Minnows, carps, loaches, and their relatives – known as Cypriniforms – are an exceptionally diverse group of fishes (4,182 currently valid species according to the Catalog of Fishes) that come in a wide range of sizes, shapes, and colors . Their overall small size and aesthetic variation has made them appealing to the aquarists (does the clown loach [Chromobotia macracanthus] look familiar?)! In fact, aquarists are some of the most knowledgeable people on these species!
Just as interesting is that Cypriniforms can be found across multiple continents in a variety of habitats with unique foraging, locomotive, and reproductive patterns and morphologies and fill a variety of ecological roles (e.g., predatory and prey). For example, the fathead minnow, known scientifically as Pimephales promelas (Check out this blog post by Liz Marchio for an excellent explanation of scientific names!) develops excessively large tubercles on a really dark, swollen head during the breeding season (see some images here). There are THOUSANDS of other interesting species. Just hit up Google and start searching!
As an evolutionary biologist, I am interested in understanding and conserving patterns of phenotypic diversity and novelty: How did what’s here get here and how can we keep it here? I think the best approach is to look at what we know about Cypriniform diversity and what we know about the evolution of that diversity, first. That is, how are those 4,182 species distributed across groups and how are those groups related to each other. Accordingly, I am splitting “my first blog post” into a three-part series. Part I will provide insight into what a Cypriniform is and the distribution of species across families. Part II will focus more on each family and what makes a Cobitid a Cobitid and a Cyprinid a Cyprinid. Part III will then focus on the evolutionary history of this group, how the families are related to each other, and what the implications are for the evolution of Cypriniform diversity! After that, my goal is really to blog about anything I find interesting for minnows – recent research using a particular minnow species, a pretty new species I saw at a pet shop, an update on the taxonomy of a particular group. Really, pretty much anything Cypriniformish.
First, what is a Cypriniform? I’m sure you think this should be an easy question to answer, right? It’s a small fish that goes in my aquarium…or that I see at the edge of the lake…or…OK, not really. It is actually difficult to answer this question in a way that makes most people go “aha, I understand!” Given this problem, let’s stick with defining a Cypriniform as any fish with a kinethmoid. What?!?!? OK, the kinethmoid is a tiny bone used in jaw protrusion (e.g., eating) and is found only in species that are considered Cypriniforms. Makes sense, right? What does it look like? Check out this photograph:
This photograph is a dorsal view – standing over the fish and looking down on its mouth – of the the jaw bones from a cleared-and-stained specimen of Homaloptera ripleyi (from Ott 2009). The five bones labelled are the maxillary (Mx), premaxillary (Pmx), anterior process of prexmaxillary (anP), ascending process of the premaxillary (asP), and the, wait for it…kinethmoid (Ke)! It may take some Googling and a brief review of your anatomy to identify each of these bones and understand the kinethmoid, but now you know the kinethmoid is a legitimate bone in Cypriniforms (read more in Staab et al. 2012). For the future purpose of this blog, we will assume that any species classified as a Cypriniform is appropriately classified and has a…kinethmoid!
Now, let’s look at the distribution of that diversity, taxonomically speaking. Although still debated and it may change, there are currently 11 recognized families of Cypriniforms according to the Catalog of Fishes (listed in no particular order):
- Cyprinidae (2960 species)
- Psilorhychidae (24 species)
- Cobitidae (245 species)
- Balitoridae (230 species)
- Nemacheilidae (627 species)
- Serpenticobitidae (3 species)
- Vaillantellidae (3 species)
- Ellopostomatidae (2 species)
- Barbuccidae (2 species)
- Gryinocheilidae (3 species)
- Catostomidae (83 species)
There are a few quick observations that we can make here:
- The family Cyprinidae is exceptionally diverse relative to all other families of Cypriniformes. This family is an order of magnitude larger than the diversity in all other families. The next most diverse family contains only 627 species (Nemacheilidae), only 15% of the diversity observed in Cyprinidae!
- The disparity of taxonomic diversity is unusual. There is one exceptionally diverse family (Cyprinidae), four families with moderate diversity (Cobitiidae, Balitoridae, Nemacheilidae, Catostomidae), and six families with low diversity (Psilorhynchidae, Serpenticobitidae, Vaillantellidae, Ellopostomatidae, Barbuccidae, Gyrinocheilidae). It’s an unusual pattern worth exploring more.
What do you think? Are there any patterns about the distribution of diversity in this order that you notice? Next time, I will focus on what species in each of these families look like and provide some information about each of these groups!
Ott, G. 2009. Redescription of Homaloptera ripleyi (Fowler, 1940) from Sumatra, Indonesia (Teleostei: Balitoridae). Bulletin of Fish Biology 11(1/2):73-86.
Staab, K. L. 2012. Comparative kinematics of cypriniform premaxillary protrusion. Zoology 115(2):65-77.