Exploring the Rio Atabapo; The search for true Altum Angels

Chris Englezou Biotope, Biotopes of South America, Chris Englezou 7 Comments

In September 2014, I had the opportunity to travel along the border of Colombia and Venezuela and deep into the Venezuelan rainforest in search of the elusive Altum Angel of the Rio Atabapo and many other amazing species. Here is an account of my journey which was published in the April 2015 edition of Practical Fishkeeping Magazine. Enjoy, Chris.

As I stare out of the adjacent window eight thousand feet above land aboard this world war 2 DC3 cargo plane, the only flight going to our location, I am suddenly enamoured by this irreplicable view of untouched rainforest stretching right into the horizon in every direction; quite literally, there are millions of trees and it is absolutely amazing. Below me I see the meandering rivers and their associated lakes artistically displaying their history printed into the surrounding forest, never would I expect to have this captivating close aerial view of the rainforest, it certainly beats any commercial flight.   After 4 hours we arrive at Inirida, a town in the Colombian Amazon where we stay overnight; we begin our expedition very early the next morning, setting off from the docks onto the Inirida River we briefly travel along the Rio Guaviare, the last white water river we will see on this journey. Once we reach San Fernando, the junction where the Guaviare, Atabapo & Orinoco rivers all merge, we encounter a meeting of the water systems, the incredibly black waters of the Atabapo lay parallel to the silt-laden white waters of the Guaviare forming an undulating line as if two pieces of a puzzle, it’s not until many kilometres downriver into the combined ‘Orinoco’ where they begin to mix. It is an inspiring sight and evokes a real understanding of the vastness and diversity of these water systems. After half a day along the tea-coloured Atabapo, our first stop is ‘Merei’; it is a village of thirty nine families of native Kurripako descent. Jesus and Cristian, our boat guides have family here and we are permitted to look for fish by the head of the village. The water parameters are typical of this extreme black water river, a very acidic pH of 3.7, low conductivity of only 13μS and temperature at 28.6°C. In the shallows of our first biotope we find juvenile Twig Catfish, possibly Acestridium discus, perfectly imitating the grass-like blades of the submerged Bulbostylis cf. schomburgkiana (commonly mistaken for Cyperus sp.) lining the shore. Other intriguing species we find are the characoid, Crenuchus spilurus, Iguanodectes cf geisleri, the beautifully spotted Copella cf meinkeni, juvenile Metynnis hypsauchen with an iridescent golden operculum and suborbital region and some young predators, Hoplias and Erythrinus. Into my netting I catch a young Mesonauta egrigius, a species which is endemic to the Orinoco drainage; its gold base colour is breathtaking and I find myself uttering the phrase, “there must be something in the water”; many species show especially golden colouring in this and other extreme blackwater biotopes compared to other regional variants and related species.

Close by at the waters edge, we find some large shoals of Hemiodus gracilis numbering several hundred per shoal and watch them whizzing along the shallows around the granite boulders. In amongst the group are Hemiodus cf. thayeri living in mimicry. Both species usually form independent shoaling groups numbering several hundred but likely coexist for safety, particularly during these juvenile and younger, more vulnerable stages. At this time of year when the water is very high, the villagers do not do much fishing, it’s very difficult to catch fish and so when we bring in a full net, the Hemiodus do not go to waste. We leave just after sunrise the following morning after a cold night in our hammocks, the temperature at night time is drastically different to that of the day and as we move further upriver, the hours pass and the sun beams down warming us up again. We pass the Venezuelan checkpoint at San Jos and after a short time, to our right we see the Rio Guasacavi (often misspelled Guasacobe), the last river bordering with Colombia. Soon after, as we meander our way toward the mouth of the Atacavi River, we pass the discreet entrance to the Rio Temi, where Humboldt travelled in the early 1800’s reaching the Rio Negro over land via the Isthmus of Pimichin; I cant help but take a moment to feel honoured having travelled over some of the same route. We say goodbye for now to the upper Atabapo and begin our ascension of the Atacavi. We travel for several days and one notable stop is at the very last village ‘Paloma’, where there are just 36 villagers from 8 families and after seeking permission from the chief, who also allows us to stay overnight, we begin exploring yet again. As the evening approaches I am determined to find something special and I remain in the water until just before dark when the biting flies come out to join me. I persevere, and some time later my determination pays off. Just as I am ready to give in, I capture an exceptionally beautiful male Laetacara fulvipinnis, its reflective blue scales on its golden brown body are outstanding; the species was only described in 2007 and the Atacavi is a new locality for this fish within its range, it is a fantastic find for me! At every location, I take time to dive down into the biotopes to learn more about how the fish operate within their aquatic habitats. I put on my mask and swim down among the bushes and trees, to get a closer look at how the fish live and behave. In this mysterious world of sunken logs, submerged forest and varying visibility, where you can only really see clearly within about a metre (and it reduces significantly when you travel downward away from the light), there is a real sense of uncertainty and it can be a little scary if you venture too far on your own. My mind tells me “go back, you’re in the middle of nowhere!” but my heart wants me to keep exploring and around every sunken tree there is another reason to keep going. I eventually emerge and walk my way through the shallow flooded forest, caving to my common sense and trying my best not to agitate the stillness of this undisturbed habitat. I tread as carefully as I can through the water which is only about 30cm deep here and quickly spot some more fish. I watch small families of Dicrossus gladicauda swimming together in groups of five or six, but sometimes more. They have the most impeccable blood red ventral fins which I can see clearly even from above as they graze on the very fine detritus lining the leafy substrate. As the sun shines in through the tiny holes in the canopy, the sight is literally breathtaking and I feel so very honoured to have seen this place. Just to make it sweeter, I am then investigated by a weary shoal of the most gorgeous juvenile Cardinal tetras (Paracheirodon axelrodi); they are only about 15mm in size and their innocence is just adorable. They graduate toward me, each individual making its decision based on the action of the nearest group member, the tiny movements I make ripple through the shoal in a second as they react. Watching them feel their environment is inspiring and I take that away with me as I head back to the others. I only stop to observe a trio of young Biotodoma wavrini sifting through the silty substrate for food items.

The entire Atabapo is underpinned by vast areas of igneous granite rock, each time we make a stop at these rocky habitats I put my mask on once again and go exploring. The force of the river is extremely strong and any attempt to swim against the current is almost futile, but once submerged I hold onto the rock surface and clamber my way ahead. At about six or seven feet below I clasp onto the lip of a shallow crater in the rock and in the neighbouring crater find a small community of twelve to fifteen Ammocryptocharax elegans, they use the craters as temporary refuge from the intense water flow. Covering the rock is a layer of rough sponge from the family Spongillidae, these freshwater sponges have adapted to far more varying environments than their marine cousins and when conditions are not favourable, they produce buds which germinate again when the time is right; here I am able to see what I believe to be Rineloricaria grasping the surface of the sponge amidst the water flow and grazing. Roughly ten feet or more below the surface on the rock substrate are very large pieces of rock which form crevices against the river bed. Under here I am able to collect with my hands, several Dekeyseria sp (L052), the striking Loricariid which is reported to be less orange in colouration than its relative D. brachyura (L168), from the Rio Negro basin but the difference is very subtle in some individuals. They are highly communal and we find many living together and always underneath the rocks in the crevices. Not far away I also find Pseudolithoxus anthrax (L235) using its dark colouration to camouflage itself in a tight vertical rock crevice surrounded by a protective maze of tree roots and nearby submerged trunks. I begin to understand much more the significance of the biotope to each species and I ask myself if the orange striping of the Dekeyseria help it to appear less visible next to the reflective sunlight intermittently penetrating the shadows of the shallower tea coloured water and if the darker colour of P. anthrax helps it to remain inconspicuous until nightfall; After more than fifteen years worth of interest and practice with biotopes, I am once again humbled and reminded to keep an open mind. Some days later, as we head back down the Atacavi, I cant help but wish we had more time to explore this river, a week seemed over in a flash, but I am also excited to get back onto the Atabapo, it is here where one of my main interests lies. We cross back into Colombia and as we descend the river over a few more days, we continue to search many locations. In the middle to lower Atabapo we stop and I climb my way up and over the huge mountainous island at Caño Vitina, situated next to the native ‘Piroa’ community of Gualloval Vitina. I spend almost two hours diving around the perimeter of the huge island alone, the sandy substrate is hidden many metres below the high water and the space beneath me comprises nothing but granite rock shores sporadically lined with leaf debris. The water outside of the shallows is deep with only emerging tree tops visible and the rocky surface of the island has pothole formations scattered above and below the surface. In one of these small craters, less than one metre down and under a single leaf is where I unexpectedly find, Apistogramma lineata; this is a new location for this fish which is a relatively new species of exceptionally red colouration and was only described by Mesa and Lasso in 2011. They described the fish from the respective holotype and paratype locations of the caños Gaza and Chaquita, situated approximately twelve kilometres back but now we can add Caño Vitina to the list. The young fish initially hides from me, but as I slowly lift its protective leaf hideaway it looks directly at me almost as if interested. The endearing, trusting nature of the fish enables me to guide the youngster into my net and subsequently take what I believe, are now the first live photos of this species ever to be published; as a thank you, I make it my duty to return this fish to the exact place I found it before we leave for our final destination. The parameters here were as follows, temperature: 29.5°C, pH 4.29 and conductivity 12μS. As we reach the lower Atabapo, I am yet to find the species which has brought me five thousands miles across the Atlantic and so I insist on stopping at one last particular place in the hope that I can rediscover them for myself. The location is the type locality but with the high water season in full effect the chances are quite low of finding them as they usually retreat into the submerged forest to breed once the waters are high enough and do not return to the safety of the rocks until the dry season; still, I decide to try. As we arrive, our boat is surrounded by large Leporinus, Bryconops, Prochilodus and large Black Piranha that appear to be accustomed to being fed; we are even greeted once again by the beautiful and mysterious Inia geoffrensis humboldtiana, the Orinoco pink river dolphin. As we walk toward a collection of large man-sized boulders emerging at the shore, we see at the base of two palm trees a group of six to eight Uaru fernandezyepezi plucking blades of submerged grass. They scatter in a flash at the sight of potential predation from above and as I get in the water to investigate they are nowhere to be seen. I dive down to search between the huge rocks; the water is very dark and deep. To my absolute joy I am inspected by a single Heros sp., the semi adult fish is remarkably confident but as I attempt to entice him into the net, he understands that he is better off elsewhere. John joins me and we continue what seems to be a hopeless search, but as I am about to give up, my arm is tugged by John. Right next to us at about 1.5m depth, in a crevice of only 15cm, we find the majestic Pterophyllum altum. As we look down into the tiny crevice, which broadens further down, we see the shy eyes and exceptionally elongate dorsal fin of the Altum Angel looking up at us. In the dry season when the forest is not accessible, it is these rock formations in the Atabapo which provide the only safe places for this laterally compressed fish and this is the only place where this species survives this way. Having seen the Altum Angel in its habitat and spent time analysing this biotope, I am filled with immeasurable insight and I know my Atabapo biotope aquarium will never be the same once I return home.  Parameters measured here were, temperature 30.4, pH 3.7 and conductivity 12μS. As we round up the trip and head back towards Inirida, I look back and absorb the experience. I have a much greater understanding of the dynamics of this environment; the niche of each fish affects their appearance and behaviour. I cannot help appreciating the important role of each biotope as a home to specific species, which know their roles in that niche and know each other; without doubt, a biotope aquarium is the best thing you can do for any fish.

Comments 7

  1. Chris,
    The photos of the Festivum cichlid (Mesonauta egrigius) endemic to the Orinoco, and the altum angelfish (Pterophyllum altum) were spectacular. Thanks for sharing!!

  2. Wow some real info on the Atabapo Finally;
    Actual water parameters;
    Extreme low PH very interesting ; High Temp
    Makes one ponder the affect of humeric acid on water conditions ; Colours etc ;

    Thank you for sharing these insites ;

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  3. Outstanding article. Particularly enjoyed the excellent images and learning that Hemiodus gracilis and H. cf thayeria are sympatric at some of the locations described. Beautiful fish. Manhy thanks!

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