By Ivan Mikolji / 2014
I turn my head left and see hundreds of cardinal tetras shoaling on the river bank. Small sections of my ears are raw due to many tetras, Copella and Anostomus that are constantly biting and nibbling on them. Even though their teeth are small, the mass number of them do damage to your skin, after days of snorkeling in their habitat. Scouting the area, I spot a good-looking, medium sized peacock bass swimming towards me. He is far enough to let me prepare for a possible amazing picture. I hyperventilate a bit and take a deep long breath. As I sink towards the river bottom, I relax my muscles and try to concentrate by ignoring the painful “skin peeling” going on in my ears. I do a smooth landing on the river bed with minimum debris stir. The Cichla still unaware of my presence gets closer as I lay motionless, five feet underwater. I try to anticipate its trajectory, fine tune the camera settings, and start to locate him on my cameras back screen. Twenty seconds have passed; I can hold my breath for about a minute so everything is looking o.k. as long as the bass does not stop for a rest along the way. All of a sudden a brown “thing” comes up the front of my mask. It rises and parks itself so close to my left eye mask glass that I cannot even focus. By experience, I know what it is and try to ignore that, too. The Cichla keeps on swimming until he is two feet away and then spots me. In the fraction of a second in which the fish is thinking what to do is when I snap the picture. I head up to the surface to get some air and the brown thing is still stuck to my mask glass. Once I’m able to fill my lungs back with air, I smile. I know that the brown thing is a Monocirrhus polyacanthus that has come to try to capture some of the fish that are chomping on my ears but to me, he is an old friend that has come to say, “Welcome to the Amazon!”
I don’t understand why I can see cardinal tetras, flag cichlids, and so many other fish species underwater in the wild but only Monocirrhus polyacanthus makes me really feel that Amazon spirit. This is a special fish that to me contains the jungle essence in its DNA. My words to describe it would be secluded, strange, rare, magical, cool, mysterious, all which describe a superb tropical fish for an Amazon aquarium enthusiast.
M. polyacanthus is a widespread species present in many South American countries from Bolivia up to the Orinoco River, in southern Venezuela. Due to its vast geographical presence, it for sure inhabits many different types of aquatic biotopes. I will describe the small, clear water habitats that I have seen them in and that can be reproduced or imitated by us, at home. The clear Amazon streams information that I will give you is not conclusive, for example, I have never seen floating aquatic plants in their habitat but that does not mean that they are not present in other locations. Habitats also change with the seasons which add diversity and fun challenges to any serious aquarist. I will use M. polyacanthus physical characteristics, behavior and habitat observations, blend the information to give you the Mikolji point of view of what a leaf fish aquarium should contain. So, to recreate the M. polyacanthus biotope, we need its original water parameters which are pH: under 5, KH: less than 20mg/L (ppm), GH: less than 10mg/L (ppm), Temp: 26 ° to 29 ° Celsius. The sections of the stream where M. polyacanthus are found are slow moving Amazon lotic ecosystems so try to keep water movement to a minimum and defuse filtration output streams. The substrate as a base should consist of white silica sand of an approximate 16/30 mesh. I personally love this sand as it is the one found in the wild and it is usually chemically inert, and consequently, will not alter your water parameters.
M. polyacanthus have developed characteristics that enable them to mimic fallen dead leaves from the riparian vegetation, characterized by hydrophilic plants. They use dead leaves crypsis both for defense and for hunting their prey. They glide over the decaying leaf litter unobtrusively by gently moving their little transparent fins. It is incredible how they seem to fly or drift from one place to another with no apparent movements of their fins. The silica sand bottom should be topped with leaf litter. The size of the leaves should not exceed double the length of your M. polyacanthus and they should be in the ochre color range, not green. It is hard to find a green fallen tree leaf underwater in their habitat. M. polyacanthus are like a water chameleon. I have seen them in black, brown, brick red, orange, and sometimes, bright yellow!
Throughout the years of field observation, I have seen M. polyacanthus strictly residing on the river bed and occasionally right beneath the water surface. They are not mid water dwellers at all and actually seem to be benthic. When seen on the surface they take refuge under leaves that are half submerged in the water. These half submerged leaves probably not only serve them as refuge but also to lay their eggs. They cross the rivers in 2 altitudes and different cruising speeds. When they cross a stream at river surface cruising altitude, they are relatively fast to get to the other side. Never showing erratic movements, they seem to flow with the current even if they are going against the current. When they glide at ground level they do it slower as if they were scanning the area for prey or predators. In order to recreate the near surface area of the biotope, I would suggest any plant (Philodendron species) that can be kept in pots outside or with their roots in the same tankwater, allowing the leaves to dip into the aquarium.
Our main character, Mr. Leaf Fish, is an outrageous predator that swallows its prey whole. Because it is a slow swimming, slow moving fish, it relies on its mimicking shape, swimming position, and camouflage to ambush its prey. Once in range of a succulent, unfortunate, unaware critter, it uses its protruding jaw to suck and trap its prey in its mouth cavity. The victim will never know what happened! The protruded jaw is hard to see when it strikes a victim because it is extremely fast but he will also show it off regularly as this fish loves to “yawn” many times a day. The fish that live their lives near him but unaware of his existence include small sized Hyphessobrycon, Pristella and small tetras such as Paracheirodon axelrodi. Some larger species like Satanoperca daemon are always bothering him as they move the leaves around to reach and sift the silica sand substrate below.
The way it is usually found swimming vertically with its mouth down makes me wonder if benthic prey are easier for him to capture compared to pelagic swimmers, such as cardinal tetras. If you think about it, bottom dwelling critters cannot swim downward to escape. With this concept in mind, we can plan the tank mates that can co-exist or feed Mr. Leaf Fish. I would add any inexpensive small freshwater shrimps, such as ghost shrimps. These crustaceans will keep the leaf litter clean and will be his prime food source. If you add small fish you have to be aware and ok with them being eaten by Mr. Leaf Fish, so you might want to keep cheap tetras, if they are small enough to be swallowed. If you want to keep fish out of his diet, buy any species of tetra that will not fit in its mouth. I would suggest leaving the middle of the aquarium bare to keep larger schooling tetras, such as Hyphessobrycon that are big enough not to be swallowed him but small enough not to be able to eat the shrimp.
In the breeding season, M. polyacanthus preys on fry from Apistogramma, Crenicihla or any other species which as adults are too big for him to swallow. Leaf fish prey on many fish that have not had the chance to mature and be able to reproduce. Small crustaceans also become the leaf fish victims but contrary to what most people think, freshwater invertebrates, including shrimps are not extremely abundant in the Amazon streams. However, they are present in the leaf litter and make part of its raw bar menu. The impact of M. polyacanthus in the Amazon streams trophic cascade is quite uncertain to me but for sure they are a key species which keeps overpopulation of small fauna under control.
Strong light rarely penetrates the leaf fish habitat, when direct light does penetrate, it does it in rays that trickle in between slight openings in the tree canopy above. Light rays can probably be simulated by placing a piece of cardboard, wood, or dark plastic with a few small holes between the top lights of the aquarium and the water surface. Do not overdo the light, it is not needed, use as much needed to be able to see the fish. A great example of illumination would be a very romantic candle light dinner. Keep water currents or movement to a minimum. Do not place green leaves in the bottom of the aquarium, trust me, he will not turn green!
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