Tai explores a clearwater habitat on the edges of the Amazon basin, finding several of the most popular aquarium fishes during his visit.
In early March 2026, I found myself in Brazil with my good friend Juliana Leroy, exploring aquatic habitats. We had driven across great swathes of central Brazil and were now in the state of Maranhão, in the region north of one of the larger cities, Imperatriz.
Maranhão was one of the earlier states to be colonised and so has been considerably developed over the centuries. When Europeans first arrived, it was a region of mangroves, coastal forests and lush inland rainforests. Now, when looking at satellite images of the state, you can see only a few fragments of major forest cover in the west. Such holdouts are usually part of indigenous reservations, the tiny vestiges of the eastern edge of the Amazon rainforest.
We had driven north into this part of the Amazon biome in an effort to escape the rains which had impacted our initial plans to explore further south, in the Cerrado grasslands. In central Brazil, the wet season usually runs from late November to late February, petering out during March, but each year the rains become harder to predict.
This year, they were late and then extremely heavy, causing flooding and lethal mudslides. The rain continued well into March, meaning that many of the habitats along our 10,000 km route were too murky, too deep and too dangerous to get into, let alone film underwater.
I confess I was feeling pretty despondent. In 2022, on a visit to the Pantanal, it had rained heavily out of season, impacting the trip and causing murky conditions. I returned to Brazil in 2023 to explore the arid north-east with Juliana, a region, where in some places, it doesn’t rain for years. Of the fifteen days I was there, it rained for fourteen! Now, in 2026, I was again being thwarted, after spending a huge amount of time, money and effort, by the weather.
But all was not lost, as the rains meant I had the chance to explore the habitat that is the subject of today's article. A habitat home to one of the hobby's most familiar tetras, the x-ray tetra (Pristella maxillaris).
The river was swollen due to the heavy rains - All photos by Tai Strietman unless otherwise specified
Related article: Tai's step by step Brazilian tetra biotope.
Exploring the waters of Maranhão
We had planned to visit a series of natural swimming areas in Maranhão, which featured crystal clear water and dense aquatic vegetation. We found, however, that the heavy rains made them too turbid to film or explore. However, we decided to risk staying an extra day and trying ‘one more time’ before driving about 600km to an even more arid region. We visited a small private property bordering a river, and my hopes began to rise as I saw that the water seemed clearer than elsewhere.
During the night, it hadn’t rained so intensely, and even in this short time, the water was not so turbid as less soil and detritus had been washed into it. We negotiated with the lady of the house a price to spend the day by the river and for her to cook us lunch. Thunder rolled across the surrounding hills and it drizzled every now and then, but I was excited to get into the river.
Tonia fluviatilis thrived in the main channel
We explored the main river channel, where stands of Tonina fluviatilis grew along the banks and dogfish (Acestrorhynchus sp.) cruised past shoals of characins, likely a species of Bryconops. Stands of beautiful red waterlilies waved in the current and we spotted eartheater cichlids, likely Satanoperca jurupari, foraging over the silty substrate.
Creeping through the shallows, over areas of sandbanks and terrestrial plants which had been flooded by the rains, we saw Cichlasoma and Aequidens cichlids, alongside small pike cichlids and gold tetras (Hemigrammus rodwayi). There were carpets of the pretty plant Elodea granatensis, showing lovely tiny flowers.
Gold tetras lurking in submerged grasses
A trio of tetras
After exploring the main river with Mayza, my girlfriend, who also joined us on the trip, we were completely exhausted. We rested on one of the flooded sandbars, which was dotted with Carandá palms and fringed by ferns, leaf litter and beds of waterlilies.
Juliana was lying in this shallow water, looking for small fishes among the fallen branches and palm fronds. She then began to make excited noises through her snorkel and called me over to come and look. “There’s a beautiful little fish here! With a red tail!”
I lay down and peered among the tangle of botanicals. I spotted several species I recognised, gold tetras, although they were not infected with the ‘gold’ parasite, and head and tail light tetras (Holopristis ocellifera). Seeing both of these was cool enough, but then I saw what Juliana had been excited about.
There, flitting in the current, was the most beautiful x-ray tetra I had ever seen. This fish, Pristella maxillaris, is well-known in the hobby and is a mainstay of the ‘community’ fish section in many shops. I have noticed, however, that in recent years, they mostly appear washed out and pale, lacking the vibrant red tails and the yellow in the finnage, even in large, adult specimens. Although it is still a firm favourite for fishkeepers seeking a small, silver shoaling fish.
The red tail of the x-ray tetra was very vivid
The wild specimen in front of me, though small, put his captive cousins to shame. It was interesting to note that he (it appeared to be a male rather than a more full-bodied female) was on his own, with no other members of his species visible.
One of the reasons I have such a soft spot for tetras is because on the surface, they might appear as fairly nondescript, characterless creatures, but once you spend time actually watching them, you discover that they do have personality. You might have a timid one, a boisterous one, a brave individual who will feed from your hand, and the same stupid idiot fish who always dives head-first into the plants when you put your hand in the tank, where they get stuck and need you to rescue them.
Observing the x-ray tetra, I realised he was quite testy, with shimmying skirmishes and feints against the other small characins nearby. They all faced into the current, drift-picking at potentially edible morsels which floated by. Perhaps the antagonistic interspecific behaviour was part of safeguarding their ‘spot’ in the water column.
They were all sheltering in the cover of a large palm frond, hidden from avian predators and the larger dogfish which patrolled deeper water. However, I did spot a very cute ‘baby’ dogfish zipping around this area, so the danger of predation wasn’t totally absent.
Related article: Finding ember tetras in Brazil.
A palm frond lay in the crystal clear water.
Hidden beneath the fronds
Crawling around in the shallows, I found myself chuckling at the way the Cichlasoma and Aequidens cichlids would initially stand their ground, then realise how big I was and zoom away into cover. Juvenile pike cichlids would flee and hide under leaves, then poke their heads out to look at me, while the Satanoperca would glide away, leaving behind a streaming trail of sediment in their wake.
A juvenile Saxatilia pike cichlid sheltering under a fallen leaf
In one place, I spotted a small gang of Steindachnerina, with beautiful electric orange spots near the tail. When I tried to get close, they hid among fallen palm fronds. Although this habitat was not as diverse as some I had explored in the Pantanal and deeper into the Amazon, there was still a good number of species here, and they were abundant. However, there were no fishes over 15 cm (6 in), including no large Leporinus, pacu, rays or Prochilodus, which are usually present in a healthy river ecosystem.
After a while, I decided to have a go at panning for fishes with my sieve. Often, you will catch things among the plants and leaf litter that you failed to spot underwater, and this was the case when I pulled up the sieve to see something different. It was a lovely killifish, with a sort of purplish chocolate-brown colour.
I believe it was a member of the Melanorivulus genus. The sieve technique didn’t produce much variety beyond this, however, and I lamented not having a small two-person dragnet to sweep along the shallows. Nonetheless, I began to compile a list of fishes in my head that we had encountered.
Fishes found in this habitat
- Acestrorynchus cf. falcatus
- Aequidens sp.
- Astyanax cf. bimaculatus
- Bryconops cf. melanurus
- Cichlasoma cf. zarskei
- Hemigrammus rodwayi
- Holopristis ocellifer
- Pristella maxillaris
- Satanoperca cf. jurupari
- Saxatilia cf. brasiliensis
- Steindachnerina sp.
Satanoperca eartheaters stayed close to the substrate
Check out another clearwater Brazilian habitat, this time in the Rio Jauaperi
Possible Brazilian biotope
I know I can’t bring everyone to see this place, but maybe I can convince you to recreate it at home, in your own living room? All you need is a 60 cm (24 in) tank, sand substrate, leaf litter, branchy wood and a palm frond or two (garden centres are a good place to ask for these). A group of x-ray tetras, or a mix with some gold and/or head and tail light tetras would work nicely.
You could add some root tabs to the sand and include a few dwarf pond lilies – Nymphaea 'Indiana' is a nice option – if you wanted some plants. The water can be kept clear rather than blackwater and with a simple light and filter, the setup doesn’t need to break the bank.
One of the Superfish kits, such as the Scaper 90 or 140, would work very well as they come complete with all the equipment you need, apart from a heater. Years ago, I created a similar setup using head and tail light and gold tetras, alongside fake rushes, which you can find on YouTube. Now all you need to do is sit back, relax and imagine you are observing these fishes in a clear-water stream on the fringes of the Amazon biome.
For more inspiration, watch the video from this habitat below!