ETOL Lessons

The Activity:

I. Introduction - What is a Fish? (45 minutes)

  1. Pass out the Student Research Notes pages either as a packet or as individual parts as you move through the activity, and discuss the goal of the activity.

  2. To get students thinking about what defines a fish, ask them the question; "What is a Fish?" then have them draw and label their answer on page 1 of the Student Research Notes. Encourage students to include features, behaviors and other traits they think all fishes have, and therefore that could be used to identify an organism as a fish.

  3. Students should compare and discuss their fish drawings and labels to see how their ideas compare. Explain to students that defining "fish" is not very easy, even for ichthyologists.

  4. Pass out Fish Resource Guide. This reading contains several sections that include information about the characteristics of fishes, classification, reproduction, and phylogeny that can be used as a reference throughout the activity. Students should read the first section only, What is a Fish? to learn how ichthyologists define "fish," then summarize the characteristics that define "fish" in the Fish Checklist on page 1 of the Student Research Notes. Students should also note exceptions to the general fish characteristics at the bottom of the page.

  5. Discuss the following questions as a class. Students can take notes in the Student Research Notes on page 2:

    1. What characteristics did your team overlook? Answers will vary.

    2. After reading What is a Fish?, what surprised you most about defining a fish? Answers will vary.

    3. Of the features you listed and discussed, which ones do you think are useful for understanding the evolutionary history of fishes and how different fishes are related?
      Discuss with students that not all features are useful for determining relatedness. Scientists look for synapomorphies, derived or "changed" character states shared by two lineages within a clade, to help them understand relatedness. Students might want to review the Evolutionary Classification of Fishes section in Fish Resource Guide to see examples of shared characters, contrast typical ideas about fishes with a definition based on synapomorphies, and emphasize the problems with focusing only on overall similarity. Get more information.

    4. What role does evolution play in defining something as a fish? Students should be note that "fish" does not represent a monophyletic group or clade (e.g., does not include the most recent common ancestor and all descendants), and typical definitions of fish are not based on phylogeny or shared evolutionary history.

    5. What types of scientific questions do you think ichthyologists investigate? A wide range of answers is possible. Studying the evolution of fishes and how different types of fishes are related should be part of the discussion.


Deep Sea
Mystery home
Activity 1 Activity 2 Activity 3 Activity 4 Activity 5 Activity 6