Livebearers Unlimited: The Fancy Molly: The Most Spectacular Freshwater Fish You've Never Seen

Author: Ted Coletti, PhD

What is the most spectacular freshwater fish parading through your pet shop? We all have our preferences. (Yes Wayne, we know, “Geophagus cichlids.” Now go back and play with your tarzoos). But what I’m talking about here is the “wow” factor—the fish that makes your jaw drop and heart beat. Relegating this exercise to only the hundreds of common fish seen throughout the year, I would argue that it is a male fancy sailfin molly.

And in my 24 years in this hobby, I’ve rarely seen one in a pet shop.

Proper Care

Oh, I’ve seen fancy sailfin mollies, mind you. Lots. And they are nearly always lethargic, clamped, fungused, overcrowded, or displaying the “shimmy dance” of which they are infamous. As most hobbyists are not properly instructed on their care, buying these already-compromised fish should really be accompanied by a loud cry of “dead fish walkin!” by the store staff.

On the other hand, if you have ever maintained a pair or two of fancy sailfin mollies successfully and properly in your home aquarium, you have been treated to a sight that you will never, ever forget in your hobby lifetime. A giant sailfin dorsal standing erect by a male fluttering and circling about the female, his colors intensifying as his scales protrude ever so slightly. And he does this continually throughout the day. The females flutter as well when interested, and cultivated females are almost as colorful as the males. Mating is a cooperative effort, a spectacular site to behold indeed!

And therein, dear hobbyist, lies the rub. A beauty concealed by sickliness. Don’t blame your dealers—they are as frustrated as you are. You can apply this same dilemma to the black molly (see my TFH September 2006 column on the origin of this particular fish), and to other short-finned fancy mollies to a lesser extent.

Tough Love

Yes, mollies are frustrating beauties indeed! The conventional wisdom still touted in books, the Internet, and Q&A columns is that all this poor health is because mollies are brackish-water fish. In the pet shops and home aquariums where they are deposited, they are simply not being given their indigenous water chemistry. Wrong.

I feel every hobbyist should attempt a healthy fancy molly tank at least once in their lifetime. So let’s review the facts, fiction, and format for fancy mollies. This month we’re going to try to understand what exactly a molly is, and the differences between the species. This provides a good basis for understanding what to expect when you purchase either a wild-type or cultivated variety.

In my opinion, mollies have never been adequately or accurately reviewed in the aquarium literature. They have fascinated scientists for decades because of their diversity of habitat, body size, male secondary sex characters, and mating behaviors (Ptacek, 2005). And new findings from the ichthyologic community are shedding light on the evolution of this fascinating group of livebearers.

What is a Molly, Anyway?

“Mollies” is the common name for a subset of livebearing freshwater fish from the genus Poecilia, family Poecilidae. Poecilia includes several sub-genera (today more commonly referred to as “clades”), some of which seem to be moving toward independent genus status.

This curious lumping of so many distinct fish from guppies to mollies into one genus is because of the historic Rosen and Bailey re-classification nearly 50 years ago. This occurred right before the dawn of the modern cladistics age of taxonomy, which uses computer-driven statistical “cluster analysis” to sort through reams of data to find relationships between fishes. Rosen and Bailey also didn’t have modern DNA sequencing technology to aid them. These two advancements in taxonomy resulted in the “splitting” movement that the cichlid hobby has been going through (or suffering through) for the past couple of decades.

Limias, which are sometimes called the Caribbean mollies and share many behavioral and morphological traits, have already been split out from Poecilia to their own genus. The rest of Poecilia is long overdue for a splitting in my opinion. Poecilia clades include Lebistes, which contains the ever-popular guppy, Endler’s livebearer, and a few other related animals like Micropoecilia (sometimes referenced as its own genus). There is also Pamphorichthys, a South American group not widely kept in aquariums.

The Genus Poecilia

What, then, in the genus Poecilia is considered a molly? Essentially everything else. The late great Robert Rush Miller established the Mollienesia clade in 1975, resurrecting their old genus name from days of yore. Visually, male mollies tend to be more deeper-bodied than other Poecilia. The contrast with guppies and related fish is obvious. Males also tend to display their dorsal fin, which has comparatively more rays.

To make things more complicated, within Mollienesia there are two complexes. Males from these two complexes differ in both morphology and behavior. And they cover habitats ranging from inland mud swamps to coastal lagoons. This makes it erroneous, in my opinion, to make any generalizations about the “natural habitat” or “water conditions” of any pet-shop or fancy molly; pet-shop or fancy mollies have been extensively hybridized over the past 80 years!

The latipinna Complex (Sail-Finned)

The latipinna complex of the Mollienesia clade houses the sailfin mollies P. latipinna (native to the United States and Mexico), P. velifera from the Yucatan, and P. kykesis from Guatemala, Belize, and Mexico. These three species (first latipinna, then velifera, then kykesis) have been hybridized to form the basis for the fancy sailfin and black mollies we enjoy (or try to enjoy) today. All three species have unique color and finnage attributes, but of the three, P. velifera is the largest in body and dorsal fin. It also has the most elaborate courtship display, swimming in circles around the female as it displays its huge dorsal fin. This is a must-have livebearer, folks! Geographic variants with different colors are common, indicating a good degree of polymorphism, and thus creating the basis for the myriad of color varieties we enjoy today.

Margaret Ptacek (2005) maintains that the evolution of the spectacular finnage and dramatic male courtship displays in the latipinna complex is due to pre-existing female sensory preference for such traits. It also has resulted in females preferring males of their own species—and even their own populations—which has prevented runaway natural hybridization with so many molly species living side by side in nature. This is a similar theory used to explain the greatly exaggerated caudal fin in the Montezuma swordtail Xiphophorus montezumae (see my TFH April and May 2005 columns). And this finnage is still evolving!

Sailfin males also tend to be larger bodied, and they need female cooperation for mating (like the goodeids), thus the reason for elaborate courtship displays. I have found this to be even more pervasive in the wild-type species, which have not been “diluted” by short-fin molly genetics.

Latipinna complexmolliesare also euryhaline species; they can adapt to a wide range of salinities. Note the word here is “adapt” not “demand.” The members of this complex also have wide, upturned mouths that enable them to exploit the thin film of oxygen-rich surface water when living in depleted waters. With their love for algae (they are still omnivores, contrary to popular belief), sailfin mollies make great summer tub and pond fish.

The sphenops Complex (Short-Finned)

The short-finned Molliensia are called the sphenops complex. This is comprised by at least P. mexicana, P. gillii, P. butleri, P. marcellinoi, and P. sphenops (Poeser, 2005), extending to P. catemaconis, P. chica, P. pallida (maylandi), P. orri, P. sulphuraria, P. tereseae (Ptacek & Breden, 1998),and the new P. rositae. The South American mollies are P. vivipara and P. caucana. The latter has been making the rounds in the organized hobby and auction sites in the past couple of years. (David Lains and I worry these might be a misidentified liberty-type molly, or a hybrid.)

Unlike the sailfins, males from the sphenops complex are best characterized as “thrusters,” and thus are generally smaller than their female counterparts. But that doesn’t mean that short-finned mollies are without appeal for the home aquarium. Behaviorally they present a dominance hierarchy with alpha males and male trait suppression in subordinate males. Limias show a near-identical social structure, and indeed are very closely related to mollies. Many short-finned mollies have been used to invigorate and further hybridize fancy molly strains over the years.

There are also the famed liberty mollies with their variegated dorsals, which were broken out to a P. salvatoris complex by Stanley Weitzman of the Smithsonian a few years back and presented here in the pages of TFH. There are also three species Dr. Fred Poser (2005) believes to have evolved as natural hybrids between a sailfin and short-finned molly: P. formosa, P. petenensis, and P. latipunctata. This latter species is short-finned but retains the dramatic courtship display behavior that is a hallmark of the latipinna complex.

That leaves us with almost 20 recognized molly species and growing, not to mention numerous morphologically distinct races. Phew! Enough of the taxonomy deep-dive, I’m starting to sound like Wayne Leibel now, and I haven’t even written four columns on the subject yet! The important thing to remember here is that the fancy mollies you get at the shops and see in pictures are all hybrids of various species. You would think that this should make them hardier through hybrid vigor, but it hasn’t.

We’ll discuss this paradox next time, along with how to care for these big, beautiful fish. Along the way we’ll shatter a few myths and probably be obnoxious to more of my fellow columnists. Stay tuned!