FISH LAB
Name........................................pd.........
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 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?____________________________.
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?________________________________________
C.
Examine the gills covering of IIC....is there an operculum??___________
Describe what you see ____________________
______________________________________________________________________________________
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
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?__________
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?_____________
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.
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? _____________
NERVOUS SYSTEM
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.