South American Leaffish, Monocrrhus polyacathus Heckel

An Unusual Predator, the Leaf Fish has Hidden Habits and History

Leaf Fish a South American Preditor Fish
Thomas R. Reich PhD

Range: Amazon and Reo Negro Basins; British Guiana.


Size:  3 inches, breeds at 2 inches


Temperament:  A predaceous species that will eat anything that it can get into its large mouth


Temperature Requirements:  73 – 90 F


Sex Differences:  Male has slightly larger fins


Breeding Habits:  It is not so much providing special conditions, as it is the luck of finding a pair that happens to be ready to breed.

  If they are ready to breed and there is a broad leaf plant such as an Amazon sword plant, they will lay eggs on the underside of the leaf.  The eggs will be tended to closely by both parents and hatch in 3-5 days.

The parents are attentive and protective of the fry for several weeks, the fry are transparent for about 2 weeks and will graze on infusoria that exists on mature plants and rocks in the aquarium.  After 2 weeks the fry should be removed and separated since they grow at different speeds, and larger fry will eat smaller fry as soon as they can fit the smaller fry in their mouths!

The fry must be fed ample supply of daphnia, mosquito larva and if available, guppy fry for fastest growth.  The fry are covered with white specks up until about 2 months of age, it looks like they have Ich, but this is just natural coloring for fry of this age.  After 2-3 months the fry will color up and be ready to eat larger fish, at this point they must be separated further.


Drawbacks:  The South American Leaffish or “Leaf Fish” gets its name because it looks like a dead leaf, remarkably like an actual dead leaf.  It looks this way because it is an ambush predator, laying in wait of any prey it can fit in its deceivingly large mouth, and its mouth opens much wider than it seems at first glance!

  This fish can eat its weight in live fish every day.  Even though it is only about 3 inches full grown, it can clean out your community aquarium in a week, and you will never know what happened.  Do not get one of these fish for a community aquarium!  In order for this fish to be kept alive, each fish must be fed at least 3 grown guppies per day, or they will quickly weaken and die.  How is that for a drawback!


The Story of the Amazon Leaf Fish

The Leaf Fish of the Amazon and the Guiana’s is a superb camouflage artist.  With colors varying from dark brown to gray, it drifts aimlessly through the water looking remarkably like one of a million real leaves in the stream.  So good is its camouflage that even in a net with assorted dead leaves and twigs, it is likely to be returned to the water unseen – unless it moves.

Dark coloring is only one in a whole bagful of camouflage tricks of the leaf fish.  The body, with its margin of jagged fins, is a perfect leaf outline.  From the eye radiate several dark lines resembling the veins of the leaf.  Many leaf fish have a quarter-inch-long flap of skin protruding from their lower lip that looks much like the stem of a leaf. 

To complete the deception, the only fins that normally move, the pectorals and the rear tips of the dorsal and anal fins, are transparent, nearly invisible when in motion.

  Further, leaf fish frequently swim at an unfishlike head-down angle.

While this clever camouflage gives the three-inch leaf fish wonderful protection from larger predatory fish, the main value of the camouflage is as an aid in capturing smaller fish.  The leaf fish may drift with the current until an unsuspecting smaller fish swims near, or it may sidle ever so slowly up to a fish until its mouth is almost touching.

Then, in a lightning-fast motion, the lower jaw swings down, and an unbelievably huge tube-like mouth unfolds and swings out, creating a suction that draws the unsuspecting victim in.  With a gulp, the hapless fish is gone.  Fully extended, the mouth is as long as the fish’s head.  Occasionally, the Leaf Fish extends its cavernous mouth for no apparent reason, as if it were yawning out of boredom.

Leaf Fish are good parents.  Eggs are usually deposited on the underside of a living leaf or on a stone, After the fish give much affectionate attention to each other, the female carefully deposits her eggs and the male fertilizes them.  Each egg is attached to the leaf or stone by a short thread.  Hence, the large glassy eggs are all raised slightly off the spawning site.

The male leaf fish stays close to the eggs, carefully fanning water over the eggs.  They hatch in about two or three days, but the babies remain attached to the spawning site by the egg thread for another week.  Once they are free-swimming, baby leaf fish act much like their parents, remaining still most of the time.  At first, young leaf fish eat small aquatic animals, but by the time they have grown to a half inch, they are able to eat small fish the size of baby guppies.

Leaf Fish do well in an aquarium, but they prefer to eat live fish as their main diet.  Guppies are eagerly eaten, but this can be costly food.  In some places, like the southern states, there is an abundance of small native fish that can be caught and fed to the Leaf Fish, see Mosquito Fish.


Note:  This is a very interesting fish for the classroom or for the collector with many aquariums that wants a conversation piece.  Remember, do not purchase and bring a fish home that you do not fully intend to take care of for a long time.  This is not a “novelty” that you feed guppies for a few weeks, get tired of the expense and let die.  It becomes your pet, a life you are responsible for.  If you commit to owning one of these remarkable and rare fish, understand the commitment you are making and fully embrace the challenge of a truly unusual fish.


For more information check out our Twitter, Facebook and Pinterest and feel free to ask questions by clicking here.  If you encounter problems, come back to and I will do my best to help your aquarium thrive.  I love fish and I want you to grow with the hobby.  I want you to have all the information at your fingertips to create a happy healthy aquarium community for you and your family.