Oncorhynchus mykiss

Rainbow Trout Anatomy A Study and Dissection Guide.

TroutDissection.dnr.sc.gov Adapted by Joyce Plyter 2013

NOTES: A. You will need a copy of the “Trout Book” with internal organs.B. On your copy, circle the name of each underlined part that you find in the trout.

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Name_____________________

Date___________________

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External Anatomy

HeadTrunkTail

The slim shape, and smooth scale covering of fish help them swim through the water.

1. Examine the scales that cover and protect the fish. They grow as the fish grows. Each growth spurt will show on the scales as a “ring” or ridge. There will be several rings each year.

2. Use a microscope to view the growth rings of a scale.3

Fins

Pelvic FinsPectoral Fins

Adipose Fin

Caudal or TailFin

Dorsal Fin

The caudal fin or tail fin provides the “push” for the trout to start moving and also acts as a rudder for steering.

Anal, adipose and dorsal (top) fins are used for swimming and balance.

The pectoral fins act as brakes and turn left and right.

3. Find each fin. The adipose fin is often clipped in hatchery fish.

The pelvic fins help the fish move up and down.

Anal Fin

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Sense Organs

Scales

The lateral line runs from the head of the fish to the tail. It detects vibrations or waves in the water. This helps keep the trout from bumping into things and helps sense danger.

The operculum is a hard plate that covers the delicate gills.

The pupil of the eye is slightly triangular in shape which helps the trout see above, in front and below, but each eye only sees on its side.

Trout use their mouths to grab food, bring in water and to feel things.

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Lateral Line

Eye

Operculum Mouth

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Eye Lens

Trout can see things both near and far away. The large pupils let as much light as possible enter the eye. The eye needs no lid, as it is always in water.

The eyes are placed so they work separately. Our eyes work together, which give us depth perception.

4. Make some “Trout Goggles”. Ask for the pattern or place a “blinder” on your head between your eyes to force each eye to work separately. Try walking, writing and talking to someone.

The lens in the eye moves around and allows fish to focus on objects.

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Mouth

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Nostril or Nare

Teeth

The nare is a closed sac. It helps the fish to smell odors.

Teeth are found along the upper and lower jaws. They grasp and hold onto prey.

5. Open the mouth. Find and touch the teeth. Check the jaws, roof of the mouth and even the tongue for teeth. Think about trying to get your finger out if the trout clamped down. The teeth are for holding, not chewing. Trout swallow their food whole.

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MouthGill rakers strain particles out of the water to keep the gills from getting clogged and injured.

Food passes through the esophagus to the stomach.

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Gills

6. Pull back the operculum to show the gills. Find 4 layers.

Operculum

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Gills

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Gill filaments Gill arch

Water is taken in through the mouth and passes over the gills. The blood in the gills take oxygen (O2) from the water and release carbon dioxide (CO2). Body cells need O2 to burn food.

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7. Read all of this page before you start. Using the line above for a guide, use dissecting scissors to cut a flap of skin and muscle so you can see the internal organs.

Start at the vent opening. Cut through skin and muscle, checking as you go. You need to get into the body cavity, but not so deep as to cut organs. Pull the flap down, but leave it attached.

Internal Anatomy: The Dissection

Start

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8. Match the “Trout Book” “paper organs” with each actual organ of your trout as you work. Color each paper organ to match the actual organ.

9. As you find an organ, use a flap of tape at the top of the colored paper organ to attach it to your “Trout Book”. Match the trout. Using a flap of tape lets you lift each organ to see what is under it.

Trout Book: A Paper Trout

Start

Internal Anatomy

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SpleenGall bladderLiverHeart Kidney

Pyloric caecaStomach

Swim bladder

A female has ovaries that produce eggs along the kidney. It may or may not have eggs. A male will have a testes that produces male sperm cells.

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Kidney

The kidney filters waste from the blood stream and also makes blood. Two canals carry waste from the kidneys to the bladder, an almost clear storage bag.

From the bladder, the liquid waste passes to the outside through a hole called the vent.

Kidney

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Swim BladderThis is an inflatedswim bladder.

The swim bladder is like an adjustable balloon or life jacket. It allows the trout to float and move up and down in the water. To fill the swim bladder, fish gulp and swallow air. Fish “burp” to get air out of the swim bladder.

10. If the swim bladder is empty, use a clean straw to fill the swim bladder with air. You may need to remove it from the fish.

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Digestion

Fat IntestineStomachs:

11. Use your straw to trace the pathway of food from the mouth through the esophagus to the stomach. 16

Path of DigestionMouth

Esophagus

Cardiac stomach

Pyloric stomach

Inte

stin

e

When a trout eats, both food and water enter the mouth.

Water is directed to the gills, and food goes to the esophagus which leads to the stomach. Food moves through the stomachs into the intestines as it is digested. Most of the digested food is picked up by the blood (absorption) at the pyloric stomach (caeca). The intestine does some digestion and absorption and then undigested substances move out the vent (anus).

Vent

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First or Cardiac Stomach

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Digestion of food starts in the cardiac stomach or first stomach. Food is swallowed whole. Acid and enzymes are added to digest protein. Muscles squeeze and mix. If your trout just ate, there may be food in the stomach. It is a carnivore, so eats other animals.

12. Cut the stomach, starting at the lower end. Cut toward the mouth and then look inside to see if and/or what it ate.

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Second Stomach: Pyloric CaecaThe pyloric caeca (see-ka) act like our small intestine. They release digestive juices that break down food to liquid. Liquid food (nutrients) go into the blood stream here (absorption) and at the intestine .

Our small intestine is long and curled around in our abdomen. The long trip gives the food time to digest and go to our blood stream.

Pyloric caeca

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Liver and Gall Bladder

The liver filters the blood and produces bile which is stored in the gall bladder. Bile breaks down (digests) fat.

The gall bladder is connected to the liver and stores bile made by the liver. It is a thin storage bag and may be greenish in color.

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GallBladder

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Spleen

The spleen makes and stores blood cells.

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Heart

VentricleAtriumBulbus arteriosus22

Heart

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Ventricle

Atrium

Bulbus arteriosus

The heart consists of two chambers, the soft atrium that receives the blood and the muscular ventricle that pumps the blood to the body.

The blood first passes through bulbus arteriosus to the gills where it picks up oxygen, then circulates through the body to the organs where nutrients, gases and wastes are exchanged.

Valves keep the blood from going backwards. A valve is a one-way gate. When the ventricle squeezes (pumps), the blood has to go toward the gills because the “gate” to the body (where the blood came into the heart) is closed.

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Brain The brain is the control center of the fish. All sensory information is processed by the brain. Automatic functions (such as breathing) and higher behaviors ("Should I eat that critter ?") happen in the brain.

The olfactory lobes, for smell and taste, are located inside the nostrils of the fish and are connected to the brain by olfactory nerves.

The large optic lobe is used for sight and the cerebellum in the rear coordinates and regulates muscle activity. The spinal cord exits the rear of the brain and passes through the vertebrae, which gives it protection. Signals from the lateral line go to the brain along the spinal cord.

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To spinal cordCerebellum

Optic lobes

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www.classroomaquarium.org.

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Trout Anatomy Poster by Ed Huff

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