Perch Dissection

Introduction and Pre-Lab Information:

The fish in the class Osteichthyes have bony skeletons. There are three groups of the bony fish --- ray-finned fish, lobe-finned fish, and the lung fish. The perch is an example of a ray-finned fish. Its fins have spiny rays of cartilage &/or bone to support them. Fins help the perch to move quickly through the water  and steer without rolling.  Click HERE for more information about the fins found on the perch and their functions. The perch also has a streamline body shape that makes it well adapted for movement in the water. All ray-finned fish have a swim bladder that gives the fish buoyancy allowing them to sink or rise in the water. The swim bladder also regulates the concentration of gases in the blood of the fish. Perch have powerful jaws and strong teeth for catching and eating prey. Yellow perch are primarily bottom feeders with a slow deliberate bite. They eat almost anything, but prefer minnows, insect larvae, plankton, and worms.  Perch move about in schools, often numbering in the hundreds.

The scientific name for the yellow perch, most often used in dissection, is Perca flavescens (Perca means "dusky"; flavescens means "becoming gold colored"). The sides of the yellow perch are golden yellow to brassy green with six to eight dark vertical saddles and a white to yellow belly.  Along the side of the fish is the lateral line.  Click HERE to learn more about the lateral line and its functions.  Yellow perch have many small teeth, but no large canines. Yellow perch spawn from mid-April to early May by depositing their eggs over vegetation or the water bottom, with no care given. The eggs are laid in large gelatinous adhesive masses.

At this time, you are to answer the Pre-Lab Questions on your Perch Dissection Review Worksheet.

 

Image result for fish jumping gif

Materials:

Preserved perch, dissecting tray, scalpel, scissors, forceps, Brock microscope, dissecting pins, length of string , ruler or meter stick

Procedure (External Anatomy):  Perch Dissection Video Part 1

  1. Obtain a perch & rinse off the excess preservative. Place the perch in your dissecting pan.

  2. Use your string and ruler or meter stick to determine the total length, fork length, and girth of your fish. Record  this in Table 1.

 

  1. Locate the 3 body regions of the perch --- head, trunk, and tail. Label these on Figure 1.

  2. Open the perch's mouth and observe its bony jaws.  The upper jaw is fixed and will not move.  The mandible is the moveable part of its jaw.   Locate and label the upper jaw or maxilla and the lower jaw or mandible.

  3. Feel the inside of the mouth for the teeth. Locate the tongue & teeth on Figure 1.

  4. Open the mouth wider and use a probe to reach back to the gill chamber.

  5. Find the lateral line on the side of your perch. Label this line on Figure 1.

  6. Locate the nostrils and label on Figure 1.

  7.  Locate and note the location of the eyes. Label on Figure 1.

  8. Find the bony covering on each side of the fish's head called the operculum. The opercula cover & protect the gills. Label this on Figure 1.

  1. Use a probe to lift the operculum and observe the gills. Note their color.

  2. Use a scissors to cut away one operculum to view the gills.  There should be two pairs of gills on each side of the perch (4 total gills).   Find the gill slits or spaces between the gills.  Click HERE to find more information about gill rakers.

  3. Use your scalpel to carefully cut out one gill. Find the cartilage support called the gill arch and the soft gill filaments that make up each gill. Label the parts of the gill in Figure 2 on your lab review.

Fish Gill Anatomy

The gill structure on the right is the one that will be found in your perch.

 

    

There are four sets of gills on each side of the perch as seen in the above diagram.

  1. Observe the different fins on the perch. Locate the pectoral, dorsal, pelvic, anal, and caudal fins. Note whether the fin has spines. Complete Table 2. with the information about the fins.

  1. Locate the anus on the perch anterior to the anal fin. In the female, the anus is in front of the genital pore, and the urinary pore is located behind the genital pore. The male has only one pore (urogenital pore) behind the anus. Determine the sex of your perch.  Record this on your lab review worksheet.
  2. Use forceps to remove a few scales from your fish. Observe the scales under the Brock microscope. Sketch what you see on your lab review worksheet.

Close-up View of a Perch Scale

The age of the fish the scale above was taken from is 7 years.

  1. Count the growth rings on your scale to tell the age of your fish. (Hint: each ring represents one year's growth.)  Click HERE for more information about fish scale growth rings.
  2. Click HERE for more information about fish scales in general.

 

Procedure (Internal Anatomy): Perch Dissection Video Part 2

  1. Use dissecting pins to secure the fish to the dissecting pan. Use scissors to make the cuts through skin and muscle shown below.

 Cut Lines for Internal dissection

  1. After making the cuts, carefully lift off the flap of skin and muscle to expose the internal organs in the body cavity.
  2. Locate the cream colored liver in the front of the body cavity. Also locate the gall bladder between the lobes of the liver. Label these on Figure 3 on your lab review worksheet.
  3. Remove the gall bladder & liver to observe the short esophagus attached to the stomach. Label the stomach on Figure 3 on your lab review worksheet.
  4. At the posterior end of the stomach are the coiled intestines. Locate and then label these on Figure 3 on your lab review worksheet.
  5. Find the small reddish brown spleen near the stomach and label this on Figure 3 on your lab review worksheet.
  6. Below the operculum, are the bony gill rakers. Locate these & them label them on Figure 3.
  7. In front of the liver & behind the gill rakers is the pericardial cavity containing the heart. The heart of a fish only has 2 chambers --- an atrium & and a ventricle. Locate the heart & label it on Figure 3.
  8. In the upper part of the body below the lateral line is the swim bladder. This sac has a thin wall and gives the fish buoyancy. Label the swim bladder on Figure 3.
  9. Below the swim bladder are the gonads, testes or ovaries. In a female, these may be filled with eggs. Label the gonads on Figure 3.
  10. Find the 2 long, dark kidneys in the posterior end of the perch. These filter wastes from the blood. Label the kidneys in Figure 3.
  11. Wastes exit the body through the vent located on the ventral side of the perch. Label this structure on Figure 3. 

 

Complete the Post-Lab Questions on your Perch Dissection Review Worksheet

Click HERE for the Perch Dissection Lab Companion