The Perch
Vertebrate & Freshwater Animal
Osteichthyes, bony fish, are dominant in the seas. You may have eaten many of
these animals – herring, cod, flounder, tuna, salmon, and others. The bony fish are the
only fishes that have successfully invaded the fresh waters of the world and established
themselves in great populations in rivers, ponds, and streams. The mighty shark and their
close relatives, the rays and skates, have been unable to colonize the freshwater world.
Dorsally on the snout are two, double, external nostrils which are openings to the
olfactory sacs. These sacs are highly sensitive to dissolved chemicals in the water. It is
similar to our sense of smell.
There is no external ear, but each internal ear contains semicircular canals, which
are balancing organs that enable the fish to maintain the proper position in the water.
The lateral line extends along each side of the whole body of the perch. The
lateral line system is essentially a series of water-filled canals, which communicate, via
pores, with the water in which the fish swims. This system is believed to register
vibratory currents both by moving objects in the water and the swimming movements of
the fish itself. The system therefore functions as a sensitive “listening” device to detect
water turbulence and to discriminate between different kinds of turbulence.
Thin rounded scales in lengthwise and diagonal rows cover the trunk and tail.
Each scale has structures called growth rings. As a fish grows, the size, rather than the
number of scales, increases. As the scale grows, concentric rings are formed. Rings
formed in the fall and winter are closer together than those formed during the spring and
simmer. By counting the number of regions of closely spaced concentric rings you may
determine the number of winters the specimen lived – the age.
Perch Dissection
Objectives:
• To observe the external and internal anatomy of a perch.
• To determine the sex of a perch using internal anatomy.
• To collect statistical data on the perch
Procedure:
External Examination 1. Measure the head, trunk, and tail in centimeters. The head region extends
from the tip of the snout to the hind edge of the operculum. The trunk region
is from the hind edge of the operculum to the anus. The tail region is from the
anus to the longest tip of the tail. Record your measurements in Table 1.
2. Place the perch so that the head is facing towards your left side.
3. Draw the external lateral view of the perch and label as Figure 1. Make sure
to shade any areas that are darker on the perch.
4. Label the following external structures: Nostril, Eye, Maxilla, Mandible,
Operculum, Pectoral Fin, Pelvic Fin, Anus, Urogential Opening, Anal
Fin, Caudal Fin, Lateral Line, Dorsal Fins.
5. Count the number of spines that are located in the first dorsal fin. Record
your answer in Table 1.
6. Remove a scale from the perch. Use your fingers or the forceps to pull scale
from the body. Mount the scale as a wet mount slide and observe it under
LOW power of a microscope.
7. Note the annual growth rings. Make a sketch of the scale for Figure 2. Label
the following: Growth Rings. Read the introduction if you do not remember
how to count the rings!
8. Record the average age of your perch in Table 1.
9. Cut away the operculum from the left side and examine the gills. The space in
between the gills is called gill silts or gill clefts.
Internal Examination –
1. Hold the perch ventral side up and the head pointing away from you. Insert
the point of your scissors through the body wall in front of the anus and cut up
the midline of the body to the space between the opercula.
2. Now lay the fish on its right side (with the head on your left) in the dissection
pan. BE CAREFUL NOT TO DISTRUB THE INTERNAL ORGANS!
3. Continue to cut up around the back edge of the gill chamber to the top of the
body cavity.
4. Make another incision from the starting point of the ventral incision close to
the anus and cut upward to the top of the body cavity.
5. With a scalpel, remove the whole lateral body wall by cutting along the top of
the body cavity. You should now see the internal organs!
6. Make a sketch of the perch with the internal organs for Figure 3. Label the
following BEFORE you cut the organ out of the body. (LABEL): Liver,
Gallbladder, Esophagus, Intestine, Spleen, Ovary/Testes, Air Bladder,
Kidneys, (Urinary) Bladder, Heart,
Digestive System:
7. Locate the reddish-brown liver in the anterior end of the body cavity
(LABEL). Raise the lobes of the liver and find the gallbladder attached to
the lower side (LABEL).
8. Cut the liver free from its attachment to the body and remove it. This will
expose the esophagus and the stomach (LABEL).
9. Follow the stomach posterior to find the intestine (LABEL). Follow the
loops of the intestine to find the anal opening. You may see long masses of
fat lying along the intestinal loops.
10. Observe the spleen attached to an internal mesentery near the stomach
(LABEL). Mesentery is the thin membrane that holds the intestine loops tight
together. It is a dark, red-colored gland that has no duct and no functional
connection with the digestive system.
11. Carefully cut the esophagus and remove the alimentary canal, from the
esophagus to the anus. BE CAREFUL! You may need to cut membrane of
move organ out of the way.
Reproductive System:
12. With the alimentary canal removed, the gonads should be visible and maybe
the urinary bladder.
Female – Ovaries will lie between the intestine and the swim bladder. It
is a sac filled with eggs (LABEL). The posterior end of the ovary tapers
down into a tube that leads to the urogential opening.
Male – Testes are a pair of white, elongated bodies lying just below the air
bladder. There is a thin mesentery that is attached to the testes. They fuse
together toward the posterior end to make a tube that leads to the
urogential opening.
13. Record the sex of your perch in Table 1.
Swim Bladder/Air Bladder:
14. Locate the air bladder along the top of the body cavity (LABEL). The
bladder is filled with gases (O,N,CO2)
Excretory System:
15. Remove the air bladder from the body. A pair of long, barrow, dark-colored
kidneys should be seen (LABEL).
16. The urinary ducts run along the kidneys and join the urinary bladder
(LABEL).
Circulatory System:
17. With a point of your scissors make a horizontal cut through the anterior wall
of the body cavity in front of the liver. This will expose the peritoneal cavity
in which the two-chambered heart lies. The heart consists of a light colored
ventricle and a larger atrium (LABEL).
Skeletal/Muscular System:
18. Locate the vertebrate column. Remove a section of the vertebrate to observe
the structure. Observing under the dissection microscope will show more
detail.
19. Removing the skin layer from the tail section of the fish will allow the view of
the muscles.
Data:
Figure 1: External Lateral View
Figure 2: Scale – Growth Rings
Figure 3: Internal View
Table 1: Perch Dissection Information
Measurement of the Head Region
Measurement of the Trunk Region
Measurement of the Tail Region
Number of Spines on the First Dorsal Fin
Approximate Age of Perch
Sex of Perch
cm
cm
cm
Analysis:
Hint: Most of the answers to the following questions can be found in the introduction.
1. What are the olfactory sacs and what do they do for the perch?
2. Do perch have ears? If they do what are they used for?
3. What if the purpose of the lateral line?
4. How are the growth rings on the scales formed and thus counted to find age?
5. What is the purpose of the soft mucus-producing epidermis for a perch?
Conclusion:
Restate all hypotheses and explain if each is correct or incorrect.
Successfully prove knowledge of objectives was gained.
These are the objectives of the lab. Make sure to prove you gained knowledge about them.
-To observe the external and internal anatomy of a crayfish.
Hint- pick 4-5 interesting things discovered from dissecting and inform the
reader about them.
-To determine the sex of a crayfish using external anatomy.
Hint: explain to the reader how to determine a male and a female crayfish.