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Fins & Scales: An Introduction to Bony Fish—A Marine Science Project Guide for 4-H Leaders and Educators1

Karen Blyler 2

The full version of this Project Guide for 4-H Leaders and Educatiors is available to view in PDF format here. (For youth, the Project Guide for 4-H Intermediate Members is available here.)

The following text has been excerpted from the PDF version of the Leaders and Educators document.

About the Fins and Scales Project

The Fins and Scales Project is intended for Intermediate 4-Hers (11–13 years), yet open to any youth interested in learning about fish. The project provides youth with opportunities to investigate fish and their adaptations for living in water. As a result, youth practice a variety of science skills and life skills. Youth conduct their own research, make observations and comparisons, use critical thinking skills, communicate to others what they have learned, and can even teach others about fish!

If you have youth that like marine science and would like to do other projects in this topic, visit the 4-H website at Youth are encouraged to share what they learn through the Marine Ecology project through demonstrations, illustrated talks, photography entries, just to name a few. To discover opportunities for sharing project learning consult with your local UF/IFAS Extension 4-H agent.

Figure 1. The 4-H Fins and Scales Project provides youth with opportunities to investigate fish and their adaptations for living in water.
Figure 1.  The 4-H Fins and Scales Project provides youth with opportunities to investigate fish and their adaptations for living in water.
Credit: Photos in this publication taken by Karen Blyler and many 4-H members

About the Leader's Guide

The Youth Project Book is divided into sections based on the physical characteristics of fish. The Leaders Guide follows the layout of the Youth Project Book and provides a suggested approach for each section. Each section of the Leaders Guide contains:

  • Additional background information on fish adaptations.

  • Answers to questions found in the youth guide. Although answers are provided, it is important that you let youth discover their own answers for the greatest learning benefit.

  • Additional ideas and/or descriptions of activities to support learning in youth.

  • The identification of life skills and/or science process skills being practiced in the activities.

  • "Let's Review" section provides opportunities for youth to apply what they learned to a new situation.

  • "Dive Deeper" section provides ideas that allow youth to further explore a concept, question, term, or process.

  • "Think Like a Scientist!" section asks youth to investigate a question further to find possible answers and solutions.

Introducing the Fins and Scales Project

Suggested Approach

Have youth complete the first page by filling in their name and contact information. Then ask:

  • Why did they choose to do the Fins and Scales project?

  • What do they already know about fish?

  • What do they want to learn about fish?

  • What are the project goals? Discuss as a group how each goal below might be accomplished.

  • What materials do youth need to complete the project and how will they obtained?

  • What will be the timeline for completing the project?


Goal 1 - Youth should complete the following sections in their project guide.

A. What is a fish?

B. How do fins help a fish?

C. How does body shape help a fish?

D. How does body color help a fish?

E. Why do fish have different mouths?

F. Why do fish have scales?

G. How can we determine a fish's age?

The Leaders Guide contains answers to many of the questions found in the sections of the Project Book. The Helper's Guide also contains additional questions that may be helpful in guiding learning.

Goal 2 - Youth should participate in a learning experience related to fish. A "learning experience" can be one of the suggested activities found in the sections in this guide, or another activity related to fish. Your club could go on a fishing trip, tour a fish research facility, or participate in an aquarium program. They may also enter the State Marine Ecology Event. This annual contest recognizes youth for their achievement in marine science. For more information, go to the Florida 4-H website.

Goal 3 - Youth should mentor or help another youth through a learning activity. Within the sections are suggested activities. Once youth do these activities within the club, they could teach one activity to younger youth at camps, clubs, schools, festivals, etc.

Goal 4 - Youth should share what they have learned in the project with others. This could include speaking to a group about something they learned, an illustrated talk or poster display at a local, district, or state event.

What Is a Fish?

Purpose: This section introduces fish and some of their adaptations.

Suggested Approach: At a club meeting, introduce fish by finding out what youth already know about them. Sample question are below. (Most answers are in the "Background Information.")

  • How would you describe a fish?

  • What features do fish have that help them live in water?

  • What are the two main types (or classes) of fish?

  • How are these two classes alike yet different?

  • What is an ichthyologist?

Youth can complete the section tables and questions as a group or at home. Later discuss their answers. Additional activities are suggested in "Lets Dive Deeper" and "Think Like a Scientist!"

Background Information: A fish, as most people think, is an animal that has fins and lives in the water. Fish can breathe, smell, hear, and move around but not as we do. There are many different kinds of fish and all have special adaptations that help them survive in water.

Most fish fall into one of two taxonomic classes. Bony fish are in the class of fish called osteichthyes (os-te-ich-thyes) and have a skeleton made of hard bone. Other fish, such as sharks, skates, and rays, have skeletons made of cartilage and are in the class chondrichthyes (kan-drik-the-ez). Cartilage is soft flexible connective tissue. We have cartilage in our nose and ears.

Both groups have jaws, gills, paired fins, scales (most!), and are considered cold-blooded. This project will focus only on the bony fish. There are about 23,000 different kinds of bony fish and they can live in fresh or saltwater, sometimes both! Some examples of bony fish include: bass, snapper, tarpon, catfish, herring, flounder, and swordfish.

Did you know? The field of science that studies fish is called ichthyology. A scientist that studies fish is called an ichthyologist.

How Do Fins Help a Fish?

Purpose: This section helps youth learn the names and functions of the different fins fish have.

Suggested approach: As the project helper, you can help youth begin this section by asking the questions below. Youth can then complete this section at home. At the next club meeting be prepared to ask them about their progress and what they learned. It would be helpful to have a fish model or real fish to help them review the different fins. Find out what youth already know about the fins of the fish.

  • Why are fins important for a fish to have?

  • Can youth describe what the purpose is of each of the fins on the fish below?

  • Can they describe the function of each one?

  • What do we call the study of a fish's body structures?

Background: Bony fishes have different kinds of fins for different purposes. Each fin plays an important role in the survival of the animal. The body structures of an animal, such as the fins of a fish, are part of the animal's anatomy. The anatomy of a fish can give us lots of "clues" about how it lives!

For more information on different types of fins, refer to the PDF version of this document here.

How Does Body Shape Help a Fish?

Purpose: Youth will investigate the role body shape has in helping a fish survive in the ocean.

Suggested approach: Youth can complete this section as a group or at home. However, to introduce it, find out what youth know about the shapes of fish. Here are some possible questions.

  • Why do fish have different shapes?

  • How would they describe the different shapes?

  • Can they give examples?

To further introduce the role body shape has in a fish's survival, do the activities found in the PDF version of this document here.

How Does Body Color Help a Fish?

Purpose: To help youth describe how color and patterns play a role in a fish's survival.

Suggested Approach: Youth may complete this section as a group or individually at home. To introduce the importance of colors and patterns in a fish's survival, do the activities found in the PDF version of this document here.

Why Do Fish Have Different Mouths?

Purpose: This section provides opportunities for youth to investigate the different types of mouths fish have and how they are used for getting food.

Background: The type of mouth a fish has can give you a clue as to what and where it eats in the water. A fish with a very large mouth surrounds its food and often swallows it whole. A fish with a small mouth may eat small bits of food or prey. Fish with a sucker-shaped mouth (or mouth on underside) feed near the bottom and search the sediment for food. Fish with long duckbill-like jaws (pickerel or gar) will use their jaws to grasp the prey before swallowing it. Fish with jaws that angle upward (like snook and tarpon) feed more on prey near the surface.

To read the Suggested Approach section and its related activites, view the PDF version of this document here.

Why Do Fish Have Scales?

Purpose: This section introduces the different types of scales bony fish can have and why they are important. Youth will need to use their own fish or at least scales from some other fish.

Background: Most fish have scales. Scales are used for protection, much like our fingernails. Rather than protecting just a little part of a fish's body, scales help protect a fish's skin from being cut by sharp objects. Scales also have color pigments which give the fish its coloration. Fish scales are covered with a protective layer of slime. This slime helps to protect the fish from diseases and parasites.

Some fish such as catfish have no scales and are said to be "naked." Other fish such as trout and freshwater eels have scales that are very small. The scales are so small on these fish that many people think that they are naked like the catfish. Some fish have very large scales. A tarpon fish, which can grow up to five feet or so, has scales that can be three inches around!

To read the Suggested Approach section and its related activites, view the PDF version of this document here.

How Can We Determine a Fish's Age?

Background: When a fish hatches, it has small scales covering its body. The center (focus) of an older fish's scale represents that scale when the fish was newly hatched. As the fish grows the scales get larger. Rather than growing smooth like our fingernails, scales produce small circular growth rings around themselves. These growth rings are called circuli. A fish grows faster in the summer and slower in the winter. Circuli formed during the summer are widely spaced. Circuli formed in the winter, however, are spaced very close together. A dark ring is formed where the circuli are spaced close together. The darker ring of circuli is called the annulus. The age of a fish can be determined by counting the number of annuli on its scales.

To find out about this section's activites, view the PDF version of this document here.

Helpful Vocabulary

Anal fin – The fin that is located under the fish and between the anal vent and the tail.

Barbels – These are located under the mouth or the chin of the fish. They are slender whisker-like strands that have a sensory function.

Caudal fin – The tail of the fish. The tail can be shaped differently, depending on where the fish lives and how it moves in the water.

Camouflage – A coloration that helps a fish blend in to match its surroundings. This helps it to hide from predators.

Countershading – When a fish is dark on its upper side and light on its lower side. This helps a fish "hide" in open water. The dark color helps the fish blend in with the bottom when viewed from above. The light color helps the fish to blend in with the sky when viewed from below.

Disruptive coloration – When a fish has bars, stripes, spots or patches of color to break up an animal's outline in the water.

Dorsal fin – The fin on the back (or top) of the fish. This fish may be one long fin or divided into different fins. The fin may have spines and/or rays to support it.

Forked tail – This type of tail has longer top and bottom extensions than the center. Looks like a sideways "V". This tail helps a fish accelerate but provides less maneuverability.

Fusiform – A body shape that is tapered at each end and helps in streamlining the fish. A tuna is an example of a fish with a fusiform body shape.

Heterocercal tail – The upper and lower parts of the tail are NOT symmetrical (not the same). This type of tail helps propel the fish forward and provides some upward lift.

Homocercal tail – The upper and lower parts of the fin are symmetrical (the same). This helps the fish swim at moderate speeds over long distances.

Lateral line – The sensory organ that detects vibrations in the water. It looks like a line that runs along each side of the fish.

Lunate tail – This type of tail is curved or shaped like a crescent. Looks somewhat like a flat "C"! Not as good for maneuvering but great for speed over long distances.

Otoliths – These are bony structures found in a fish's inner ear. They are located in the head. Otoliths can be used to determine the age and growth rate of fish.

Pectoral fins – The paired fins found on each side of the fish just behind the gill opening.

Pelvic fins – The paired fins located on the underside of the fish, just under or further back from the pectoral fins.

Rays – Soft supporting fin structures.

Rounded tail – This tail has a rounded edge. It allows for good acceleration and maneuvering but creates drag and will allow a fish to tire more easily.

Spines – Stiff supporting fin structures. Spines may make it difficult for predators to eat the fish. The spines on some fish may contain painful toxins.

Truncated tail – This tail has a flattened edge and is good for maneuverability and making shorts bursts of speed.


1. This document is 4H355, one of a series of the 4-H Youth Development Department, UF/IFAS Extension. Original publication date June 1994. Revised October 2014. Reviewed October 2017. Visit the EDIS website at
2. Karen Blyler, 4-H state science coordinator; UF/IFAS Extension, Gainesville, FL 32611. Original version written by Ben Crenshaw, 4-H marine education specialist; UF/IFAS Extension, Gainesville, FL 32611.

Publication #4H355

Date: 11/5/2017

  • Critical Issue: Youth


  • Sarah Hensley