On the Cutting Edge: Extend Water Quality Studies Using the Yellow Perch
If your class is participating in World Water Monitoring Day activities, you have probably already explained the core set of water quality parameters, including temperature, pH (acidity), turbidity (clarity), and dissolved oxygen (DO), to your students. You can extend your students’ understanding of how these parameters affect aquatic life by studying the yellow perch, a common freshwater member of the bony fish, or osteichthyes, group.
The yellow perch requires high-quality water to stay disease free and grow in a healthy population. Oxygen must remain high and CO2 low. pH must be within a range of 6.0 to 9.0. Temperatures must meet specific requirements for perch to spawn. Yellow perch can be indicators of a body of water’s ecological condition, because they prey on organisms whose populations may decrease in poor-quality water. You can have your students research other information about water quality and perch growth to further their understanding of the importance of high-quality water.
Conducting a perch dissection lab gives students a hands-on understanding of the fish’s anatomy and how water quality affects its physiology. Here’s an excerpt from the Perch Dissection BioKit® to get you started:
- Obtain a dissecting tray and a set of dissecting instruments.
- Lay the perch on its side in the dissecting tray.
- Use Figure 1 to identify the parts of the external anatomy.
- Carefully lift the posterior edge of a scale without breaking it. Grasp the scale with forceps and pull posteriorly to remove it.
- Examine the scale with a hand lens or stereomicroscope. This is a ctenoid scale, so called because of the ctenii (teeth) on its posterior edge. The anterior edge appears frilled and has grooves, or radii, which radiate from a center, or focus. Ctenoid scales are characteristic of fish with bony spines in their fins.
- Beginning at the junction of the head with the body, remove the skin from one side of the perch to the posterior edge of the anal fin.
- Notice that the muscles occur in W-shaped blocks. Each block is called a myomere. Contractions of the myomeres bend the fish’s body, producing the swimming motions.
- Lift the operculum on the left side (the perch’s left) and make the cuts indicated by the dotted line on Figure 2. This will expose the gills.
- Lift one gill and cut it free. Place the gill in a small cup of water and examine it under a hand lens or stereomicroscope, identifying the parts shown in Figure 2.
- The branchial arch is a bone that supports the soft gill filaments. The anterior edge of the gill arch has comb-like projections called gill rakers. These help to screen out debris that might clog or damage the gills. Gas exchange occurs through the thin walls of the gill filament.
- Remove the outer gills. Count the gills on each side of the perch.
- Beginning at the point indicated by the arrow in Figure 3, make the incisions indicated by the dotted lines. As you cut, be careful not to damage the internal organs. When possible, leave the internal membranes intact and in place. Lift away the body wall.
- Identify the structures shown on Figure 4.
- If you have a female fish, the ovary may be enlarged with eggs. If so, it may be necessary to remove the ovary to clearly see the other abdominal organs. It may also be necessary to do some extra trimming to see the kidney head, the urinary bladder, and the swim bladder. The kidney runs dorsal from the kidney head to the swim bladder as a thin bit of dark tissue. Fat will often be found in the membranes attached to the intestines.
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