FISH LAB
Name
FISH LAB Name........................................
Fish possess bony skeletons and their gills are covered with a thin bony cover, the operculum. Their bodies are
covered by large overlapping scales arranged like shingles on a roof. The fish are highly successful; and are found in
almost all bodies of water and show great diversification in form and habitat.
PURPOSE:
The purpose of this lab is to observe the body plan of the bony fish and be able to compare it to other members of its
phylum and other marine organisms studied.
MATERIALS:
Fish Dissecting kit Dissecting pan scale dish
Dissecting and regular microscope slides.
PROCEDURE:
USE THE DRAWINGS TO HELP LOCATE THE ORGANS
A. EXTERNAL ANATOMY
The main body regions of the fish are the head, trunk and tail (caudal fin). The head extends from the tip of the
snout to the hind edge of the operculum, the trunk from this point to the anus, and the remainder is the tail. Examine the
head and observe the large mouth which has distinct upper and lower jaws. The upper jaw is the 'maxilla' and the lower is
the 'mandible'. Examine the two external 'nares' on the snout which are openings to the 'olfactory sacs' which are
sensitive to dissolved chemicals in the water. The 'eyes' are without lids and behind each eye is the bony 'operculum'
which provides protective covering for the four comb-like respiratory gills.
1. Weigh your specimen and record the weight here._____________
2. Cut away one operculum and examine the gills, cut away one gill arch, place it in water and examine it under the
dissecting microscope. The spaces between the gills are called gill slits. Attached to the lower edge of the operculum is
the branchiostegal membrane supported by rays of cartilage and it serves as a one way valve which allows water to pass
out the opercular opening but not in. Draw the gill (magnified) and label it in the space to the right.
B. The lateral line is a series of water-filled canals which communicate with the water in which the fish swims and is
Page 1
FISH LAB
Name
believed to register vibratory currents from both moving objects in the ocean and those made by the fish itself.
3. Where is the lateral line located on your fish and how long is it compared to the entire body length of the fish?
_________________________
________________________________________________________________________
4. Listed are the types of fins. Supply the number, location and function of each.
FIN NUMBER LOCATION FUNCTION PELVIC
PECTORAL
DORSAL
ANAL
CAUDAL (TAIL)
C. INTERNAL ANATOMY
Hold the fish with the 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 mid-line of the body to the space between the opercula. Now
lay the specimen on its right side (head to your left) in the pan, and continue to cut up around the back edge of the gill
chamber to the top of the body cavity. Make another cut from the anus to the top of the cavity and with a scalpel,
remove the whole body wall by cutting along the top of the body cavity, taking care NOT to disturb the internal organs.
This will expose the body organs in their normal positions.
5. Locate the reddish-brown liver in the anterior end of the body cavity. Examine the size in relation to the body.
Is it large or small?____________ What is the weight of the liver?______ What proportion of the body weight
is the liver ( liver weight divided by fish weight = % body weight of liver)____________
6. Under the lobes of the liver is the greenish gall bladder. After removing the liver, the esophagus and stomach
are exposed. Locate the pylorus where the stomach and the intestine join.
7. Examine the loops of the intestine and find where it leads to the anal opening. What are the masses of yellow
substances lining the intestine?______________.
8. Remove the alimentary canal and you should see the gonads clearly. Locate the ovary which lies between the
intestine and swim bladder if your fish is a female or the testes, if your fish is a male, which lie below the swim bladder
and are attached to the mesentery and lead toward the posterior end where sperm is passed outside through the
__________________opening. During early stages, the ovaries are paired but during development, they fuse into a
single organ.
9. Along the top of the body cavity is the Air or Swim Bladder. This is filled with gases and can adjust the specific
gravity of the fish to the water at different depths. How are gases taken in or given off from the bladder?
_______________________________________________________
10. Remove the air bladder and notice the large blood vessel near the middle. This is the 'dorsal aorta'. Parallel to
it is a pair of long narrow, dark colored kidneys, the 'urinary ducts (ureters)' run along the edges of the kidney and join to
empty into the urinary bladder (near the gonads). What does the kidney remove?____________________________.
Page 2
FISH LAB
Name
11. Cut through the anterior wall in front of the liver to expose the 'peritoneal cavity' in which the two chambered
heart lies. The heart consists of a single, light colored ventricle and a larger thin-walled atrium. Locate the vessels
carrying blood to and from the heart. Find the ventral aorta which carries blood from the ventricle.
Where does this vessel lead?____________________________
12. Hold the fish with the head pointing away from you and cut the skin of the skull and scrape the carefully to
wear away the bone. Pick out the pieces when the bone gets thin and locate the 'olfactory lobs' in the front, the larger
lobes of the 'cerebrum' behind these, and the very thin 'optic lobes' posterior to the cerebrum. The 'cerebellum' is
posterior to the optic lobes, and the 'medulla' is the enlargement where the 'spinal cord' joins the brain. Is this your first
brain surgery?__
D. AGING FISH
Determining the age of fish is an important aspect of fisheries biology. The need to know the age and weight of the
fish is important to determine the greatest yield per unit effort. Information is gathered on the sex, weight, length and
age of the fish from random sampling and from catches by commercial fisherman. Parts of a fish commonly used in aging
are the scales and the bones.
13. Once you have determined the sex of your fish, take some scales from the outer body (stay away from the
lateral line) and make a slide with a few scales. Observe under low power or high power under the dissecting scope.
Growth in fish is not continuous over the entire year. During the winter the circuli get closer together indicating slower
growth. When they get so close they don't reach all the way around the scale, its called an annulus or year mark.
14. Record the age of your fish, using the central point to the first annulus equals 0 year growth. The first to
second annulus is the first year growth and so on. AGE OF FISH__________ SEX OF FISH_________
15. Compare data to the rest of the class. Is there a correlation between age and length or age and weight?
________ Compare the male vs. female growth rates._______________________________________
16. Examine a few scales. Why is it important to age more than one scale?___________________________
17. Examine the other types of scales provided. What type of scale does your fish have?________
II
Examine the other fish on display.
A. How does the fish labeled IIA swim?_____________________________________________
B. What part of the fish labeled IIB assists in that fishes locomotion?
Page 3
FISH LAB
Name
________________________________________
C. Examine the gills covering of IIC....is there an operculum??___________ Describe what you see
____________________
______________________________________________________________________________________
Page 4
FISH LAB
Name
SHARK DISSECTION
Species: Squalus acanthias (spiny dogfish)
Distribution and Range: Spiny dogfish are found off both the Atlantic and Pacific coasts of the U.S.
NOTE!!!
Listen to directions before you cut anything. The first thing you should do is examine the shark externally. Is your shark a male or
female?
Be careful when cutting! Delicate structures can be destroyed very easily with sissors and probes.
Know what you are doing before you cut anything!!
When you find a structure you don't recognize, look first at the chart and/or diagram. Think about it. Then ask your lab partner their
opinions. If you still cannot answer your own question, ask the teacher.
Compare your shark with other teams. If your shark is a male, examine a female specimen etc.
Examine some structures under the microscope and fill out the worksheets pertaining to the parts.
Take notes and make sketches during the dissection if you wish.
Observation sheet
Page 5
FISH LAB
Name
External anatomy
Fusiform shape countershading epidermis dermis external nares external gill slits
pectoral fin dorsal fin pelvic fin caudal fin cloaca rostrum
ampulae of lorenzini lateral line
Digestive system
Liver esophagus gall bladder stomach duodenom pancreas
spleen rectal gland kidneys mesentary spiral intestine
Reproductive glands
Female: uterus oviduct ovary
Male: testes clasper sperm duct seminal vesicle vas deferens
Record the following data:
Common Name:_______________________ Scientific Name:_______________________
Length (overall):____________________
1. Number of gill slits:___________ 2. Are gill opercula present?_________
3. Where is the cloacal opening located?____________________________________
4. Are the gonads (testes in male, ovaries in female) present?___________
5. What sex is your shark?__________
Page 6
FISH LAB
Name
6. Describe the surface color of your specimen?____________________________
7. Describe the texture of the skin surface?_________________________________
_____________________________________________________________________________
8. Gently pass your hand over the surface of the sharks skin in an anterior to posterior direction. Then pass your hand gently from
posterior to anterior. Which direction provides the least resistance?_________________
9. Locate the lateral line, a series of sensory receptors, on each side of the shark. The lateral line senses vibrations under the water.
What is the overall length of the lateral line in your specimen?___________________
10. Press on the pores of the Ampullae of Lorenzini. What do you notice?
__________________________________________________________________________
11. Locate the paired nostrils. Gently insert a blunt probe into one of the nostrils. Water circulates through the small sac that you can
feel within the nostril. How might water circulation help the shark in locating food?
_____________________________________________________________________________
12. Examine the eyes. How do they differ from mammalian eyes like ours?
____________________________________________________________________________
13. Open the mouth of the animal. Do you see any teeth?_____________________
14. With the mouth of the animal held open, feel for the presence of teeth with a fingertip. Record
findings._______________________________________
15. Are teeth present on both upper and lower jaws?_____________
Page 7
FISH LAB
Name
Internal Observations
Expose the viscera by making a median longitudinal incision, ventrally, beginning at the clocal opening and proceeding anteriorly.
DIGESTION
1. Describe the liver. Size:_________Number of lobes:_________
Texture:______________ Color:________________
Locate the stomach and open it with a longitudinal incision.
2. Does the stomach contain food?_________
If so, what is present?_________________________________________
3. Describe the internal apperance of the stomach:______________________
________________________________________________________________________
The intestine begins at the posterior end of the stomach where there is a muscular valve (sphincter) and extends to the anus inside the
cloaca. The intestine forms an S-shape and then suddenly enlarges. The spleen and the pancreas are attached at the bends of
the S. Inside the enlarged portion there is a spiral membrane which greatly increases the absorptive surface without increasing
the length of the intestine. This membrane is called the spiral valve and is not found in the bony fishes.
4. How long is the intestine?_________________
The spleen is an important site for blood formation and is usually gray.
5. What color is the pancreas?_________________
The pancreas produces important digestive enzymes.
Page 8
FISH LAB
Name
The kidneys are dark elongated structures, running the length of the body cavity on either side of the mid-dorsal line. In mature
animals the oviduct in females and sperm ducts in the males may be seen running from the gonad to the cloaca in the same region
as the kidneys.
6. Is your specimen mature enough to notice the ducts?_________
RESPIRATION
Water is taken into the mouth and pharynx, passes over the gill filaments, through the gill slits, and on to the outside. During this
process, oxygen is removed and transported into the circulatory system and CO2 is released from the blood at the gill lamellae
and exits via the gill slits.
Insert a blunt blade of a pair of sissors into the right corner of the shark's mouth and begin cutting posteriorly through the angle of
the jaws across the gill slits as far back as the pectoral girdle. You should be able to lie the specimen flat in your tray.
1. Examine the teeth. Describe how they are arranged in the mouth.
_________________________________________________________________________
2. Is the sharks tongue as movable as that of higher vertebrates (you)?____
3. Locate then spiracles. How many?_____ Where do they lead? _____________
Page 9
FISH LAB
Name
NERVOUS SYSTEM
Page 10
FISH LAB
Name
THE BRAIN
The advantage of studying the sharks brain is that (1). the skull consists of cartilage and can easily be cut with a scaple blade, and (2).
it is relatively large so smaller nerves and structures can be observed and (3). it illustrates the lower level of development of
vertebrates but with the basic plan laid out. (to follow steps see page 91 of the shark handout)
Use the following diagrams to assist you during the dissection.
Page 11
FISH LAB
Name
Page 12