Zoology 511
Spring 2006
Lab 1 - Fish Anatomy
Goals



Identify structures important in the identification of species
Acquire basic understanding of the anatomical structure of fishes
Introduce concept of functional morphology
Readings
Helfman et al. 1996. pg. 37-50.
External Anatomy (lamprey, dogfish, white perch)
Most of our fish identification will be based on external anatomy. Therefore it is essential to be able to
identify key characteristics of fish external anatomy.
In the field, the coloration of fish can be important to their identification. What notable skin colorations do
you see?
Do you see a pattern in the fish’s coloration?
If so what purpose might that pattern have to the ecology of the fish?
Next, you'll need to identify the fins: Caudal, Pectoral, Pelvic, Anal, Dorsal, and Adipose (only on some
fish). Also, identify the claspers on the dogfish (if present). Use the diagrams below as a guide to identify
these fins.
Note that fins consist of rays (Teleostei only; white perch) projecting from the body which are typically
connected by a membrane. The number of rays on the fins is often an important characteristic in fish
identification. Practice counting the number of dorsal fin rays and anal fin rays.
How many rays does the white perch have on its anal fin?
How do the dorsal fins on the lamprey and shark differ from the white perch?
Find the following structures on the lamprey (use the diagrams below as a guide to identify these
structures).
Pineal Eye
External Gill Slits
Leaflike Lamellae
Cloaca
Buccal Funnel
Horny teeth
Nostril
Find the following structures on the dogfish (use the diagrams below as a guide to identify these
structures).
Spiracle
Fin Spine
External Gill Slits
Zoology 511
Spring 2006
Find the following structures on the white perch (use the diagrams below as a guide to identify these
structures).
Operculum
Maxilla
Pre-maxilla
Branchiostegal Rays
Anus
Nares
Gills
Scales
Caudal Peduncle
Lateral Line
Look at the lateral line of the white perch under a magnifying glass. Remove a lateral line scale and look at
it under a dissecting scope, and reexamine the lateral line where you removed the scale. What does the
lateral line consist of? What do you suppose its function is?
Remove some white perch scales (from somewhere other than the lateral line) and examine them under the
dissecting scope. Draw a picture of one:
Examine the gill area of the white perch. Lift and then lower the opercula; do any other structures move
away from the main body of the fish? Which ones?
Distend, or stretch the lower jaw of your perch. Notice how flexible the skin is on the posterior edges of
the maxilla-premaxilla process. Put your finger inside the perch’s mouth. On what surfaces do you feel
some kind of dentition?
Internal Anatomy (dogfish, white perch)
Caution - your scalpel blade is extremely sharp. Take time to check the location of all your fingers
before you start an incision!
Observe the prepared dissection of the dogfish and identify these internal structures.
Esophageal Papillae
Rugae
Pancreas
Rectal Gland
Rectum
Ileum
Pylorus
Gall Bladder
Liver
Stomach
Spleen
Colon
Spiral Valve
Duodenum
Common Bile Duct
Notice the size and oiliness of the dogfish liver. The oil is called squalene and hence the scientific name of
the dogfish (Squalus acanthias). Can you think of an additional function of the dogfish liver besides its
normal function, considering its size and oiliness?
Zoology 511
Spring 2006
What purpose does the spiral valve have in the intestine of the dogfish?
Before you begin any incisions on the white perch, weigh the fish.
Expose the oral cavity and pharynx of the white perch by making a shallow horizontal cut from the
posterior corner of the mouth to the posterior edge of the operculum. Be careful not to cut through the gill
membranes beneath the operculum. For the white perch, it is easiest to use scissors to cut through the
operculum.
Identify the gill arches, gill filaments and gill rakers. Any ideas on the function of the gill rakers??
(Take an entire gill arch out and look at it under the scope for a closer look.)
Expose the abdominal cavity and pericardial cavity of the white perch: first, gently descale the ventral
surface of the fish, and then make a shallow longitudinal incision extending from the anus to between the
gill arches. You’ll need to use scissors to get through the pelvic fin girdle. Now, make a vertical cut from
the anus to the lateral line, and another vertical cut from the abdominal cavity along the posterior edge of
the operculum. The abdominal cavity is lined by a thin membrane called the peritoneum.
Identify the following features:
Heart
Stomach
Liver
Intestine
Kidney
Gonads
Fat deposits
What sex is your fish?
The gonadosomatic index (GSI) is the ratio of the gonad weight to the fishes’ total weight. Remove the
gonads from your fish. At the front of the class is a scale. What is your fish’s GSI?
Now, make an incision parallel to and dorsal to the first cut, so that one half of the left side of the fish is
now exposed. This should give you a good view of the gas bladder (may not be visible, but look for the
cavity anyway).
Zoology 511
Spring 2006
On the other side of your fish, starting at the caudal peduncle, delicately cut under the skin. You want to
remove the skin (not just the scales) and expose the muscle tissue. Continue up to the opercle or as far as
you can, being careful to remove the skin only.
Try to identify these tissues (use the diagrams below as a guide):
Hypaxialis
Epaxialis
White muscle tissue
Red muscle tissue
If you have time, try to shave away muscle from the area around the spine to expose the vertebrae; do this
near the abdominal cavity AND at the caudal penduncle. There are two different kinds of vertebrae in a
fish: abdominal vertebrae and caudal vertebrae. What differences do you notice between them?
Using a probe, see if you can locate the hemal and neural canals on a caudal vertebra.
Deposit your fish and its parts in the trash can at the front of the room. Wipe down your lab bench, rinse
off your instruments, and wash your hands well.
QUESTIONS (Answer in one or two short sentences and turn in next week)
1. Answer these statements TRUE or FALSE about the white perch you dissected today:
a.
b.
c.
d.
The pelvic fins are ventral relative to the pectoral fins.
The caudal fin is located anterior relative to the dorsal fin.
The anal fin is located posterior relative to the caudal fin.
The dorsal fin is dorsal relative to the lateral line.
2. Sharks and rays (chondrichthyes) possess a series of gill slits through which water is passed. In
contrast, perch possess a more elaborate gill anatomy consisting of the operculum and brachiostegal rays.
Speculate how the presence of the operculum and brachiostegal rays enhance respiration for teleost fish.
3. How would you expect the gill rakers of a planktivore (plankton-eater) to differ from those of a
piscivore (fish-eater)? Why?
Zoology 511
Spring 2006
Fish Anatomy Diagrams
The following diagrams will help you identify external and internal structures of fishes.
Below is a picture of a snook (Centropomus undecimalis), from McClane (1978). Use it
for help with external anatomy.
Pictured at right is a
typical salmonid, taken
from Cailliet et al.
(1986).
Zoology 511
Spring 2006
Below is a picture of the musculature of a salmonid. Figure taken from Cailliet et al.
(1986).
Below is a picture of two vertebrae: a) abdominal vertebra; b) caudal vertebra. From
Cailliet et al. (1986).
Zoology 511
Spring 2006
Below is a picture of the arrangement and structure of gill rakers and gill arches of a bony
fish (Cailliet et al. 1986).
Below is a diagram of the external anatomy of the Pacific lamprey (Lampetra tridentate)
taken from Cailliet et al. (1986).
Zoology 511
Spring 2006
Below is a diagram of the internal anatomy of the Pacific lamprey (Lampetra tridentate)
taken from Wessells and Center (1975).
Below is a diagram of the external features of the spiny dogfish (Squalus acanthias)
(Miller and Lea 1972).
Zoology 511
Spring 2006
Below is a vental view of the internal anatomy of the spiny dogfish (Squalus acanthias)
(Wischnitzer 1972).