LAB Perch Dissection

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LAB - Perch

Dissection

Introduction:

The fish in the class Osteichthyes have bony skeletons. There are three groups of the bony fish --- ray-finned fish, lobe-finned fish, and the lung fish. The perch is an example of a ray-finned fish. Its fins have spiny rays of cartilage &/or bone to

support them. Fins help the perch to move quickly through the water and steer without rolling. The perch also has a streamline body shape that makes it well adapted for movement in the water. All ray-finned fish have a swim bladder that gives the fish buoyancy allowing them to sink or rise in the water. The swim bladder also regulates the concentration of gases in the blood of the fish. Perch have powerful jaws and strong teeth for catching and eating prey. Yellow perch are primarily bottom feeders with a slow deliberate bite. They eat almost anything, but prefer minnows, insect larvae, plankton, and worms. Perch move about in schools, often numbering in the hundreds.

The scientific name for the yellow perch, most often used in dissection, is Perca flavescens (Perca means "dusky"; flavescens means "becoming gold colored"). The sides of the yellow perch are golden yellow to brassy green with six to eight dark vertical saddles and a white to yellow belly. Yellow perch have many small teeth, but no large canines. Yellow perch spawn from mid-April to early May by depositing their eggs over vegetation or the water bottom, with no care given. The eggs are laid in large

gelatinous adhesive masses.

** Do the pre-lab questions on your answer sheet.

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Materials:

Preserved perch, dissecting pan, scalpel, scissors, forceps, magnifying glass, probe(s), dissecting pins, gloves (optional), tape measure (string & ruler)

Procedure

Part 1: External

Anatomy-1. Obtain a perch & rinse off the excess preservative. Place the perch in your dissecting pan.

2. Use your tape measure (string and ruler) to determine the total length, fork length, and girth of your fish. These are shown in the diagram below.

Record these values in Table 1 on your data sheet.

4. Open the perch's mouth and observe its bony jaws. Locate the

maxilla (upper

jaw)

and the

mandible (lower jaw).

Notice which one is movable and which one is fixed.

5.

Feel the inside of the mouth for the

teeth

. Notice their position.

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7.

Open the mouth wider yet and use a wide probe to reach back to the

gill

chamber.

8. Locate the

nostrils.

9.

Locate the

eyes.

10.Find the bony covering on each side of the fish's head called the

operculum

. The opercula cover & protect the gills.

11.Use a probe to lift the operculum and observe the

gills.

12.Use scissors to cut away one operculum to view the gills. Lift the gills up and try to separate them to see their structure. Find the

gill slits

or spaces between the gills.

13.Use your scalpel to carefully cut out one gill. Find the cartilage support called the

gill arch

which holds the

gill rakers

and the soft

gill filaments

that make up each gill

.

14.

Observe the different fins on the perch. Locate the

pectoral,

anterior dorsal, posterior dorsal, pelvic, anal, and caudal fins

. Note whether the fin has spines or not

. Complete Table 2 on fins.

15.Locate the

anus

on the perch anterior to the anal fin. In the female, there are two pores (openings). The anus is in front of the

genital pore

, and the

urinary pore

is located behind the genital pore. The male has only one pore

(urogenital pore)

behind the anus.

Determine the sex of your perch

and record on your data sheet

.

16.Find the

lateral line

on the side(s) of your perch.

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Part 2: Internal Anatomy -

1. CAUTION: The scalpel may be very sharp. Use carefully and hold as shown in the picture below:

2. Use the scalpel to scrape away some of the scales in the area of the cut lines shown in Figure 4 below. Removing some of these scales will make it easier to cut into the body tissue below them.

3. Use the scalpel to make the cuts through the skin and muscle, following the lines shown in Figure 4 (where you removed the scales). Apply gentle pressure with the scalpel to get through the skin. Once you are through that tissue, it may be easier to switch to scissors for cutting through the rest of the muscle. Be careful not to damage or move any organs while cutting. Remove this section of the body wall to expose the internal organs in the body cavity.

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Once open, your fish should look similar to the pictures below. Use the pictures as a reference to find the structures in your fish, noting things like shape, size, and location to help you.

As you find structures, label them on Figure 5 in your data sheet

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4. Locate the creamy-colored

liver

in the front of the body cavity. 5. Also locate the

gall bladder

between the lobes of the liver.

6. Remove the gall bladder & liver to observe the short

esophagus

(tube) attached to the

stomach

. The stomach is a pouch-like chamber used for storing food. The stomach will have finger-like projections called

pyloric

ceca

.

7. At the posterior end of the stomach is the beginning of the

intestine

. This will be a long, continuous, coiled tube (like a hose) and should connect the stomach to the

vent / anus

.

8. Wastes exit the body through the

vent/anus

located on the ventral side of the perch.

9. Find the small reddish brown

spleen

near the stomach.

10.In the upper part of the body, below the lateral line, is the

swim bladder

. This sac has a thin wall and gives the fish buoyancy by inflating or deflating as necessary. It will have a long balloon shape and the appearance of scotch tape.

11. Below the swim bladder are the

gonads

, testes or ovaries. In a female, these

may be filled with eggs

.

Do not rupture the gonads as it will make a mess 

12.Find the 2 long, dark

kidneys

in the posterior end of the perch. These structures are used to filter wastes from the blood.

13.Return to the operculum. Below the operculum, are the bony gill rakers. 14.Using your scissors, carefully remove the gills from the gill chamber.