Photo of a male Giant Marble Liberty Molly

Giant Marble Liberty Molly Update

Photo: Our current Giant Marble Liberty Molly breeder male.

I originally wrote about this fish in May, 2015 (see my blog We have now gone through a couple of additional generations so I’m providing an update on the status of this molly strain. Please read the earlier blog for its history.

I plan to use this strain to demonstrate two breeding techniques, out-crossing (hybridizing) and inbreeding.

Out-crossing took place in 2013 when I set up the mating of Poecilia mexicana, Campeche males with P. velifera, Campeche females. Why this particular cross? I had long wanted to combine the bluish body color of P. mexicana with spectacular dorsal and large body size of P. velifera, which is the largest of the three wild sailfin molly species.

As I wrote in the earlier blog, I didn’t expect much from this cross because earlier matings between P. mexicana and P. velifera hadn’t produced anything spectacular, but I’d never used these collections of the two species. Both were from Campeche, Mexico and both were nicer than many other populations of the two species. This particular cross produced very nice F1s (first generation hybrids). The males had powder blue bodies and were large, much closer in size to P. velifera than P. mexicana. There were non-marbled fish and marbled fish. None had sailfins. They reminded me of large old-style liberty mollies, hence the new name I gave them: Giant Liberty Molly. I called the marbled fish Giant Marble Liberty Mollies. As you can tell, I’m very creative with naming.

It’s worth noting that when hybridizing using two species (inter-specific hybridization) the first generation (F1) offspring are very uniform. It’s in subsequent generations that lots of variety appears as the parental genes are recombined and mixed. In the F1 generation all fish have half their genes from one parent species and the other half from the other parent. In later generations these genes are mixed in different ratios.

In the next step, inbreeding, I selected the three best males and 10 females as breeders. The next generation I selected three very large, nice males and 22 large females. This last generation I have intensified inbreeding by selecting only one male (very large) and eight very large females as breeders. Their offspring will be a mixture of full and half siblings.

While the selected male doesn’t show as much blue color in the body as I like, he is nicely marbled and is very large, over four inches in total length. The eight females are even larger and show nice marbling. I have over 150 juveniles and young adults growing up, some of which might be future breeders. The marbling isn’t set in this strain so it also yielded nice fish that weren’t marbled; in fact, about another 150 fish. These were moved to our Giant Liberty Molly grow-out vats for future consideration as breeders in that strain. The photo  below shows a couple of young adults that show promise, assuming they grow large enough.

Photo of Two young adult Giant Marble Liberty Mollies.

Two young adult Giant Marble Liberty Mollies.

This process of hybridization followed by inbreeding is something I replicate often in developing commercial fish strains. I look at two varieties and see characteristics I wish to combine. First, I breed the two varieties together to yield hybrids; this is out-crossing or hybridizing. In this particular case I was originally hoping to combine the blue body color from P. mexicana with the large dorsal and body size from P. velifera. As often happens, the cross yielded something unexpected, a large marbled liberty molly looking fish (as well as the large non-marble liberty molly looking fish). Once I saw them I wanted to improve and set the strain and embarked on inbreeding.

In inbreeding programs it is important to produce large numbers of offspring since often what you want requires a combination of genes that might be rare. That’s why I used multiple males and females. Fortunately I had several good prospects of both sexes so could set up a relatively large breeding colony. Sometimes you have only a very few good fish and don’t have that luxury. Once I’m sure I can replicate the original fish, which happened in this strain, I get more selective about the breeders. In fact, the colony I set up has only the largest male and largest females. I hope to set the size first and then I’ll work on color, although I’m fairly satisfied with color and conformation of the present nine breeders.

As is typical of commercial molly strains not all offspring will fit the strain’s description and will be discarded. Fortunately for us we can sell these “culls” as mixed mollies and recoup the food they ate and the space they took up. It’s also from such “culls” that new potential strains can arise. I’ll consider the stain set when 95% of each generation is marbled and large.

This strain is lucky in a way. Susie, my wife and business partner, demands that my “experimental” fish strains are eventually (actually sooner than that) commercially useful. Susie happens to like this strain (read: they can be sold for a profit) and looks forward to when I’m comfortable with releasing them for sale. That should happen soon and I’ll start producing a hundred to two hundred fish a month.

To recap, hybridize to combine characteristics from two different strains and inbreed to set the desired combination.

Good fishkeeping!