specified degree of accuracy. 3.0 Students move beyond a particular problem by generalizing to other situations: 3.1 Evaluate the reasonableness of the solution in the context of the original situation. 3.2 Note the method of deriving the solution and demonstrate a conceptual understanding of the derivation by solving similar problems. 3.3 Develop generalizations of the results obtained and apply them in other circumstances. Grade 3 Standard Set 3. Life Sciences. Adaptations in physical structure or behavior may improve an organism’s chance for survival. As a basis for understanding this concept: 3.a. Students know plants and animals have structures that serve different functions in growth, survival, and reproduction. Grade 5 Standard Set 2. Life Sciences. Plants and animals have structures for respiration, digestion, waste disposal, and transport of materials. As a basis for understanding this concept: © 2012 Mission Science Workshop. All Rights Reserved worldwide. When linking to or using ODC content, images, or videos, credit MUST be included. 2.a. Students know many multicellular organisms have specialized structures to support the transport of materials. 2.b. Students know how blood circulates through the heart chambers, lungs, and body and how carbon dioxide (CO2) and oxygen (O2) are exchanged in the lungs and tissues. 2.c. Students know the sequential steps of digestion and the roles of teeth and the mouth, esophagus, stomach, small intestine, large intestine, and colon in the function of the digestive system. 2.d. Students know the role of the kidney in removing cellular waste from blood and converting it into urine, which is stored in the bladder. Grade 7 Standard Set 1. Cell Biology. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As a basis for understanding this concept: 7.a. Students know cells function similarly in all living organisms. 7.b. Students know the characteristics that distinguish plant cells from animal cells, including chloroplasts and cell walls. Grade 7 Standard Set 5. Structure and Function in Living Systems. The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function. As a basis for understanding this concept: 7.a. Students know plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism. 7.b. Students know organ systems function because of the contributions of individual organs, tissues, and cells. The failure of any part can affect the entire system. 7.c. Students know how bones and muscles work together to provide a structural framework for movement. 7.d. Students know how the reproductive organs of the human female and male generate eggs and sperm and how sexual activity may lead to fertilization and pregnancy. © 2012 Mission Science Workshop. All Rights Reserved worldwide. When linking to or using ODC content, images, or videos, credit MUST be included.