Fishes of Wisconsin: Attack of the Clones

Happy Fish Fry Day! Once again fish is on the menu here at the CFL blog (and just about every restaurant in Wisconsin). Today we’re continuing the epic slog through all of the images on the Fishes of Wisconsin poster and we’re sticking with small plates. In fact, it’s a two-course deal. Introducing, the finescale dace and the northern redbelly dace.

Photo: Marilyn Larsen
Photo: Marilyn Larsen

Many anglers many know finescale dace (Chrosomus neogaeus) and northern redbelly dace (Chrosomus eos) as relatively hardy kinds of bait fish, which likely has readers of this blog groaning “Not again! TWO tiny fishes? Didn’t we have a boring little minnow last time?”
Photo: Marilyn Larsen
Photo: Marilyn Larsen

Well, yes, yes we did.
But the fact that no one came to the defense of the bullhead minnow’s reputation doesn’t discount the following facts:

  1. Dace aren’t minnows.
  2. Minnow” does NOT mean “little fish.”
  3. When it comes to reproduction, when the finescale dace meets a northern redbelly dace, something crazy happens.

First, take a look at these distribution maps the USGS has created for each species.

Maps show where northern redbelly dace (top) and finescale dace (bottom) are commonly found. Image: USGS
Maps show where northern redbelly dace (top) and finescale dace (bottom) are commonly found. Image: USGS

You’ll notice significant overlap in areas where Northern Redbelly Dace (top) and Finescale Dace (bottom) hang out. What’s more, they both like shallow parts of lakes, sluggish pools of small rivers and, notably, beaver ponds, which means they see a lot of each other. Which means, well, relations between the two species have developed. And this makes for a fun fishy fact for your Fish Fry Day.
Due to their overlapping ranges and similar habitat preferences, it is not uncommon for finescale and northern redbelly dace to dart into the same mass of filamentous algae during the chaos of spawning and release a cloud of eggs and sperm. The result of this unintentional mating is a hybrid species of fish that’s part finescale, part northern redbelly, and ALL female.
While this video below is of Southern redbelly dace spawning, it paints the picture – it’s not exactly a, um, particularly specific enterprise:

While It’s common in the life aquatic to find hybrid species of fish, they are most often sterile – the end of the road, genetically. But in the case of the dace, their hybrids are all-female clones, equipped with identical eggs and a unique reproductive strategy called “gynogenesis.” In gynogenesis, all that’s needed to start egg development is the presence of sperm from the male of a sexually mature related species. The catch is that that single spermatozoa only kick-starts development. It doesn’t help guide it. That’s right, none of the male genetic material is incorporated into the egg – the egg simply “grows up” to become another genetically identical female and the cycle repeats. In fact, researches have found habitat in Minnesotan lakes and streams populated by genetically identical schools of hybrid dace.
That’s right – instead of the usual genetic dead end of sterile hybrids, the finescale and northern redbelly parents that started the whole process in motion may eventually be replaced by an army of hybrid clones!
Sigh….they grow up so fast.