George T. Mormann

Tag: tropical fish

Unmasking the Marmorkreb


Among all the fish and invertebrates available to us in the hobby, few possess an origin story that is the stuff of urban legend. It was not under a rock in a stream, or a specimen scavenging the shallows of a murky lake where the marmorkreb was first found. It was “discovered” by a customer in a German pet shop, where it was labeled as a “Texas crayfish.” The date, much like the facts surrounding how it arrived in that pet shop, is disputed, but it’s said to have been the early nineties, shortly after the fall of the Berlin Wall.

The customer, believing it to be a simple crayfish from the Lonestar state, was astounded when he spotted several baby crayfish scurrying throughout the fishtank. He returned to the pet shop and asked how a lone crayfish could produce offspring without a mate. This is the first known observation of the marmorkreb, colloquially called the marbled crayfish or the self-cloning lobster.

Marbled crayfish were an instant sensation among hobbyists and scientists alike, becoming an ubiquitous addition to German aquariums throughout the nineties, and an enigma to scientists who spent years simply trying to determine their origin. In February of this year, The New York Times even published an article about marmorkrebs.

Initially, marmorkrebs were considered a close relative, even a mutation of the slough crayfish Procambarus fallax, native to Georgia and Florida. However, no crayfish matching the marmorkreb were ever found inhabiting North American waters. This led to it being the only decapod in the aquarium hobby besides daphnia to have it’s entire genome sequenced! In December 2017, the marmorkreb was finally designated as a species of its own: Procambarus virginalis.

The popularity of marmorkrebs, coupled with their unstoppable parthenogenesis, led to one of the most important rules in fishkeeping to be broken: don’t release your fish and invertebrates into the wild. Here is where another characteristic of this crayfish was realized the hard way — they adapt to virtually every freshwater environment they inhabit. Numerous countries throughout Europe list marmorkrebs as an invasive species, causing the European Union to enact an unconditional ban on owning or selling P. virginalis. The species has even invaded waters in Japan and Madagascar, where it’s feared to out-compete native crayfish populations. Though their true origin may never be known, it is agreed that whatever mutation had occurred, a truly invulnerable creature arose.

My own story with this aquatic anomaly began much like the informal discovery of them in Germany. At one of my local fish stores, I spotted several tiny, white crayfish labeled as “self-cloning lobsters” on sale, three for five dollars.

I quarantined them in a twenty gallon tank, and fed them sinking crab pellets and beef heart. The trio grew up together in relative harmony until they reached two inches in length, when they started to exhibit signs of sparring with each other. Each crayfish was moved to community aquariums, where I observed stunning differences in their personalities.

This is not a shy crayfish. Like some bottom-dwellers, I noticed that increased activity towards the middle and upper levels of my aquariums encouraged the marmorkrebs to come out of hiding, and remain out in the open even as I tended to the aquarium. Two of my marmorkrebs did not show predatory behavior towards fish, however, one would attack any fish that approached the bottom of the tank, going as far as chasing the fish in an attempt to grab it. Take care not to keep these crayfish with slow and tranquil fish, or bottom-dwellers like corydoras.

Marmorkrebs have voracious appetites, which is no surprise considering their nature as scavengers. I feed mine sinking pellets such as those one might find recommended for shrimp, crabs, or omnivores. They readily eat beef heart, blood worm, and in my humble opinion, are one of the most effective snail eaters next to assassin snails. I do not recommend any crayfish for planted tanks, but if you have pest snail problem, they will provide a solution. I often collect pest snails from aquariums and feed them to my crayfish as a part of their daily diet.

Conditions for keeping marmorkrebs are practically effortless. I maintain their temperature at 76 degrees Fahrenheit, but have kept them in a variety of temperatures from 68 up to 82 degrees. So long as room temperature falls within those parameters, a heater isn’t required. As with any aquarium, water quality ought to be clean and healthy as scavengers eat a lot and produce a lot of detritus. However, a simple bubble filter will suffice so long as water changes are consistent. They appreciate ample hiding spaces, especially when they’re molting or when multiple marmorkrebs are housed together. A single marmorkreb will thrive in a minimum tank size of 30″ x 12″ (20 gallon long).

As far as breeding marmorkrebs is concerned, it takes only one to tango. They produce clones of themselves through self-fertilization. I would advise removing the mother crayfish when hatchlings are found. Although the offspring are regarded as genetic reproductions of the mother, they will often develop unique colors that can change for a variety of instances. Mine generally develop marbled blue bodies, whereas other “kreb keepers” have noted instances of purple, red, green, and translucent or opaque carapaces.

Before acquiring this fascinating crayfish, it is imperative to make sure it is legal to keep P. virginalis in your state. Like the European Union, some states are proactively passing laws regarding the possession and release of invertebrates.

Overview: Procambarus virginalis

Maximum adult size: 4″-6″

Minimum tank size: 20 gallons

Temperature: 68-82 degrees

pH: 6.0-8.5

Diet: omnivorous







My Nano Aquarium


I’ve been a freshwater aquarist for over twenty years, but I usually avoid keeping any tanks smaller than ten gallons. Don’t get me wrong, I find the increasingly popular trend of nano fish-keeping a grand idea, especially admiring the designs of some of those nano setups. However, I like a tank that flourishes, and I don’t like stuffing fish inside the aquatic equivalent of a studio apartment.


Heterandria formosa

Well, a couple of weeks ago, I attended a meeting at my local fish club. The meeting always closes with a mini-auction, where I usually stock up on hornwort, guppy grass, and occasionally, fish that I would like to keep. I won a couple of breeding pairs of Least killifish (Heterandria formosa). Not a true killifish, but a livebearer closely related to guppies and mollies, of the family Poeciliidae. They are one of the smallest livebearers in the world, and considered the smallest among North American livebearing fishes, being endemic to Florida. With the females barely exceeding an inch and a half, I didn’t feel comfortable adding these fish to an established aquarium, where they might be out-competed for food, or worse, become food. A year ago, I bought a Fluval Spec V for less than half it’s retail value, but had yet to use it for the reasons specified above. So I decided to set up the Spec V as a single species starter colony for these shy yet fascinating fish! The plants are hornwort (yes, I have to trim it weekly for it grows like a weed) and staurogyne repens. The substrate is Eco-Complete, and within the filter reservoir is a 25 watt, pre-set heater, which maintains a temperature of about 76 degrees Fahrenheit.


The Best Instagram in Town

Lately, I’ve been dedicating more time to my aquarium hobby than writing content for my website. I’ve been a freshwater aquarist for over twenty years, and these past two years I have really invested a great deal towards raising and breeding various fish, invertebrates, and growing aquatic plants and mosses. As I establish and decorate more aquariums, I wanted to start an Instagram page focused on my variety of fish tanks. My Instagram photos can be found at the bottom of this website. Please have a look at my photos and feel free to like and comment. Regardless of whether you’re a fellow fishkeeper or an admirer of the hobby, I enjoy talking about aquariums.

My Instagram

So as to Mimic Their Natural Environment


The Author’s 10 Gallon Betta Riverbed

I take solace in
for my pet fish.
This is my sole
purview, no less
relentless than
destiny, or
one’s career.

I research their
native ponds, read
the curvature
of every
twig so I may
learn how to reach
beneath currents
and transfer my
solace unto
my pet fish.

I google how
stones lay themselves
on the river
floor, seamlessly
bound to the next
like a necklace
carelessly, yet
tossed away by
a whimsical,
but scorned woman.

If only I
could ask her how,
how to place each
rock so they might
spawn a blanket
of moss because
I will forget
to feed my fish
on some days.