Fish Fry Day – Bluegill (x3)

Happy Fish Fry Day! Here in Wisconsin, we’re putting cod, perch, and walleye on the menu and, here at the blog, we’ve got fun facts about native fish.
Today’s special: bluegill, three ways.

Photo: Wisconsin Sea Grant Institute

Bluegill aren’t exactly a rare species. In fact, they’re often the first fish kids learn to catch and, as any avid fisherman can tell you, they sure are tasty! But we’re here to talk about something you don’t know and, today, that’s a look at the secret (and sordid) sex life of bluegill.
Ted Bier gives tips for Fish IDs at CLA's "Yahara 101" event. Photo: A. Hinterthuer
Ted Bier gives tips for Fish IDs at CLA’s “Yahara 101” event. Photo: A. Hinterthuer

Just yesterday morning, Ted Bier, a senior research scientist with the Long-Term Ecological Research program here at the CFL gave a talk at the Clean Lakes Alliance‘s monthly Madison-lake education series, “Yahara 101.” While Ted talked about fish from brook silverside minnows to hybrid tiger muskies, it was the little old bluegill that caught my attention. And that’s because, at any given time, there are THREE different kinds of male bluegill in our lakes. And it all has to do with how they pass on their genes.
For a much more comprehensive read on this, may I suggest “The Secret Life of Bluegills,” by Dr. Dave Willis from South Dakota State University. But, here’s the lowdownl:
Like some other fish species (bass, for example) bluegill males build nests when spawning season rolls around. They clear out circular depressions in the sand or cobble and then wait for an interested female to swim by and deposit her eggs. These nests are usually close to lots of other nests, forming a colony. “Dominant” males get the prime real estate and, once the female has done her job, the male fertilizes the eggs with his milt, then guards the eggs and (for a short while) even guards his newly hatched progeny. Sounds simple right?
A male bluegill (far right) mimics his female counterpart (center) in an attempt to add his genes to the pool. Photo: Dr. Bryan Neff, University of Windsor, Ontario
A male bluegill (far right) mimics his female counterpart (center) in an attempt to add his genes to the pool. Photo: Dr. Bryan Neff, University of Windsor, Ontario

The problem is, there are two other types of males out there. Both are called “cuckold” males. One is a “female mimic.” This guy adopts the approximate size and coloration of a female and sidles up next to her while she’s on some big bluegill’s nest and deposits HIS DNA (in the form of milt, of course) before the big guy can do the deed. The “dominant” male assumes he’s landed not one, but two potential mates and rarely even chases the “mimic” away.
As if fake females weren’t enough, “dominant” males also have to look out for “sneakers.” “Sneakers” are even smaller males that, essentially, wait for the right moment and, right after the female leaves her eggs and the “dominant” male is about to fertilize them, dart in and beat him to the punch.

Whichever of the three males is successful, his offspring are going to be “dominant,” “sneakers,” or “mimics,” just like dear old Dad. It’s a fascinating evolutionary behavior that lets the little guy throw some of his genetic code in the gene pool, but it has all sorts of implications for fisheries managers. If fishermen catch and keep only the biggest bluegill, are they helping the little guys fill their lake? Can “dominant” males tell which offspring are their own and which are the imposters? Some researchers have observed selective dining on young fry.
While the experts try to sort this all out, we think it’s pretty cool that such a common fish can have such an unusual life history. We’ll tuck in to a different species next week. Until then, Happy Fish Fry Day!

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