Download Perch Dissection 1. Do the nostrils lead into the

Perch Dissection
Today you will be dissecting a yellow perch (Perca flavescens). Perch are part of the largest group of vertebrates with a bony skeleton,
known as osteichthyes. Perch are also ray-finned fish belonging to the family actinopterygii because their fins are supported by “rays”
of bony spines.
A. External Anatomy
Place a preserved perch in a dissection tray and examine the head region. On each side of the mouth is a semicircular flap called the
operculum, which covers and protects the gills. Water enters the mouth, flows over the gills and leaves through the opening covered by
the operculum.
Locate the fish’s nostrils. Inside the nostrils are olfactory organs, which detect chemical substances dissolved in water. Insert a probe
into one of the fish’s nostrils. Open the mouth to see if the probe comes into the mouth.
1. Do the nostrils lead into the mouth?
2. Do the nostrils play any role in the fish’s breathing?
a. How do you know?
Open and close the perch’s mouth to observe the action of the mandible (lower jaw) and maxilla (upper jaw). Examine the teeth. Note
the appearance of the teeth and which direction the teeth point.
3. Are both jaws of the fish equally movable?
a. Explain your answer.
4. What is the advantage for the teeth facing the way they do?
Examine the fish’s six types of fins. On its dorsal side is the spiny anterior dorsal fin and the soft posterior dorsal fin. Its tail is a
homocercal caudal fin. On its ventral side is the anal fin, located near the anus and the pelvic fin. Just behind the fish’s head is the
pectoral fin.
5. How many fins does a perch have?
6. How does this number of fins compare to how many fins a dogfish has?
Find the fish’s lateral line, a series of grooves along its side that run nearly the length of the fish. Ciliated cells in the lateral line called
neuromasts are sensitive to vibrations in the water. These cells allow the fish to tell if another animal is moving through the water.
7. Why is important that neuromasts are ciliated?
8. On the outline of the drawing below label the following: operculum, lateral line, nostril, anterior dorsal fin, posterior
dorsal fin, pelvic fin, caudal fin, anal fin, pectoral fin
B. Internal Anatomy
Respiratory system: Using scissors, cut the operculum off of one side of the fish to expose the gills. Each gill consists of feathery gill
filaments attached to a gill arch. Gill arches give support to the gill filaments and the gill filaments are where oxygen and carbon dioxide
exchange occurs. These filaments are also filled with capillaries that carry blood from the heart. Locate the gill rakers on each gill arch.
These projections separate the gill arches from each other and create spaces between each arch. Remove a portion of one gill by
cutting it at its point of attachment. Examine the feathery structure.
9. How does the feathery structure of the gills aid in gas exchange?
10. Label the following structures on gill diagram below: gill rakers, gill arch, gill filaments
To expose the fish’s internal organs, you will cut out a section of the muscular body wall. Make an incision with scissors close to the
anus. Cut forward to the gills (where you removed the operculum). From the top of the gill area, cut along the body to a point above
your first incision. Cut downward to the incision. Carefully remove the flap of body wall. Cut carefully to avoid destroying the organs
beneath the body wall.
Digestive system: Find the large, tan-colored liver with the bile storing gall bladder attached to and underneath the liver. The liver
makes the digestive enzyme known as bile. Cut the liver free from the body to expose the short esophagus attached to the stomach.
Food enters the digestive tract through the mouth, passes through the throat like pharynx into the esophagus and enters the stomach.
The stomach capacity is increased by several pouch like structures called pyloric caeca. Find the small, reddish-brown spleen located
between the stomach and intestine. After being partially digested in the stomach, food enters and digestion is completed in the winding
intestine. Undigested food is removed through the anus.
Reproductive system: Determine if your fish is a male or female by locating either a pair of testes, small, pale yellow masses on the
ventral side or a single, large, yellow ovary filled with eggs. The testes and ovaries are connected by tubes to the urogenital opening
found posterior to the anus. Fertilization in a perch is external and gametes of both males and females are released through this
opening.
11. Is your fish male or female?
Circulatory system: Cut through the fish’s body wall anterior to where the liver was located. Doing this will expose the pericardial cavity
where the heart is suspended. Find the one thin-walled atrium and the one thicker-walled muscular ventricle. You may be able to
locate the one enlarged vein (sinus venosus) where blood enters the heart and the one enlarge artery (bulbus arteriosus) where the
blood leaves the heart. The blood leaving the heart goes to the gills where it flows through capillaries and then through the body in
various veins and capillaries and arteries and finally returns to the heart to be pumped through the body again.
12. How does the number of heart chambers in a fish compare to you as a mammal?
13. Which heart chamber does most of the pumping?
a. How do you know?
The swim (air) bladder lies between the gonad and the kidneys. Bony fish use a swim bladder to regulate their position in the water.
The fish inflates the air bladder with gases produced in the blood. As the amount of gas in the bladder changes, the fish’s vertical
position in the water changes.
14. What structures do you have as a land animal similar to the functioning of a fish’s swim bladder?
15. How is having a swim bladder an adaptive advantage for a bony fish?
Excretory system: Lying just beneath the spine are the kidneys, which appear as dark masses of tissue. Kidneys absorb liquid waste
products from the blood. The liquid waste is excreted as urine through the urogenital opening, located just behind the anus.
16. On the outline of the drawing below label the following: esophagus, swim bladder, gills, gonad, kidney, stomach,
heart, liver, anus, intestine, pyloric caeca, urogenital opening.
17. What organ in the perch is most closely related in function to a human’s ear?
18. Explain how the swim bladder controls buoyancy.
19. Write the function and system for each of the following structures:
Operculum –
System –
Neuromasts –
System –
Gill filaments –
System –
Pyloric Caeca –
System –
Urogenital opening –
Systems (2) –
Bulbus arteriosus –
System –
Kidney –
System –