ZOO 511
Lab #1 Handout
Introduction: TA and Class Introductions and Course overview – Syllabus
Lecture: Definitions and External and internal anatomy
Skills Development: Parts of scientific paper – intro and Searching the primary literature
Goals:
Define various fish related terms used in both lab and lecture
Acquire basic understanding of the internal and external anatomical structures of fish
All 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. We’ll look at a number of different species in lab.
Make sure to do all your dissections carefully so other groups can examine you fish when you are done.
Which fish are you examining (Circle)? : Bluegill, white perch, crappie, yellow perch, rock bass
In the field, the coloration of fish can be important to their identification. What notable skin colorations do
you see on your particular fish? Do you see a pattern in the fish’s coloration?
If so what purpose might that pattern have to the ecology of the fish?
Sketch you fish carefully and to identify the fins: Caudal, Pectoral, Pelvic, Anal, Dorsal, and Adipose (only on
some fish). Sketching is an important component to recognizing features because it makes you look carefully
at the different characteristics of the fish. Use the diagrams at the end as a guide.
Note that fins consist of rays 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 your fish have on its anal fin? What about the dorsal fin?
Find the following structures on your fish
Operculum
Maxilla
Pre-maxilla
Caudal Peduncle
Anus
Nares
Gills
Scales
Lateral Line
How many scales does your fish have in the entire lateral line? (A pain but useful exercise)
ZOO 511
Lab #1 Handout
Remove a lateral line scale and look at it under a microscope, 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 scales from the brown trout at the front of class, draw a picture of your fish scale and the
brown trout scale
Examine the gill area of your fish. 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 fish. Notice how flexible the skin is on the posterior edges of the
maxilla-premaxilla process. Think about how the fish uses its mouth for both breathing and feeding, what
attributes of the mouth and operculum do you think help it with these processes?
Internal Anatomy
BE CAREFUL WHEN USING SCALPELS, SCISSORS, OR PROBES
Before you dissect the fish, write down the species, total length (mm), and weight (g) of your 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. It may be easiest to use scissors to cut through the operculum.
Identify the gill arches, gill filaments and gill rakers. How long are the gill rakers on your fish? Go around
the room and look at the gill rakers on the other fish species at different tables, how does your fish
compare?
Expose the abdominal cavity and pericardial cavity of your fish: first 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. The picture of the white perch on the board is how you fish should look
after these cuts.
Identify the following features:
Heart
Stomach
Liver
Intestine
What sex is your fish?
Kidney
Gonads
Fat deposits
ZOO 511
Lab #1 Handout
The gonadosomatic index (GSI) is the ratio of the gonad weight to the fishes’ total weight. Remove the
gonads from your fish. At the back 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).
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 diagram at the end as a guide):
Hypaxialis
Epaxialis
White muscle tissue
Red muscle tissue
QUESTIONS
1. Answer these statements TRUE or FALSE about the fish 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. How would you expect the gill rakers of a planktivore (plankton-eater) to differ from those of a piscivore
(fish-eater)? Why?
3. Pick one external feature and one internal feature and describe how you think this particular structure
might influence the ecology of the fish. Its ok to guess here if you don’t know, the point is to think about
fish and factors that influence its abundance, distributions, or interactions. (ie. The white perch does not
have large sharp teeth suggesting it doesn’t eat the same things as the pickerel)
ZOO 511
Lab #1 Handout