Fish
Bluegill
Lepomis macrochirus · also called bream, brim, sunny
The bluegill is the fish on the end of the line in a thousand childhood photographs — a flat, palm-sized, olive-and-orange sunfish pulled off a dock on a summer afternoon. It is also, when you look closely at its breeding beds, a small masterpiece of evolutionary strategy.
Overview
Lepomis macrochirus is native to central and eastern North America and stocked almost everywhere else. It is a round, flattened, hand-sized fish with a small mouth and a solid black gill flap, and it eats insect larvae, plankton, and small crustaceans. It is the fish most North American anglers catch first.
The breeding colony
In late spring, males sweep dozens of nests side by side in the shallows and guard the eggs. Those nests are the stage for three kinds of male: big nest-building parental males that take years to mature, fast-maturing sneaker males that dash in to spawn, and satellite males that look and act like females to get onto a nest. One nest can hold young from several fathers.
An imperial mistake
In 1960 the future Emperor of Japan was given 15 bluegill by Chicago’s mayor. Their descendants became a damaging invasive in Japanese lakes — something the Emperor later publicly regretted.
Status
Least Concern and hugely abundant in North America; a problem only where it has been introduced abroad.
Bluegill: common questions
Why is the bluegill such a common first fish?
Several things line up. Bluegill live nearly everywhere there is warm, still or slow fresh water, including farm ponds, park lakes, and reservoirs, so a beginner rarely has to travel to find them. They are numerous, they feed actively for much of the day, and they will readily take a piece of worm, a small jig, or a bit of bread on a simple hook and bobber. They fight hard for their size, turning sideways to use their flat body against the line, which is fun on light tackle. And they are good to eat. For generations of North American children, catching a bluegill off a dock has been the introduction to fishing.
What are the different kinds of male bluegill?
Bluegill males follow one of two life plans, and one of those has two versions. Most males become "parental" males — they take about seven years to mature, grow large, and, in the breeding season, dig a nest, court females, and guard the eggs and young. A minority become "cuckolder" males — they mature in about two years while still small, do not build nests, and instead fertilise eggs on other males' nests, either as "sneakers" that make a quick dash through the nest at spawning or as "satellites" that are coloured and shaped like females and are allowed to hover on the nest before slipping in. The result is that a single guarded nest often contains offspring sired by two or three males.
Is a bluegill the same as a bream or a sunfish?
In North America, "bream" or "brim" and "sunny" are informal names for the bluegill and its close relatives, so someone in the southern US saying they caught a mess of bream usually means bluegill and similar sunfish. Confusingly, "bream" in Britain and Europe refers to entirely different, unrelated carp-family fish. The bluegill is one species in the sunfish family, Centrarchidae, which also includes the pumpkinseed, the redear, the green sunfish, and the much larger black basses. All the small colourful ones are loosely called sunfish or panfish.
Why did stocking bluegill in Japan become a problem?
Bluegill in a Japanese lake behave like any well-adapted introduced predator with no local checks. They eat the eggs, larvae, and food of native fish, they compete with native species for the same insects and zooplankton, and they breed prolifically, so within a few decades of the 1960s introduction they had become one of the dominant fish in Lake Biwa and other waters, contributing to steep declines in native species. The bluegill is now listed as an invasive alien species in Japan with restrictions on keeping and releasing it, and it is a standard example of how a small, familiar sport fish can do serious damage outside its home range.