Bluegills Are Adapted for Success in Our Waterways

Bluegills, Lepomis macrochirus, are one of the most common fish around. They are found in freshwater streams, rivers, lakes, ponds and wetlands throughout Illinois, and even as far west as the Rocky Mountains.

(Photo via Shutterstock)

Bluegills are so common and popular that they have earned the special recognition of being chosen as the state fish of Illinois. They are able to keep their population numbers high because of some interesting adaptations.


Hide and seek


As far as fish are concerned, bluegills are on the smaller side. They average 6 inches long and weigh about a half-pound. Because of their small size they can live in shallow or deep water. They are also able to hide in a lot of places, like among underwater plants and inside or around fallen logs. It’s a lot harder for predators like snapping turtles, herons and larger fish to eat bluegills if they can’t find them!


Fin-tastic!

Notice the spiny front of the bluegill’s dorsal fin. (Photo via Shutterstock)

Even if a bluegill does get spotted by a predator, it has a good chance of escaping! That’s because bluegills are really fast swimmers! They have different types of fins that work in different ways to help them move through the water. Let’s take a look at their different kinds of fins:

  • Pectoral fins are the pair of fins on either side of the bluegill’s body. These fins help with stopping, turning and moving up and down. Bluegills’ pectoral fins are on an angle, which provides extra-quick turning abilities, and they are large and flexible, which helps them stop quickly. So if they can sense a predator approaching, they are able to stop and change directions quickly, possibly confusing the predator, or at least getting out of the way of a bite!

  • The dorsal fin is the large fin down the center of a bluegill’s back. This fin provides balance and helps keep the fish upright instead of wobbling from side to side. Bluegills’ dorsal fins are spiny in the front, which makes them pretty unappealing to predators. Nobody wants to get a mouthful of spines!

  • The caudal fin is the tail fin. It works like the rudder of a boat and helps the bluegill steer. Bluegills’ caudal fins are slightly forked, which gives them the ability to have bursts of speed over short distances, like you moving extra fast to avoid being tagged!

All their fins working together gives them great maneuverability when trying to escape predators. It also helps them when their role switches to predator and they go after their own prey!


Eat or be eaten?


Fins help bluegills move away from their predators and toward their prey. But how do bluegills know when they are approaching?

 

Words to know

Detect: To discover or identify.

Maneuverability: Capable of being steered or directed.

Rudder: A part of a ship or boat that is used for steering.

Stealthy: Done in a way so as not to be seen or heard.

Wobble: To move unsteadily from side to side.

 

Bluegills have pretty good eyesight and rely mostly on that, but they have also adapted to have hairs in their inner ears that can detect movement in the water and even changes in pressure. So they can feel a predator approaching just by the movement of the water around them, even before they can see them. That would come in really handy in a game of tag too!


They sense prey in the same way, but how do they know if they are about to eat or be eaten? The size of the creature effects the movement of the water. Bigger creatures make bigger vibrations, and smaller creatures make smaller vibrations. Bluegills are eaten by creatures that are bigger than them and they eat creatures that are smaller.


Bluegills as predators

(Photo via Shutterstock)

Bluegills eat aquatic insects, insects that hang out on the surface of the water, and even underwater insect larvae like dragonflies and damselflies. They will even eat other fish that are smaller than them, like minnows. And yes, worms too, so try your luck at fishing for bluegills!


Bluegills are big eaters, but have very small mouths — smaller than an adult finger. But they have adapted to make up for that. They are able to extend their pharynx, or throat, and suck in their prey and the water around it, like sipping a milkshake with candy bits. They have to be very close to their prey for this to work, but their amazing fins help with their success. The only downside is if they suction a worm on a hook, they end up sucking down the hook too. Good for the fisher, but not so much for the fish!


Bluegills are more than meets the eye! They pack a lot of stealthy adaptations into their tiny bodies to help them have the speed, senses and hunting skills to not only survive but thrive here in our Illinois waterways!

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