Materials Included In Kit

Additional Materials Required

Prelab Preparation

Note: Students can prepare the meter sticks and protractors if time is available.

1. Depending on materials available, set up as many water stations for testing speed as possible. Fill the containers—aquariums or clear plastic totes—about half full of water.
2. On a meter stick, mark a starting point 8 cm from the left edge of the container with a sticky note.
3. On the same meter stick, mark a finishing point 8 cm before the right edge of the container with a sticky note.
4. Place the meter stick across the top of the container (see Figure 4 in the Procedure).
5. With permanent marker, draw a starting line and finishing line on the face of the aquarium to aid in start/stop accuracy. The starting line should line up with the starting mark on the meter stick, 8 cm from the side. The finish line should line up with the finish line on the meter stick, 8 cm from the side (see Figure 4 in the Procedure).
6. Prepare the protractors for the students by marking (with permanent marker or sticky note) 5° on either side of 90° to show the maximum deflection allowed.
7. Divide the clay into 15.0-g samples. Each individual should receive their own piece of clay to create the fish design. Students work in pairs to assist each other with timing, record keeping and brainstorming. However, each student will have their own independent data. 

Safety Precautions

Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. Enough clay is provided for each student to make an individual fish body design. Both parts of this laboratory activity can reasonably be completed in two 50-minute class periods. The prelaboratory assignment may be completed before coming to lab, and the data compilation and calculations may be completed the day after the lab.
• You will need to set the length of the fishing line as a constant variable based on the container used. Ideally the fish should hang in the middle of the water. Students may attach the fishing line in any manner. Through sample trials, a successful method was to bore a hole using a paper clip through the model fish and thread the line through the center of the model.
• Prior to testing, instruct students to manipulate the model so that it hangs from the fishing line horizontal to the ground.
• The length of the fishing line depends on the container used. Keep the length of fishing line consistent for all trials.
• If the container is large enough, two tests may occur simultaneously. For example, the width of a 29-gallon aquarium is 31 cm. Two meter sticks can be placed on top allowing two groups to test at the same time.
• Depending on the container used, speeds may not vary greatly. Longer containers will result in greater variance in speeds between body forms.

Teacher Tips

• This activity can be utilized during an evolution chapter to demonstrate fitness and natural selection while incorporating the practice of model design.
• Ideally, a streamlined, sleek body shape with a small cross-section (which reduces drag) is the fittest fish body shape.
• A snake-like body shape will appear to be a better forward swimmer. This is due to the artificial force (student) moving the fish. A fish with this body shape, like the moray eel, would need to undulate the body for motion, slowing the speed.
• Possible extensions for this activity can include varying the materials the students are allowed to use to construct their fish models, varying the water type in which the students are testing the model (fresh, brackish, salt) or determining how mass affects the speed—allowing the use of more or less clay.

Answers to Prelab Questions

1. Explain how natural selection leads to changes within a species.

   Individuals with inherited traits well-suited to the environment leave more offspring on average than other individuals. Over time there will be more individuals with traits well-suited for the environment and fewer individuals with traits less suited, which could lead to physical changes within the species.

2. Calculate the average speed of a cheetah that chased an impala 260 meters in 9 seconds before it made the kill.

   Speed = distance/time
   260 m/9 s = 28.9 m/s

3. Predict the body shape that would allow for the fastest fish, which, in this investigation, indicates the highest level of fitness. Explain your prediction.

   Student answers will vary but should lead toward a streamlined body to reduce drag. Also, students should mention the role of fins in providing stability and preventing rolling.

Sample Data

Part C. Tesing Fish Models**

*Data obtained from a 29-gallon aquarium. Dimensions are 76 cm x 31 cm x 47.5 cm
**Data for disk-like, flat body with 1 dorsal fin, 1 anal fin and vertical pectoral fins.

Part D. Improved Fish Design^†

†Data for streamlined body with 2 dorsal fins, 1 anal fin and vertical pectoral fins.

Answers to Questions

1. Describe the reasoning behind your original design. What features were included to make it have the fastest speed?

   Accept all reasonable responses. Look for answers that include a streamlined body design to reduce drag as it is being pulled through the water. Students should discuss fins chosen, two dorsal fins to prevent rolling, anal fin used for extra stability, etc.

2. Compare your data with other groups. Based on the data, would evidence support or refute the claim that “Your original fish design displayed high fitness”? Explain the reasoning for your answer.

   Student answers will vary but must include data, speed from trials, to support or refute the fitness of their fish design. A streamlined body design should demonstrate the fastest times indicating higher fitness for this challenge.

3. Describe an environment where nature would select for your fish body shape.

   Accept all reasonable responses. Answers may include open oceans with few obstacles allowing for maximum speed to be achieved in pursuit of prey or to escape predators.

4. Describe an environment where nature would select against your fish body shape.

   Accept all reasonable responses. Answers may include coral reefs, heavy vegetated ponds or lakes, and other aquatic environments with several obstacles that would require a flexible, disk-like body shape providing maneuverability.

5. Describe changes made to the original design in order to improve the speed of the fish. Using evidence, explain whether you were successful or unsuccessful.

   Accept all reasonable responses. Answers must include data, speed from trials, to prove whether their improved design increase speed.

6. Describe any limitations present in your data (discuss possible sources of error).

   Accept all reasonable responses. Answers include precision of measurement, for example, the starting mechanism is imprecise. Having to eye-ball estimate when the fish head crossed the finish line which may influence speed calculations. The line itself increases drag and may not be consistent in each trial. Allowing for 5º deflection of the line adds some variability to the data.

7. List the similarities and differences, focusing on the structures and functions, between a real fish and your model.

   Accept all reasonable responses. Similarities may include functions of the fins providing stability and preventing rolling. Differences may include the movement not coming from undulation of the body or the caudal fin, but rather the student. Another difference would be that in the aquarium the water is still, and in rivers or the ocean there may be currents affecting movement. Fish skin or scales are designed for ease of movement through water and the clay may affect the movement. Finally, fish have flexible bodies to assist in movement through the water, the model does not.

8. Look at the following fish and body shapes. What would be their evolutionary advantage as a predator?
   1. Mako Shark: Streamlined body shape—fastest body design for straight movement, speed to catch prey.
   2. Moray Eel: Snake-like body shape—lurks in narrow crevices, lies in wait for prey, bursts of speed.
   3. Bass: Flexible body, trap mouth—quick forward movement, pounce on prey, large mouth.
9. Look at the following fish and body shapes. What would be their evolutionary advantage as a prey species?
   1. Flounder: Flat body shape—lays on seafloor, blends in with seafloor.
   2. Butterfly fish: Disk-like body shape—maneuver in all directions, avoid predators, warning colors or false appearances.

Introduction

What makes a living thing fit? Fitness can be increased by traits that benefit survival and reproduction. An example of an animal many would consider fit is the great white shark (Carcharodon carcharis). Their dark dorsal surfaces (backs) allow them to blend in against the dark, rocky bottom of the ocean floor and their white ventral surfaces (bellies) help them blend in with the sunlight when viewed from below. Tooth-like scales cover their bodies to reduce drag and noise generated by movement. The jaw is not fused, which allows their triangular, serrated teeth to extend out when attacking prey. Advanced eyes give the shark color vision and night vision while exceptionally large gills aid in ample oxygen exchange, making the great white shark a fit predator.

Concepts

• Adaptations
• Natural selection
• Adaptive radiation
• Survival of the fittest

Background

What is fitness, and what allows an organism to have high fitness? Fitness is the contribution an individual makes to the gene pool—all the alleles available in a population—compared to the contributions of others. In other words, an individual with high fitness is capable of surviving to reproductive maturity and producing many healthy, fertile offspring that in turn can survive to reproductive maturity. Most falsely assume that fittest means the largest, strongest or fiercest individual; however this is only the case when those traits help in survival and reproduction. A wild rose with an alluring, sweet fragrance attracts more pollinators than a wild rose with a less aromatic scent, thus the former has a higher level of fitness.

How does an individual attain a high level of fitness? Fitness is achieved through adaptations. Adaptations are inherited characteristics that improve fitness. Through natural selection these adaptations improve an organism’s ability to survive and reproduce in a particular environment. Charles Darwin (1809–1882) first presented his idea of natural selection in 1859 when he published On the Origins of Species. Using data he collected from the Galapagos Islands, a set of volcanic islands off of South America, he explained this concept as descent with modification. The finches Darwin observed on the islands were similar to a finch from the mainland in many ways, but ultimately belonged to different species.

He noticed that the island finches differed from each other as well. He explained that an ancestral finch population migrated to the islands from the mainland—descent—and changed over millions of years after colonizing the islands due to differences in the environment—modification. The accumulated changes to the finch species came in response to diverse island ecosystems, leading to different diets. Some finches developed stout, thick beaks excellent for cracking seeds. Other finches developed longer, thinner beaks that allowed them to pick insects out of trees or off the ground. This process of one ancestral species giving rise to multiple species that exploit different niches—the full range of resources required for survival and reproduction—is called adaptive radiation. Diversity among finches was ultimately determined by the environment and food availability.

Natural selection acted upon individual finches. Those with inherited characteristics well-suited to the environment had more offspring on average than other individuals. For example, the finches with thick, stout beaks survived at higher rates in environments with seeds as a food source. They produced offspring and passed those characteristics to their offspring. The offspring, in turn did the same, leading to survival of the fittest finch—the finch with the thickest, stoutest, seed-cracking beak. If this finch had migrated to an environment where insects were the primary food source, it would have had low fitness because its beak was not adapted to the new food source.

Just as the finches adapted—and continue to adapt—to food and diverse island life on the Galapagos Islands, fish also adapt to the environmental pressures of aquatic life. The body shape of a fish is related to the niche it fills. For example, fish with a streamlined body shape, like the tuna, have adapted to life in the open ocean. They swim long distances in search of food and mates while avoiding predators. They move seamlessly through the water in opposition to friction and drag due to their narrow, forked tails and sleek body shape. Fish that rest on the ocean floor, like the sting ray, typically have flat bodies with eyes on top of their heads allowing them to hunt prey above them. They move by making wave-like motions with their bodies, and are usually camouflaged to blend in with the sandy ocean floor. There are as many fish as there are niches and therefore many adaptations to exploit those niches.

Experiment Overview

The purpose of this investigation is to design and mold a clay model of the fish body shape you believe is capable of the fastest speed across an aquarium. Speed is calculated by dividing distance by time. The fish model must have all the given design criteria and deflect no more than 5 degrees from its vertical support as it moves across the aquarium.

Materials

Prelab Questions

1. Explain how natural selection leads to changes within a species.
2. Calculate the average speed of a cheetah that chased an impala a total of 260 meters in 9 seconds before it made the kill.
3. Predict the body shape that would allow for the fastest fish, which, in this investigation, indicates the highest level of fitness. Explain your prediction.

Safety Precautions

Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Part A. Fish Model

1. With one piece of clay, shape and mold a fish body that will move efficiently through the water.
   {11294_Procedure_Figure_2}
2. Fish requirements:
   1. All 15 grams of clay must be used in the design.
   2. Fish must have a minimum of one dorsal fin (see Table 1 and Figure 2).
   3. Fish must have two pectoral fins.
   4. Anal fins and pelvic fins are optional.
   5. Caudal fin must be vertical, not horizontal.
      {11294_Procedure_Table_1}
3. Draw the fish design on Fish Fitness Worksheet.

Part B. Fish Attachment

1. Affix a small paper clip through the hole on the straight edge of the protractor as shown in Figure 3. This creates an easy attachment and removal system for the fishing line in order to make adjustments to the design. Tie a knot in the fishing line to create a loop and attach to the paper clip.
   {11294_Procedure_Figure_3}
2. Thread the fishing line through the body of the model fish. Adjust the fishing line so that the fish hangs down 90° from the top of the protractor. Adjust the fishing line on the fish so that the fish hangs parallel (horizontal) to the ground as well.
3. Adjust the length of the fishing line to the predetermined length set by the instructor.

Part C. Testing Fish Models

1. Position the fish in the water so the “head” is at the start mark on the meter stick (see Figure 4).
   {11294_Procedure_Figure_4}
2. Hold the protractor so the straight edge is at the top. Note: The fishing line should be taut and hang straight down, crossing the 90° mark on the protractor.
3. Practice moving the fish through the water at a constant rate so the deflection remains steady.
4. Use the meter stick as a guide to keep the protractor level as the fish is pulled through the water. The fishing line will not hang straight down due to the resistance of the water, causing the fish to lag behind. The faster the fish is pulled, the more the fishing line will deflect. To keep competition fair, adjust the movement to keep the fishing line deflected by 5° or less as marked on the protractor. As the fish is pulled through the water, the deflection mark cannot be passed by the fishing line. If it is, discard that run.
5. After a practice run, return the fish to the start mark of the meter stick.
6. One partner sets the stopwatch.
7. Determine a “go” signal and move the fish from the start mark to the finish mark.
8. Time from the “go” signal until the head of the fish, not the fishing line, reaches the finish mark.
9. Repeat steps 6–8 for three trials.
10. Record the time on the worksheet.

Part D. Improved Fish Design

1. After completing the trials with the original fish, calculating the speed and recording observations, make improvements to the original fish design to increase speed/fitness.
2. Follow the same requirements for clay usage, required fins and fishing line length.
3. Practice moving the improved fish design through the water at a constant rate of deflection.
4. Record data on Fish Fitness Worksheet for three trials with the improved fish design.

Student Worksheet PDF

11294_Student.pdf