By Ivan Mikolji / 2015
I wish I was able to breath underwater. I wish I could stay here in the Green Tunnel; make time freeze. This is natural perfection. The Green Tunnel stretches as far as I can see in the underwater horizon. Brycons, Moenkhausia, and other pelagic tetras swim past me and disappear in the distance as they go somewhere. Some come with the flow and some swim against it, up river. The long aquatic plant leaves sway from side to side with the strong water current. Everything is so green. As I hug the fallen tree trunk with my legs, I sit there and take the time to admire the underwater movements. My favorite are the incredible underwater reflections. They are not tangible but you can see them, they are optical illusions that multiply the natural beauty by two.
A Green Tunnel is a narrow canal that connects two tropical rainforest stream pools. Technically speaking they could be categorized as “runs.” As a stream narrows, the water picks up speed. I was already cold in the pool downstream, here I’m shivering. The water current creates a “watershield” effect that makes me shake uncontrollably. The shakes come every 30 to 40 seconds and they last about 10 seconds. If I concentrate really well and relax my muscles, I can sometimes stop the shivers a second after they start. I have my usual gear on, my wetsuit, 14 kilogram lead belt, video camera, and photo camera.
So my legs are still hugging the fallen tree trunk. I feel like I am riding an underwater motorcycle. If I let my legs go, the water just drags me down river at quite a fast pace. I wedge the video camera into the soft river bottom, hug my photo camera, take a deep breath and lie down backwards until my back is on the tree trunk. Now, I’m lying down in heaven. This is a total different perspective, maybe what you would see, if you could lie down, inside your aquarium. As I lie there, I spot one of the few unusual fish that make the Green Tunnel their home, the Green Dartfish, Ammocryptocharax elegans.
In a fraction of a second, my mind switches from dreamland mode to work mode. I am on the Green Dartfish. My eyes do not get off it for more than a second at a time. The fish is as green as the swaying aquatic plants and only about 4cm/1.57in long. This is a fish that resembles a Green Iguana in color and how it moves over the underwater elements. It actually crawls on the aquatic plants using its pectoral fins. Even though the water current is extremely fast, the Green Dartfish manages to make it look as if there was none. You can tell they have completely adapted to this habitat. They are slender, tube-like with a pointed face. Their large pectoral fins are extremely interesting and used just like wings on an airplane. The front part of the pectoral fin helps them crawl and anchor to the substrate. This is a key function as it keeps them close to their food source, lets them save energy by not having to swim constantly and helps them stay camouflaged from possible predators. The back part of the pectoral fins move up and down just like ailerons to keep on the ground or lifting off to the next spot. Sometimes, they stop in mid water and seem not to move any fins. Upon closer observations, I noticed the pectoral fins adopt a ∾ shape probably acting as flaps increasing the drag and making them float statically and effortlessly in a strong current. Of course, now I feel a bit heartbroken; I am still hugging the tree trunk with my legs and shivering. My aquatic soul comes to the realization that even if I really want to be aquatic, I am not.
The Green Dartfish habitat is quite “clean” due to the strong current. Loose particles get dragged at high speed down river. Everything that floats downstream immediately gets inspected by the hungry tetras. If the gunk is edible, it gets swallowed, if not, it gets spit out. Inedible particles will get inspected by every tetra in the green tunnel until it slows down and precipitates to the pool bottom downstream. The only “dirty” looking thing here is the periphyton, but in the green tunnel, everything has to be anchored. Periphyton will only “flourish” on rough surfaces such as the tree trunk I am holding on to, small branches, Moriche Palm (Mauritia flexuosa) roots, and the serrated edges of some of the aquatic plants’ leaves.
So, our green friend crawls twice and then takes a bite of the gunk or periphyton that is stuck to all the rugged natural decor. It then stays put for half a minute or so and takes two crawls more. It then picks on the gunk again. This same behavior is seen if it is lying still on a stick or swaying in the long aquatic plants. Once you stare at the Green Dartfish for a while, you all of a sudden start seeing many others. In the two hours or so that I was in the green tunnel I spotted about ten of them. One of the curious freshwater, underwater, aquatic field observations was to see them very attracted to eating decomposing broken plant extremities. Wherever an aquatic plant stem or leaf breaks, the remaining stub tip starts decaying and usually turns into a white mush. A. elegans love to eat this stuff or whatever lives in the stuff (bacteria?). They seem particularly drawn to the decaying matter of Moucou moucous (Montrichardia arborescens) and Amazon Calla Lily (Urospatha sagittifolia) plants. They can spend a great deal of time picking at the whitish rotting stems. It did not occur to me to taste the slimy ultra-wilted salad, but they seemed to love it a lot.
It is curious that another of the permanent residents of these green tunnels are green, as well. I found Green Twig Catfish (Acestridium dichromum) living sympatrically with our Green Dart Fish. Although they seem to live in the same place and feed on the same stuff they do not compete or fight territorially. They are both extremely docile fish and after all, competition is low. There is not a line of fish beating themselves up to eat that gunk.
Water parameters are the same as in most of the Venezuelan, Amazonas, Orinoco River Basin streams. Low pH between 5.8 and 5.2 depending on the season. Temperature fluctuates between 23 and 26 Celsius. Small non-migratory fish such as the Green Dart Fish and Green Twig Catfish are present in this stream because it does not dry up in the dry season. If it did dry up, these species would not survive and the stream would be filled with larger pelagic or migratory fish. The bottom of the green tunnel is made out of hollow layers of decomposing materials. I tried to stand up, sank to my hips and did not hit bottom. I just felt cracking sticks and air bubbles coming out of the floor as I sank in it quicker than in quicksand. There is really no mud, sand, or floor, it is just like an endless sandwich of leaves and sticks. I held on to the tree trunk to avoid being swallowed by the “quick floor.” What lives down there? Who knows!
As usual, I make a plan, a photo strategy to get the best possible photographs. Taking images of fish in their natural habitat has many challenges. This particular green tunnel, has a heavily vegetated riparian zone. The thick foliage consisting of high Moriche Palms and tall trees make the whole scenery quite dark. Light rays penetrate the water as they trickle through the canopy high above. Light is almost absent at the base of the aquatic plants. As the sun shifts, so does the angle at which the light penetrates the biotope. Sometimes only one side of the biotope is lit up. As the trees above sway in the wind, the light rays become alive. It all resembles a natural discotheque with ecofriendly decor and an elaborate natural light show. As I do not use a flash, I had to follow and wait until our fish passed by one of the sun lit areas. Sometimes if there is turbulence on the water surface, such as, a small ripple or wave you could get an underwater spectrum. In these special circumstances if the angle is correct, light is broken by water just like a prism would. Seeing an underwater spectrum live in situ illuminating a Green Dart Fish in a green tunnel underwater garden, holding yourself to a fallen tree trunk with your legs, as you shiver uncontrollably and catching the image is something that will make me smile for the rest of my life.
This article has been published at:
• Practical Fishkeeping Magazine - May 2015
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