Photo of two three-month old male breeder Bronze Sailfin Mollies. Their gonopodia are just developing and the sailfin hasn't developed as yet.

Developing a Strain from a Single Fish

Photo: Two very young male Bronze Sailfin Mollies showing the improved coloration I selected for. They are too young to sport nice sailfins, but they grew up with large dorsals. As evidence of their youth, look at their gonopodia (anal fin), which are just beginning to develop.

How many times have you seen a single, unique fish and thought, “I’d like to have a true breeding strain that looks just like that fish?” Okay, I’m relatively sure most of you reading this haven’t thought that, but I’m writing this for the few fish nuts (although it’ll apply to anyone developing any animal or plant strain) who would think that. By the way, there isn’t a day that goes by when that thought doesn’t cross my mind. If Susie, my wife and very, very, very conservative business manager, would let me, I’d have dozens of greenhouses just to house the almost infinite number of fish strains I’d like to develop. In fact, my concept of Heaven is having unlimited resources to do so.

Anyway, surely some of you have been looking through fish at your local fish store, which is hopefully a mom & pop, independent retailer and not a big box store, and saw a unique fish you’d like to reproduce. (For my blog on the demise of mom & pop stores, see: and for a blog on a successful mom & pop store, see: Inevitably, that fish is a loner. It’s usually a spectacular male and there are no related females with him. Or, it’s beautiful fish in a tank of unremarkable relatives. Or, you ordered a fish online that arrives as advertised, but the females with him obviously are from some other strain. This latter occurrence is more common than you’d think.

So, what do you do? I’m going to use an actual example to illustrate what to do. I originally wrote about this subject for my column in the Tropical Fish Hobbyist (TFH) magazine. The article was titled “Bronze and Bronze Marble Sailfin Mollies,” but I was just using them as a How-To example. Here’s a link to the article:

I’ve read my contract with TFH and I’m not sure if the article is exclusively theirs, so in an abundance of caution, I’ll give them attribution and avoid plagiarizing myself. I’ll summarize the pertinent parts needed for this blog, but if you want to read the full, original column, please follow the link. TFH has been a longtime contributor to the aquarium hobby. As a child I avidly read the magazine, and anything written by its founder and aquarium hobby uber-promoter, Herbert Axelrod.

The pertinent information is that I bought from a retail store a male molly (hereinafter, the “purchased male”), the ancestor of our Bronze Sailfin and Bronze Marble Sailfin Molly strains. The females with the males were certainly unrelated, since they were albinos. I surmised the breeder didn’t want others to raise his/her fish and compete. Nevertheless, I thought I could recreate the strain, so I bought a “pair.” The albino female promptly died, but I had other females to mate with him.

Here’s a photo of a male molly that looks much like the purchased male; unfortunately, at the time I got him I didn’t have a digital camera. Taking non-digital photos and waiting to get them developed before seeing if they are any good clashes with my impatient nature. As a result, I took few photos back then. Contrast his photo with the photo at the top of this blog and you’ll see what careful selection can do.

Photo of an early breeder male Bronze Sailfin Molly

An early breeder male Bronze Sailfin Molly.

The next photo shows typical breeder females of the Bronze Sailfin strain. These, despite generations of inbreeding, are healthy, robust fish.

Photo of a good female Bronze Sailfin Molly.

A good female Bronze Sailfin Molly.

That background out of the way, let’s go into what I did. First, I mated the purchased male to some wild type molly females, Poecilia latipinna. Here are links to some blogs I’ve written about this species:

The purchased male was probably a hybrid of one or more of the various species of mollies, which are fish in the Poecilia genus. He was a sailfin molly since he sported a large dorsal fin. There are three species of sailfin mollies, the aforementioned P. latipinna, P. petenensis (also, erroneously known as P. kykesis), and P. velifera. It didn’t really matter to me since all mollies readily hybridize. I decided to use the female P. latipinna because I had them on hand, and they weren’t hybrids with all kinds of crazy gene combinations. Also, I wanted to use a sailfin molly to retain the nice dorsal of the purchased male.

First step was chunking the purchased male into a vat of P. latipinna females. I didn’t bother raising virgin females for this step. For those of you not familiar with breeding Poeciliidae fish (mollies, guppies, swordtails, plates, and their relatives), the females of this family of fish can store sperm. This means if you want to be sure a male is the father of a female’s fry, she can never have been exposed to another male. Guppy breeders, in particular, go to extreme lengths to produce virgin females. That’s much too much labor for me. And, I was pretty sure I’d be able to select fish that the purchased male sired by their appearance. For example, I expected his offspring to show some bronze color, a color P. latipinna doesn’t express. I was right, because the resulting male F1 fish showed some bronze even though the females looked very much like P. latipinna females, greenish-gray in color.

Since the purchased male lived long enough for his offspring to mature, I mated him to his daughters and then to his grand-daughters. By the time he died, some of his male offspring showed decent bronze color and nice sailfins. Even the female offspring displayed some bronze behind their gills. Basically, at this point, four generations counting the purchased male and his P. latipinna consorts, I had a strain of Bronze Sailfin Mollies. I set out to improve the strain by selecting the males and females with the best bronze coloration.

So, to recap, I’d acquired a single male from which I wanted to create strain; I hybridized to combine the bronze coloration with nice sailfins; and I used inbreeding to set the strain. The resulting fish were much nicer than the purchased male, with deeper bronze coloration, better color coverage, and a much-improved sailfin. Also, because I selected for size as well, the fish grew larger.

Similarly, I took a Bronze Sailfin male and gave him some Marble Sailfin Mollies and, using the same method, produced our Bronze Marble Sailfin Molly strain.

You should have noticed that inbreeding was used to set the strain. Here’s a quote about inbreeding from the TFH article, “A quick word about inbreeding. Inbreeding gets a lot of bad press, but it is the single most effective way to fix a strain. It’s used extensively in agriculture. Without it we wouldn’t have fantastically productive milk cows, chickens that lay an egg a day, fast horses…well, you get the point. You might have heard of the evils of inbreeding depression, the deterioration of a strain because of long term inbreeding. This is more a reflection on the abilities of the breeders (the people, not the fish) than inbreeding. We inbreed intensively. Our prize winning monstrous, vigorous mollies are the results of many generations of inbreeding combined with rigorous selection. As an example of inbreeding and how it doesn’t lead to deterioration, Texas State University’s Xiphophorus Genetic Stock Center has a line of Xiphophorus maculatus, the moon platy, originally collected by Dr. Myron Gordon. This line has been inbred by brother/sister matings for over 100 generations. The fish are robust, fertile, fecund, vigorous, non-deformed, etc. No inbreeding depression there.”

The method described above can be used to replicate any fish to create a strain (assuming the fish hasn’t been hormone treated or dyed or had some non-heritable condition). If the original fish doesn’t survive long enough to breed back to it (inbreeding), simply take its offspring and mate them together (also inbreeding). Keep selecting the fish that look most like the original fish and mate them together until you’ve yielded what you want.

A postscript:

We suffered some significant set backs due to Hurricane Harvey, whose eye passed over us. We had to operate on generator power for eight days and are still suffering repercussions of the storm. During the storm and its aftermath, we lost our breeding colonies of Bronze Sailfins and Bronze Marble Sailfins. Fortunately, we saved some youngsters and are in the midst of rebuilding our breeding colonies. It will, however, take some time to reproduce the best of these two strains.

If you are interested in our Hurricane Harvey travails, here is a link:

Good fishkeeping!