Rio Iriri biotope, Brazil


Heiko Bleher reveals some amazing new discoveries in Brazil's Rio Iriri — one of the most remote places on earth.

Amazingly, there are still rivers over 300 miles long that are completely unexplored — and I felt compelled to be the first researcher to enter one particular remote region.

Brazil’s Rio Iriri is the largest affluent of the Rio Xingú, merging 80 km/260 miles south of Altamira. The Xingú had been sampled in 1842 and later in its lower region by the Thayer expedition (1865-66) under Jean Louis Rodolphe Agassiz, and by Karl von Steinen (1855-1929) in 1884. Many more naturalists researched it in the last century, but none ventured up the Iriri. I often asked myself why. Yet once I had decided to go, I found out!

My friend Haroldo in Altamira was not surprised when I told him my goal was the Iriri. He explained that no one ever collected fish above the enormous current and cataract. The only cascudos (suckermouth catfish of the family Loricariidae) caught in recent years were below it. No one dares the upper Iriri, said Haraldo. This was my sort of challenge!

A Teleocichla species which is modified for life in fast moving water.

He knows of fishermen who collect L18 plecs in the lower Iriri, however the type locality is confounded with the one in the Xingú, and in the lower Iriri two similar species of Baryancistrus can be found.

One has a larger gold-yellow dotting and also occurs in the Rio Xingú in rock and stone regions south of Altamira — and someone has given two separate numbers for the same species, as L18 and L177.

The second species, and one found only in the lower Iriri, also has a broad gold-yellow seam in the dorsal and edge of its tail fin, but the golden points are smaller and over the whole body as Baryancistrus sp. ‘Iriri III’. This is similar to L-26 listed as Baryancistrus from the Rio Tocantins.

This Corydoras sp. ‘Iriri III’ is believed to be an undescribed species.

The journey up the Xingu

We loaded fuel, food, cameras and tanks and catch devices on to our aluminium boat and headed up the Xingú into the Iriri. But Haroldo feared for the weight we carried, saying we would never make it over the waterfalls.

After five hours Chico, our boatman, turned into the Iriri delta. The river itself is hardly 100m/320’ wide at its delta and becomes ever more narrow. A few kilometres in I asked to stop and we made our first discovery.

I saw between the stones in quite clear water Leporinus maculatus and L. fasciatus var., the same species found in the Xingú — likewise the characoids Moenkhausia dichroura and Brycon pesu.

Together with the latter were two more Brycon species: one had a transparent adipose fin (vs. jet black in B. pesu) and a black edged tail fin (vs. transparent in B. pesu). Both were about 7-10cm/2.7- 4” long, with a silver body, black humeral spot and light blue shining eye.

A third was a slightly larger Brycon amazonicus, also with a humeral spot and a black edged caudal. However the latter grows over 40cm/16”, while the other two rarely exceed 10cm/4” Why this mimicry? Who profits from whom? None of the three is a predator…

Loricaria sp.

Fish mimicry?

But that was not all. Hemiodus quadrimaculatus, never recorded before from the Iriri, was associated under a group of Leporinus maculatus and both have three bars. Was this also mimicry?

I continued diving in this clear habitat and I saw in the stone niches Panaque cf. nigrolineatus (P. sp. 1 ‘Iriri’) moving next to a dotted Leporinus species scraping the rocks, while a small group of young Crenicichla (C. sp. `Xingú’ II), with their juvenile banded pattern, swam together with Cichla temensis, also a banded cichlid, over the sandy bottom in search for food.

Further upriver we had to pass dangerous rock massifs, with passages only a few metres wide, and then spotted a sandy area on the left bank.

Here Natasha, my companion, pulled the 13m/43’ seine net with me and we caught two wonderful large Retroculus xinguensis and several light-coloured Corydoras. They were possibly C. xinguensis.

Leporacanthicus cf. heterodon 

We had another interesting fish: a bottom-dwelling Bivibranchia species with a protractile mouth, which it can extend some distance. Chico had already two large tucunarés (Cichla sp.) on a hook and dinner was secured!

Shortly after it became dark and we stopped below the huge waterfall and tented on a mosquito-invested river island. The beasts attacked while we tried to eat grilled tucunarés.

Early next morning I walked to the cataract. It was as high as a two-storey building and 100m/330’ long. How could we get over it? After breakfast we began to unload the boat to drag it empty over the rocks and lift it above the waterfalls.

First we carried all our equipment and fuel containers to the top of the cataract. It was nearly noon when we finished and started to get the boat to the top. Fortunately it was a stable craft and we were helped by four locals who were also on their way to the Iriri to catch tucunarés. They always fetch a good price on Altamira’s market.

Boat lifting became a joint venture, but the newcomers’ large wooden fishing craft was much heavier than ours. While trying to get these to the top I began to understand why a white man has never researched above these cataracts. Meanwhile the mosquitos ate us alive.

After we reloaded everything we moved on, surrounded by close primary forest. There was no human sign anywhere. The upper Iriri here is 30-50m/100-160’ wide and the water transparent. I saw a couple of Aequidens guarding babies along the stony edge and deeper, over a nest, a pair of Retroculus likewise tending their brood.

Geophagus argyrostictus

Groups of Leporinus were over round stones covered with aufwuchs and in the open water I spotted a swarm of possibly Brycon amazonicus. Along the shallow bank, below overhanging trees and bushes among thousands of leafs, dwarf cichlids, Apistogramma and Crenicichla as well as smaller characoids of the genus Bryconops, Moenkhausia, Astyanax and Hemigrammus were having a good time.

There were loricariids everywhere in the middle over the rock-covered ground and I was able to classify some undescribed species in no time. This discovery was however the peace before the storm....

Migration mass

The entire stony underground became scattered by black loricariids. I discovered later that it was a Baryancistrus species which I designated the working name B. sp. ‘1 Iriri’. They moved over the whole width in what I believed to be a gigantic migration which we could follow over many kilometres. Most were 15-25cm/6-10”.

At a small island in the middle of the river, with a high Ficus tree and its large thin roots growing underwater, I asked Chico to stop, tied up the boat in the current and dove in with my hand net. I had a young black Crenicichla, a striped Laemolyta and a dotted Leporinus, a small black characoid with a golden stripe and golden upper eye.

The latter was of the same species which in 1975 during my first Transamazonica expedition in the lower Xingú I discovered in the strong current below rocks and again in 1999, also below the mouth of the Iriri delta, and again under rock formations in the current. Does this species occur only in the Iriri and are its eggs carried downriver?

Leporinus sp. 'III Iriri' 

The fish biomass here was overwhelming. We caught like world champions for nearly one week at 15 further places over some 600 km/370 miles of river, in a paradise-like environment rarely found anywhere else. It was completely uninhabited, except for a single family of locals we found on the right bank a couple of days later.

We reached the wooden hut of local man Ben (Raimundo) in late afternoon of the third day. It lies 200m/650’ off the riverbank on a hill and on stilts. He had lived there for 16 years with his wife Luzia, his three boys and seven girls. They live completely autonomously on what they produce. During the extreme flood period, mostly occuring once a year, Ben takes his canoe and heads downriver, crossing the waterfall to Altamira.

Enormous rock massifs stood out from the water near Ben’s hut and I collected some unbelievably interesting fish. They included what was surely a new Sartor species, with an unusual mouth formation evolved to scrape off algae from the rock massifs while standing in a vertical position in the current.

So far only three kinds are known: S. elongatus (Santos and Jégu, 1987) which I had already discovered in 1983 in the Cachoeira de Porteira (Trombetas and Mapuera rivers); S. respectus (Myers and Carvalho, 1959) of the Rio Culuene in Mato Grosso (which I was also able to find in the middle and lower Xingú and now in the Iriri in community with the new species) and S. tucuruiense (Santos and Jégu, 1987) from the Rio Tocantins.

This parodontid is another fish adapted for the current.

This discovery is not only new for the genus but also from the point of view of species. Unfortunately these food specialists are just not recommendable for the average aquarist. The same applies to the fantastically coloured and very widespread species which also belong to the characoid family Anostomidae, Synaptolaemus cingulatus. The latter had been described by Myers and Fernández Yépez (1950) from the upper Orinoco. However, it does occur in the upper waters of the Rio Negro, in the Xingú, and elsewhere.

My discovery in the Iriri was new and here it lives sympatric with the two Sartor species.

I saw a multiplicity of Myleus and the well-known Myleus schomburgkii with its ‘Heckel-discus’ centre bar, and I found out that in the Iriri alone must live seven or eight species which the late characoid expert Jacques Géry wanted to classify as six different, mostly new species.

There was also one species of the rare Tometes, a bright butter-coloured one. It is a swimming dream with extremely long dorsal fins, gold-yellow tail, a black broad seam and large red anal fins.

New for science

Unfortunately we did not succeed in catching this beauty — it was too fast, every time eluding our nets. Yet still more fascinating fish came ashore. Seven different Leporinus species, and all except L. maculatus, were new for science and the fishkeeper.

First I saw a group of spotted Leporinus, which all looked the same, but swimming closer I could recognise three different species. Two looked so similar that I could see differences only by detailed observation. The third had at least three small bright red marks at its ventral side and in the lower mouth region. I thought one was L. maculatus, a widespread species found to the north, even in French Guyana, and south in the headwaters of the Xingú.

However after the catch I realised two species were involved. During their juvenile stage they resemble each other as an egg (only the new species is black at the mouth tip), but when adult they are rather different. The Leporinus group consisted of two banded species, which live sympatrically and have nine to ten black bars. One could be the genuine L. fasciatus but the other one, L. sp. aff. fasciatus, is currently awaiting description.

The latter differs by salient black points on each segment of its scale, as well as a yellow pectoral fin and a black edge briefly before the end of the caudal.

When I asked Ben if he knew something of the affluents of the Iriri, he said only the Novo would have flowing water at this time of the year. All others are stagnant or dry. Chico had however feared taking the boat further up the Iriri, as there are too many rocks and all our spares had been used. However, I persuaded Ben, who knows each stone in the water, to lead us for two more days.

Leporacanthicus sp. 'I Iriri'

Untouched beauty

We reached the wonderful merging Rio Novo the following afternoon and went all the way up to its waterfall. Here grew an enormous amount of riverweed (podostomaceae) in the fast current, with light red with rose-pink blooms. This was not only a new river but also a new paradise: another fantastic untouched area.

The hours and days spent here would fill books, but one single highlight stood out. I had learned much about Moenkhausia heikoi by Géry and Zarske, (2004) but was not able to see it during my 1975 discovery, or collecting in 1999. The species grows to almost 8cm/3.1” TL and looks stunning when adult.

This is an unusually beautiful fish and surely a future highlight for any characoid-loving fishkeeper. I found the adults only by diving 2-3m/6.5-9.8’ deep — and only between ther rock columns. They live and spawn in this hideaway in the current and their eggs are floated downriver, hatch, and some end up in the Xingú. Isolated large animals are found only in smaller groups in the lower Iriri and, if at all, in the Xingú.

That is also why professional fishermen from Altamira never collected this beauty. The catch of these samples was difficult, especially in the current between the rock massifs in the depths, as they always escape. I had caught eight adult specimens in two days. These had been the last of such rich rewards at my journey’s end.

Heiko with a large Serrasalmus humeralis.

Shocking encounter

I had a bad experience while trying to catch the only Corydoras species in the Igarapé Pebo, where I also discovered three different Apistogramma species. When I stepped with my hand net into the 2m/6.5’ broad creek I got some sudden electrical impacts.

These increased and I saw six Electrophorus electricus — electric eels — about 2m/6/5’ approaching rapidly. I have never moved as fast and I still don’t know how I escaped those volt-laden giants.

Leaping for life

On one of the Iriri’s sandbank islands I witnessed the incredible strength and agility of the night predators of the waters.

We were between large rock formations and the beach must have emerged from the river just a day or so before and many places were still wet.

Tree roots on the beach looked as if extras in a weird ghost movie, just hanging in the night air, the strong current having washed them out completely.

While night walking looking for fish, many jumped far out of the water often 2-3m/6.5-9.8’ high. They seemed to be large catfish of the family Pimelodidae and were chasing prey hard because of the dryness which was making food sources scare. It is difficult to believe the height a fish victim can jump to save its skin…

I had a similar gymnastic experience with a large Retroculus cichlid, but in daytime. As I began taking pictures of him in my tiny photo tank he jumped almost 1m/39” high into a nearby sand hole 20cm/8” deep. When I chased him he made another enormous jump, more than 1.5m/5’, directly into the river bed. I decided to photograph other larger cichlids holding them in my hand!

These cichlids have a reduced swimbladder and predominantly live near the ground regions, but can nevertheless jump spectacularly.

The last survivors

One native called Ben we met on our third dasy said that when he first arrived on his remote hillside a few other families were living along the upper Iriri.

However, because of the constant low water level, travel down and up the cataracts made it almost impossible to survive and they migrated to Altamira.

One Indian tribe, the Wokarangma, is a surviving ethnic group said to be of some 31 individuals and living deep in the forest.

Rescue drama

We had to manoeuvre our boat across a narrow passage against a strong current. Here the river forms a funnel before its waters tumble down cataracts. It looked as if this was once a huge lake on a plateau, which, during evolution, started to break across large rock massifs for several kilometres to finally drain into the lower Xingú.

Our outboard motor was unable to cope with the current and the boat bumped against rocks. We jumped into the water and I had pull it by a rope with one hand and, with the other, hold on to the rocks. Chico in the back pushed with his head, most of the time under water. He slipped away and Natasha jumped in to help. But she was swept downstream and got her leg stuck between some rocks.

While I climbed ashore to hold the boat, Chico dived back to rescue her before she drowned. I tied up the boat and ran over the rocks to search for an alternative passage. The region was full of rocky islands and, after hours of fighting this water’s tremendous power, we reached, at dawn, more dead than alive, a giant lake-like plateau.

Here the Iriri was several kilometres wide with gigantic sand islands. No wonder these masses of water have to find a way out. We fell into our tent on an island and into a deep sleep without food. We had survived! Next day ‘Paradise’ should open up in front of us.

Macaws woke us. Fog slowly lifted and the sun broke through over the crystal clear riverbed. A few Hemiodus jumped over the water surface. I saw on our sand island the dried-up nests of Retroculus and Geophagus species. These are amazing. After these fish have dug a wide hole into the sand, they carry heavy stones into it with pieces of driftwood and leaves before they start to lay.

After our breakfast I steered Chico, our boatman, around the enormous rocks. Here upriver the Iriri was slow and we could see everything in clear water. Suddenly seven stingrays appeared below the boat, one leading the other six. It looked like Potamotrygon scobina and P. motoro, but this could only be an estimate.

This item was first published in the September 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.