Article © Julian Dignall, uploaded November 22, 2020.

Prologue
What's on your "bucket list"? What experiences would you place highly or those that you'd dearly like? I must confess that visiting the Rio Xingu in Brazil was high on my list, not top of the list, but certainly high on the places I'd like to see that don't require hitchhiking across the galaxy.

That might seem an odd turn of phrase, but some readers may be familiar with the work of the famous British author Douglas Adams who, before his untimely death in 2001, wrote a series of satirical science fiction novels which have been made into successful radio and TV programmes, movies and computer games. Adams's delightfully British dark humour can also be found throughout one of this lesser-known books called "Last Chance To See". In essence, it's a nature travel book but one where Adams, along with fellow traveller the naturalist Mark Carwardine, recounts his meetings with several species at the front of the queue for the extinct section of the Earth's bestiary. It's a great read: sobering and funny - I highly recommend it.

I ended up prioritising the Rio Xingu (pronounced shin goo) in my thoughts because it seemed that, with the construction of a hydroelectric mega dam on the river, that this was my last chance to see. The time left to experience this habitat, and its fishes, in the state they've been for hundreds of thousands of years, was rapidly diminishing.

Most aquarists have been aware of the dam threat facing many of the fishes we enjoy keeping and breeding at home for a long time. While captive breeding programmes may sustain some of the more attractive and easier to breed species from threatened areas, the habitats and the more obscure fishes may no longer exist. My interest was understanding the river a little more in order to better recreate it at home but also to document what I could for future generations who may not be able to witness it.

In 2013, I started a fundraising campaign which ultimately provided technical and camera equipment used by researchers studying the fishes and their watery homes. Working with the local ornamental fishermen much progress has been made in dissipating the large amount of accumulated myth and misunderstanding how these fishes live and reproduce in nature. These amazing plecos and other representatives of well over 400 species of fishes from the river have been exported from the town of Altamira since the 1980's. The place has been beckoning me since then and I finally got my chance to travel there in 2015.

Good morning Brasilia!

Getting there
My travel to Brazil was uneventful. On the way out I routed through Amsterdam, Sao Paulo and then on to Brasilia where I was to overnight. There are only a few flights to Altamira each week, so I wanted to ensure I did not miss it. I wake up in Brazil, there is a first time for everything. Contemplating the day I get to see the Xingu, I think there is a risk of not getting much to eat until late afternoon. So, after a few practice runs I try my hand at ordering room service. I enquire if the member of staff can speak English ("Voce fala engles") and the response is a kind "Nao". Right then, I order "Café del manhã" which is a simply breakfast and manage "oyto zero tres" for my room number. I end the call with an "obrigado" which is simple to say if you have a Scottish accent and know to put the emphasis on the third syllable. Indeed, much is gained by listening and copying. It was worth the effort, the breakfast that arrived would have fed a family of four. This is not a country with a shortage of natural resources, indeed it has them in abundance.

Heartily fed, I fly from Brasilia to Altamira. The latter's airport is a small affair; the runway is packed red dirt. The landing was good, but you get a clear sense of being in a flying bus. We disembark, well many of us do, some will stay onboard as the flight will turn around and fly to a second and then third town before returning to Brasilia. The exiting passengers cram into baggage reclaim and we grab our bags and head outside. The airport is not much bigger than a large petrol station, so I'm quickly straight out on to the street. It's tricky to get to Altamira from Europe in a day, my trip took two. For the fishkeeper, it is useful to consider that all these exotic plecos from the river do the reverse before they reach us, usually with much longer layovers. So, when buying them, consider this and don't expect them to immediately do well in a bustling well stocked tank unless you know they've already been fully acclimatised to life in the UK.

Leandro's lab from outside - funded by the belo monte dam project

Altamira
To the newcomer, Altamira is dusty, some buildings appear half-finished or decrepit. If you've done this before the restaurants hold intrgue, bars look inviting and most shops look great and oftentimes useful to the aquarist abroad. I'm still fuelled by the breakfast of several champions, so transit is comfortable. There is a lot of dam related infrastructure construction going on but it otherwise looks quite like much of semi-rural South America. I glimpse the river from the road which just builds to a sense of anticipation. People are happily going about their business as we drive to the University facility - I am a guest of Professor Leandro Melo de Sousa. The University grounds have some new single storey buildings which house Leandro's lab and other related areas where specimens of fishes are researched. The University is to be our base and I quickly unpack my rucksack.

Off the side of Leandro's office is a large room of racks filled with jars of unidentified species many of which are undescribed. I wonder if it is the largest collection of new ichthyotaxa in the world. It might just be. There is a smaller room with even more jars of fishes and plastic casks too. This room is where fishes are examined and sorted. There is every kind of freshwater fish here. Catfishes interest me, of course, but there are some really obscure charcidae, and most other groups of South American freshwater fishes too. We spend a lot of time just slowly looking at each preserved specimen, talking about what we know of them. To the fishkeeper, the sight of so many dead fish preserved in alcohol may seem morbid, but it's a vital part of the scientific process. Without knowing how many species there are in the Xingu, how can we say (or prove) how many are there, or are threatened or close to extinct already? A sober thought to consider is if some of these new species will be described after they are forced into extinction in the wild.

In the lab, hundreds of specimens await examination and classiciation. This is where new species are 'born'

These jarscontain fishes only from the local area, nothing in this rack was known to science a decade ago. Many in here not yet described

In the prep and examination room, this collection of only characidae await closer scrutiny

I also unpack my technical equipment bag, it has all the leads and so on for charging camera equipment. I set this up and get everything charging. There is good internet here too! So, I set off everything charging, push some pictures up to Instagram and work through a few emails. The lab (and associated breeding facility) is funded by the Belo monte dam project. I think to myself it is incredibly ironic that such leaps in our knowledge of the fishes of this area is at least in part paid for by a construction that will in all likelihood wipe many of these species out.

Before we head to the river, let me give you a little geography. The Rio Xingu is one of the Amazon river's main tributaries. It flows north and joins the Amazon main channel near the latters mouth. Some authors split the Xingu into lower, middle and upper sections. However, the upper section is some two thirds of its total length and the lower one sixth. But it is a useful term to say middle Xingu when talking about both my trip and the fishes commonly exported from Altamira. The "middle's" downstream end is the small town of Vitoria do Xingu and upstream limits are about where the river is joined by the lower Rio Iriri. Altamira is at the heart of the middle Xingu and sits at the upstream start of the so-called "big bend" on the river between it and Belo Monte. This hydrographical quirk also makes the bend a "perfect" spot for the huge damn project.

Massive granite rocks rounded by the ages and lined by high-water levels, the cracks and fissures you see above water are the same below

This 30ft tall rock is smoothed to the point of appearing wet and oily, it is bone dry and covered with holes and crevices

But why this river, what makes this a special place? I can answer that in one word, rocks. You can't go anywhere on the river and not be surrounded by them. And they are as odd as they are omnipresent. Obsidian lateritecontaining yellowish orange quartz and brown or black granite intermingle and have driven evolution of the local fishes. Over these same millennia, the river Xingu's waters have shaped these rocks and the resulting biotope is like no other I've encountered in South America. It's all about fast, warm clear water roaring past rocks. Often these rocks are isolated, almost reef like. It is hard to find any aquatic vegetation and the biotope is rocks from the size of a marble up to the size of houses rounded by the ages in very weird ways. We find vertical tubes or bowls formed by a hard rocks spinning in the current and drilling into a softer rock, unable to escape just being spun around in the current, year in, year out. Particularly when the river is low there are islands and rocky outcrops everywhere. They make it hard to visualise the banks of the river, often you think you're looking at one side of the river or the other only to go there, disembark and then see that there is river on the other side of the island you are actually standing on. The rocks and clear water combine to make, like snowflakes, seemingly infinite variations on a theme which are bonkers, fascinating and otherworldly beautiful. Much like the fishes that live among them.

Back in Altamira we finish packing for our first trip which is to be our furthest upriver to where the Xingu meets the Rio Iriri. It is now night time and we head out to dinner the food is delicious, I especially recall the fish nuggets (Cichla sp.) The others have meat dishes, with fries or beans, a little salad. There are no sauces on any of the meat. We drink bottles of Stella Artois served in ice buckets while sitting out on the pavement in a long table and the conversation is excellent, light hearted, the stuff of travellers getting to know one and another. We walk back to the University, a favourite thing of mine is the warm night in the tropics, the sound of crickets and even in a built up area like Altamira, it is calming and makes me feel good. Turning in, I set the alarm for 0630 and my mind drifts off to thinking about the Rio Iriri.

I first read that word in the previous millenium, it was in the first Aqualog l-numbers book. It seemed incredibly exotic, not that the Xingu wasn't exotic enough but this place was where some of the amazing l-numbers that were so rare came from. Over time, gathering the experience of others and certainly having visited now it, I think much of that was fisherman or exporter originating myth. It's a long trip from Altamira to the Iriri by boat, so not one frequently made. For the fishermen, making the trip would need to be worthwhile and also a little bit of misinformation never hurt keep the locality of a good collecting site secret. A classic example of this is the 1991 scientific description of the zebra pleco, in it, the collection location of the amazing new black and white pleco is given as "about one-hour journey by speedboat downriver" from Altamira. Actually, it was one hour upriver. There aren't really any extra special plecos found in the Iriri and nowhere else, but the legend has funded many a multi-day cachaça fuelled fishing trip.

The alarm goes, not much happens while we gather for a couple of hours culminating in a two-minute drive to the harbour laden with gear. We load our things onto two boats and wait for a while more. There are Brycon and Geophagus swimming around the boats entertaining us Xingu newbies. The water is warm and wading in it is pleasant. Finally, we get going. Two boats, the first with several barrels of fuel, tech equipment, four of our party, a fisherman and a pilot. I travel with my friend Peter Petersen of the Blue Planet Aquarium in Denmark and Nate (a local ornamental fish-fisherman), the cook (who apparently doesn't like cooking) and the pilot. The boats are long and narrow but can sit three abreast. As with most riverboats, they do not sit high in the water. Ours has a 115bhp outboard motor on the back, they can go pretty quickly which is good as we are heading upriver for three or four hours and the current is strong.

Classic Xingu biotope. Sand, sun cracked granite rocks and obsidian laterite which provides an otherworldy feel

Rocks and clear water - this is Xingu

The river has so many different islands and areas. Variously we pass rocky outcrops, riffles, sandbanks and light rapids. The rocks are either black or dark brown and often set in light brown sand. Brush grows on some islands, some not. The most notably aspect of travel up river is that the pilots need to navigate the rocks. Often we would swing out to take the boat in at a specific angle to pass through a channel. The channels sometimes had faster water, so some skill was involved in getting up through them without the motor on full power. Other areas were shallow and could only be slowly passed. At one point about an hour into the trip the other boat ran around gently on some sand. The fisherman jumped out and could walk alongside the boat to free it.

Rock pooling in paradise
Mid-afternoon we approach the split between the Xingu and the Iriri and travel about 15km up the latter. The water is fast here as we approach the Cachoeira Grande ("big waterfall"). Here the water falls several meters over rocks adorned with river weed (Podostemaceae) which when moistened by the spray of the falls burst into a beautiful purple flower - it is a beautiful scene. The fishermen set about the fastest current with snorkels and cast nets. As we are here to observe and not to fish ourselves, I go snorkelling in the waters above the waterfall. The water here is clear, warm and full of rocks. As you might expect just above a waterfall, the main channel is going at quite a lick. I pop on a snorkel and mask, I go in here. It is deep too, hauling myself down over rocks, I can only get three metres down because you have to hold on the rocks going down and back up again to avoid being carried off by the current. In the current there are Leporinus. The current is really intent on taking me over the waterfalls, so as beautiful as the characins are, I climb onto dry land.

Cachoeira Grande, the furthest downriver falls on the Rio Iriri first falls looking downriver (North)
Beautiful purple and green river weed is found in bloom where waterfall spray dampens the air, out of the spray it dries to a ginger crisp	Better than any spa - this is Rio Iriri rockpooling!

Back on dry land (well, solid rock) the team are setting up a drone. Some footage from the same spot is shown here to give you a view of what the terrain is like. The footage, and all the other ariel shots shown in these articles are from that taken using a quadcopter, a DJI Phantom 2 Vision +. Which was piloted by Daniel Fitzgerald, then a doctoral student in the lab of freshwater ecologist Kirk Winemiller at Texas A&M University. Given the high costs of renting a bush plane, flying a UAV gives a similar perspective at a fraction of the cost.

Drone footage of Cachoeira Grande do Iriri

Log in to view data on a map.Google satellite map of the same area

Staring up at the drone, I realise I am out of breath and that many side pools and channels exist with lesser or no current. It is in these that I start looking under rocks. Within minutes I've seen a lot of different plecos but identifying fishes in the wild as they scoot off into the distance takes a bit of practice. In the middle Xingu it's made even more challenging, even with just plecos, by a high level of biodiversity. We are used to seeing fishes side on in an aquarium, almost like in 2D, in the wild they're in 3D, often the colours are very different and maybe also sizes are different from that which we are more accustomed to. All of the plecos encountered are exported as aquarium fishes - so what did we find?

Spectracanthicus punctatissimus

Parancistrus nudiventris

Commonly found anywhere in deep or shallow Xingu waters with little to strong current is Spectracanthicus punctatissimus. Commonly sold as Peppermint pleco due to the unusual blue tinge of their white spots, it's unclear if L016 (which has a taller dorsal fin) L030, a numberless form with no spots on the head and the described species are all the same species or not. Regardless, they are all omnivores and very successful fishes in this rocky biotope. Together with the peppermint pleco, we also find Parancistrus nudiventris or L031 (also L176, L300 and LDA04). Here in the Rio Iriri, this species is found in arguably its most attractive form with well-placed spots. The area of the river and the patterning of populations has given rise to several l-numbers in each of these species as hobbyists and scientists alike grapple with what's a species and what is a population of a species. In the ever changing waters of the Xingu, this is one heck of a conundrum even for just one species to the next. Considering all the plecos from the region is a gargantuan undertaking.

Parancistrus differs from Spectracanthicus in that the former has larger gill openings and a broader head. Spectracanthicus (sometimes still referred to as Oligancistrus - a genus created in 1989 which following a more recent scientific work in 2014 we may now have seen the end of) is a slighter fish in overall appearance. Other key external features are similar - so use the gill shape as the best ID feature.

Both of these species are easy to keep. They are omnivores evolved to munch through the thin layer of mulm and detritus found on rocks extracting benefit from the tiny creatures within. In the aquarium they will eat most things and do well when fed a few times a day. Although secretive, their daily routine is to patrol around rocks, grazing away. An aquarium with a several rounded rocks placed so as to give plenty nooks and crannies will make them feel at home. Although a warmer temperature is preferred, they are adaptable to slightly lower (to around 77°F).

Baryancistrus xanthellus underwater habitat

Baryancistrus xanthellus adult

Chief amongst the catfishes exported only from the Rio Xingu is the gold nugget pleco, Baryancistrus xanthellus (L018 - juvenile, L081 - fine spots, L085 - adult, L177 - large spots). They are everywhere; while snorkelling it is common to encounter larger ones of about a foot in length. These armoured and spiny adults do not have much to worry about except humans seeking a tasty dinner. As an aside, I did eat the local speciality of gold nugget pleco boiled whole in a tasty broth. Texture wise the meat is similar to monkfish (Lophius spp.) and is delicious. In doing so, one inserts a fork or similar about two thirds of the way down the underside of the fish, prise apart the armour and the whole tail flesh of the fish comes out in lovely chunks. Some report it is more of an acquired taste, but I think it's down to the broth and especially the cook - ours was both modest and excellent and I think she enjoyed seeing me munch my way through two whole ones.

Indeed, gold nuggets are perhaps a better food fish than one for the aquarium. They are exported and popular because of their colouration but they are hardcore detritivores. You can see large areas underwater where they have hoovered up all the mulm covering the rocks. This isn't algae but a biofilm which is poor in nutrients, so the plecos have to eat constantly. As they can be found in even just a couple of feet of water, the presence of adults is suggested by tell-tale mini pyramids of faeces dotted around the place. In the aquarium, smaller specimens will eat most foods, but many aquarium foods can be too rich for their incredibly long intestines (evolved for intensive processing of nutritionally low yield biofilm) and so they are prone to bloating. Furthermore, to get them to grow well food needs to be more or less always present. This is hard to achieve in captivity. Gel based foods are your best bet, but this requires some dedication on the part of the aquarist. For the majority, there are many just as attractive or prettier species from the Xingu that are more rewarding (they grow more readily and can reproduce without much effort) and simpler to house.

Also in the rounded cobble biotope above the Iriri falls we found Ancistrus ranunculus, the Medusa Pleco. This is a remarkable bristlenose, it has the flattest body and widest head of any Ancistrus. Although adult males sport an astonishing array of fleshy head tentacles, unusually in the group of fishes, the females to a lesser extent, also have these appendages. Scientists theorise this is to mimic newly hatched fry, to make alpha males look like the good fathers they are and so to attract several females in succession to the spawning caves this ensuring genetic diversity. This fits with observed Ancistrus behaviour in the aquarium, although it doesn't quite explain the oddity of the bearded female medusa plecos. I had several "eureka" moments in the Xingu where I understood something more about a fish because I saw how it lived in the wild. The first was finding out why this pleco is so flat. It, and other flatter species such as Hopliancistrus sp. (L017) and Pseudancistrus sp. L067 lives in cracks in rocks. I should explain the cracks. These are not holes or gaps between rocks, these are where one particular type of granite found through the Xingu splits. It is a fissure, you can see this readily above water, below, it forms a specific habitat for many fishes and is where they live during the day.

Spectracanthicus zuanoni

To my eyes, the most attractive species we found in this habitat (and remember there were lots of cichlids, characins, freshwater rays and other catfishes - I am only discussing the plecos found commonly in the biotope and exported) was Spectracanthicus zuanoni (L020, L354). L354 is a larger blotched form found in this area of the Xingu, L020 is the more commonly exported form from the waters around Altamira. Its base colouration is olive green, but with large pale spots or blotches which cover more of the body than the base colour. There is a burnt red band in the otherwise obsidian eyes which are relatively large adding to the character of the fish. Intriguingly it shares the unusual green-with-large-spots colouration with a species of Baryancistrus (L019) with which it is both found in the wild and can be mixed with in exports. Perhaps this is a "strength in numbers" strategy, but I think it more likely that this patterning allows both species to feed during the day in shallow clearwater due to the camouflage it provides. The two species do not compete directly for food resources as the smaller Spectracanthicus is after insect larvae and meatier morsels with the larger growing Baryancistrus, as I've mentioned, spending its time grazing the biofilm.

Plecos from deeper water
While fishing for rays using cast nets in remarkable fast water, the fishermen collected one of the stand out plecos of the Xingu, Pseudacanthicus sp. L025. This cactus pleco is not commonly collected in a small size and specimens from around 12cm up to massive 45cm behemoths are collected in this fashion from the strongest current. I was amazed to see polka dot stingrays (Potamotrygon leopoldi) being fished from such fast water too. The fishermen explained they live here (not in the open current, but sheltered under rocks) during the day and only head to slower moving waters to feed under the cover of darkness.

In amongst the other larger plecos the fishermen caught were L017 and L048. On the face of it, two medium sized (30cm) plecos that are black with light spots. L017 is a species of Hopliancistrus. There is only one described species in the genus and that is

from Brazil's Rio Tapajos, it doesn't have the same heavy spotting as L017 but its specific name refers to three hooked spines found in the gill area of all Hopliancistrus. In an adult fish [such as that pictured] these are formidable defences indeed and something the fishkepper needs to be wary of. If erected in a net, chances are you will need to cut the fish out of the net to avoid injuring the fish. For the pleco veteran, moving such fish by hand can be easier for both parties, but it is an acquired skill and not to be undertaken lightly. L017 is a flatter species that H. tricornis, placid as plecos go and it is omnivorous and relatively easy to keep as long as you adhere to warm water, good water quality and plenty current. Consider keeping it with some tetras that can handle the current such as Moenkhausia.

L048 however is a bigger, heavier more imposing species. It is a species of Scobinancistrus closely related toScobinancistrus pariolispos (L133) from the Tocantins. We also see L253 from the Xingu which, when younger, has yellow in the fins and when older is more heavily spotted. L048 however is more commonly available at a range of sizes and its high contrast well defined polka dot patterning makes it instantly appealing. Better yet, it is a straight forward pleco to keep because it is a carnivore. In the aquarium it will eat most things offered but smaller fishes (less than 15cm) are most successfully grown on by feeding bloodworm or similar and adults like nothing more than munching their way through prawns or mussels. Such regular treats can be fed in addition to of a staple diet of sinking catfish tablets. Again, a high temperature is required and although a strong current isn't mandated, high oxygen levels considerably improve the fishes wellbeing.

Pseudacanthicus pirarara	Hopliancistrus wolverine (L017)
Scobinancistrus cf. pariolispos (l048)	Scobinancistrus aureatus

One can't mention the plecos of the Xingu without discussing another species of Scobinancistrus, the sunshine or goldie pleco,

(L014). It's one of those flagship l-numbers introduced in the 1990's upon which a new tribe of fishkeepers (who spend a lot of time keeping, caring and learning about these suckermouth species) helped create. Like other Scobinancistrus, these fishes can grow to a bulky 30cm or a little more but it is when they are smaller that S. aureatus shines the brightest. Pictured is a beautifully coloured individual just seconds after it was removed from a fisherman's net.

While the Rio Iriri is a fascinating biotope in its own right and the day I spent there will live with me forever in my memory. It is just one aspect of an incredibly variable river. Other aspects of the Rio Xingu will follow in part two and three where we find slower waters, l-numbers in unusual places and, of course, take a dive to meet the emblematic Zebra Pleco,

, in its natural home.

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