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Question Set: What is a fish?


  1. Imagine that someone who has never seen a fish before asks you to teach them about fish. What would you tell them? Answer the question by writing down your own definition of what a fish is. 
  2. Compare your definition with a group of your peers and work together to develop a definition what a fish is. Record your groups’ definition of a fish and then answer the following questions:
    1. Did your peers have some ideas that you had not thought of?
    2. Did you agree with everything in their definitions? If you did not, what did you not agree about? 
    3. Did you change your mind about anything you put into your original definition? 
  3. Consider the examples of different animals in Table 3.1. For each example, answer the following question in the table:
    1. Based on your groups’ definition, is this animal a fish? 
    2. Do you want to change your fish definition based on this example, and if so, how? 
  4. Use Table 3.1 to help you modify your written definition so that it is your best description of a fish. 
    1. Look back over the organisms in the list. If you think they are fish, then make sure they fit your definition. 
    2. If you think they are not fish, make sure the wording of your definition excludes them. For example, shrimp fit the definition of “an aquatic animal that breathes with gills”. Since a shrimp is not a fish, you would need to modify this definition to exclude shrimp. 
  5. Why do you think it is so challenging to define what a fish is? 
  6. Why do you think that some animals are called fish when they are not really a fish, for example, jellyfish?
  7. Why do you think that fishes make up over half of the species of vertebrates? 
  8. Why do you think more new species of fishes are being discovered than the other animals?
  9. Practice using the term fish and the term fishes. For each of the following cases, indicate which term is correct (fish or fishes):
    1. A single skipjack tuna is a __________.
    2. A school of skipjack tuna is a school of __________.
    3. A school of eels, groupers and wrasses is a school of __________.
Table 3.1. Determine if the following animals are fish.
Animal Attributes Is it a fish? Do you want to change your definition of a fish based on this example, and if so, how? 
Minnow This animal does not live in the ocean; it only lives in streams and lakes. It has a bony skeleton, including a backbone, fins, scales, and gills. It is cold-blooded, and lays eggs.     
Shrimp This animal can be found in oceans and freshwater. It has no backbone or internal skeleton. It breathes with gills and is cold-blooded.    
Shark This animal is primarily found in the ocean. It has a skeleton made of cartilage, not bone, many gill openings, and tough skin with tooth-like elements embedded in the skin. Most (although not all) are cold-blooded and most give birth to live young (but some lay eggs).    
Lungfish This cold-blooded animal lives in freshwater and breathes with a lung as well as with its gills. It has fins and sometimes scales, and it can spend long periods of time out of water.    
Eel This cold-blooded animal has a single gill opening and a bony skeleton. Some eels have no scales and no side fins, but they do have a top fin and a tail fin, sharp teeth and a muscular body.    
Mud-skipper This animal has a bony skeleton and fins but no scales. It can breathe under water with its gills or in the air through its skin. Mudskippers can crawl on the land for long distances, and they can spend a lot of time out of the water. They are cold-blooded and lay eggs.    
Tadpole This cold-blooded animal has a backbone, lives in the water, has a long tail, and breathes with gills.    
Lamprey This animal has a cartilage skeleton, no jaws and many gill openings. It does not have scales or side fins. It is cold-blooded and lays eggs.     
Hagfish This oceanic animal has a very rudimentary cartilage skeleton, no jaws, no eyes, many gill openings, and no scales or fins. It is cold-blooded and lays eggs.    
Whale This oceanic animal has a bony skeleton, including a backbone. It has fins, but no scales (although it does have some hair). It is warm-blooded and gives birth to live young.    


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Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.