Fish Anatomy and Adaptations

In this lesson, we will explore the internal anatomy of the largemouth bass (Micropterus salmoides). We will also define and discuss adaptations through an evolutionary lens.

What is anatomy?

Anatomy is the study of the bodily structure of living organisms. Fish anatomy is the study of the bodily structure of fish.

Internal (inside) anatomy helps us better understand the common internal features and functions of an organism.

What is a dissection and why is it important?

A dissection is a scientific procedure whereby a preserved organism is opened up, usually with a scalpel or similar bladed instrument, for the purpose of studying its internal anatomy. Dissections occur in a laboratory setting.

Dissections allow us to explore and better understand the internal workings of various organisms.

Largemouth bass (Micropterus salmoides), pictured above

Species Profile: Largemouth Bass

The largemouth bass (Micropterus salmoides) is a freshwater gamefish in the sunfish (Centrarchidae) family. Largemouth bass are not native to the District of Columbia; however, many anglers target them for catch-and-release due to their tenacious fight. Follow along as we explore the internal anatomy of the largemouth bass!

Virtual Dissection

Using our "dissected" specimen on the right, we will locate and define the internal anatomical structures of the largemouth bass. The internal structures that we will define are common across most bony fish.

Brain

The brain acts as the control center of the fish. It is the site of all sensory processing and decision making.

Spine

The spine is the primary structural framework upon which the fish's body is built. It is comprised of vertebrae (spinal columns) which house and protect the spinal cord.

Spinal Cord

The spinal cord is a long, thin, tubular structure made of nervous tissue. It relays sensory information from the body to the brain and instructions from the brain to the body.

Heart

The heart circulates blood throughout the body, delivering oxygen and digested nutrients to the cells of various organs and removing wastes for delivery to the kidneys and liver for elimination.

Liver

The liver serves multiple roles. It secretes enzymes that aid in digestion, acts as a storage area for fats and carbohydrates, breaks down old blood cells, and aids in nitrogen excretion.

Gallbladder

The gallbladder stores bile that is created by the liver. Bile aids in the digestive process.

Spleen

The spleen is a non-vital organ that acts as a blood filter. The spleen also plays a role in the fish's immune system.

Kidney

The kidney acts as a filter for liquid wastes from the blood. The kidney also plays a key role in osmoregulation, or the regulation of water and salt in the fish's body.

Swim Bladder

The swim bladder is a hollow, gas filled organ that helps maintain neutral buoyancy, allowing the fish to suspend in the water. This helps the fish conserve energy.

Stomach

The stomach aids in the temporary storage and digestion of food.

Pyloric Caeca

The pyloric caeca, located near the stomach and intestines, secretes enzymes that aid in digestion.

Intestine

The intestines aid in the break down and absorption of critical nutrients.

Gonads

The gonads serve as the fish's reproductive organs. The eggs of a female largemouth bass are pictured above.

Urinary Bladder

The urinary bladder stores excess waste fluid. Most nitrogenous waste is eliminated via the gills of the fish.

Vent

The vent is the site of waste elimination from the fish's body. The vent also allows the fish to release eggs or sperm via the genital tract.

Anatomy Quiz

Test your new found internal anatomy knowledge with this timed quiz from Purpose Games!

Scale and Otolith Analysis

Scales and otoliths, or ear bones, can be used to determine both the age and origin of fish.

Read this brief article from VIMS to learn more about how scientists use scale and otolith analysis determine the age and origin of American shad, the District of Columbia's State Fish. Once you've read the article, test your knowledge with the quick quiz below.

Fish otolith, pictured above. Note the concentric rings.

Quick Quiz

Name the method scientists use to determine the age of American shad based on their scales.
Scales are removed from the area just below which fin on the American shad's body?
Name the chemical that scientists use to mark the otoliths of hatchery reared American shad.
How do scientists determine which river system an American shad was stocked in?

Adaptations

In the field of evolutionary biology, adaptations are characteristics that better allow an organism to survive and reproduce in its natural environment. Adaptations can be structural, behavioral, or physiological.

Take the example of the northern snakehead (Channa argus) , a non-native invasive species now found in the waters of the District of Columbia. Snakeheads have long, torpedo-like bodies that allow them to swim at high speeds through open water to chase down prey. Snakeheads are fry guarders, meaning they actively guard their offspring from potential predators. Snakeheads are also capable of breathing atmospheric oxygen (air) directly.

These three characteristics are examples of structural, behavioral, and physiological adaptations, respectively.

Northern snakehead (Channa argus), pictured above

Adaptation Activities

Test your adaptation knowledge by reading this article on the longnose gar (Lepisosteus osseus) from our friends at the Chesapeake Bay Program.

Once you've completed the article, brainstorm three advantageous adaptations that might help the longnose gar survive in our local waters.

Longnose gar (Lepisosteus osseus), pictured above

To learn more about the adaptations of fish found in District waters, check out our Fashion a Fish Activity on Google Jamboard!

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