Playing with a bluegill. During spawning season they get defensive around their nests.

"Like other sunfish, bluegills build nests in colonies which range from just a few nests to a hundred or more. The colonies are located in shallow water with a gravel, sand or hard mud bottom. The male uses his tail to sweep a circular area up to a foot in diameter and two to six inches deep.

He then swims in circles around the nest and grunts to attract a female. Once the eggs are laid and fertilized, they sink to the bottom of the nest. A female bluegill can produce up to 60,000 eggs, depending on her age and size. The entire colony spawns on the same day, and the process may take anywhere from 6 to 12 hours. A male may attract more than one female to his nest and a female may deposit eggs in more than one nest.

Once spawning is complete, the female leaves and the male is left to guard the nest. He fans the eggs with his pectoral fins to prevent siltation and guards them from predators, which include other bluegills. Given that the nests are very close to one another, a male bluegill is apparently able to distinguish a potential intruder from a neighbor. The eggs hatch in 2 to 5 days. The yolk sac fry cannot swim but remain hidden on the bottom of the nest, and the male continues to guard them for another 5 to 10 days."

• https://dnr.maryland.gov/ccs/Documents/education/Biology-of-Bluegill.pdf