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Identifying Fish With Dichotomous Keys

By Jason Howe

Ever wonder how scientists identify fish by their scientific name? It has to with many physical traits such as the number and shape of their fins, the shape of their body, and many other things.

Using dichotomous keys, and creating individual dichotomous keys, are learning standards in most middle school science curricula. It teaches students how living things are grouped together by scientists, ultimately leading to their Genus and species name, making up their scientific name.

Fish Lesson Objectives:

The following New York State Intermediate Science learning standards are addressed in this lesson:

S2.1d use appropriate tools and conventional techniques to solve problems about the natural world, including: classifying

Standard 4 General Skills:

5. classify objects according to an established scheme and a student-generated scheme

6. develop and use a dichotomous key

Materials Required: Fish Classification Handout.

Lesson Procedure:

1. Students will learn about how living things are classified, or broken up into groups based on similar characteristics.

2. Students will use their classroom textbooks or some on line tools to practice using dichotomous keys. It usually helps to start with some simple ones, such as classifying shapes (triangle, square, rectangle, etc. based on number of sides). Some examples of websites featuring dichotomous keys are listed below. I have used all of these in my classroom and they are fun for the students to do:

3. Download the attached document is a dichotomous key activity involving drawings of fish.


Any of the activities listed above could be used as assessments after several practice runs. Make sure that a complete assessment involves the students creating their own dichotomous key as well as using one that is already done for them.

If students do well with the lab, perhaps no further labs would be required. If the teacher detects problem areas, more labs could be created to practice these skills. There are lots of things that can be named or classified to create dichotomous keys for. Students typically enjoy using and creating dichotomous key activities.