Have you ever heard of an igarape before?
It translates roughly as "canoe road" in the Hengatu dialect of the Tupi language (spoken all over the Western Amazon region), and that's just what it is: A little jungle stream that is used by indigenous people in Brazil to navigate through the rain forests in their small canoes.
These little bodies of water flow between forest trees, and often diminish to even smaller shallow creeks during the dry season. The lighting is rather dim, as the sunlight is often partially obscured by the low, overhanging trees and vegetation. As one might guess, these little streams often have botanical materials, such as leaves, seed pods, and branches falling into them throughout the year.
And of course, as you also might imagine, we're more than just a bit interested in the biology of these little streams, and the implication for us as fish keepers! They provide a very interesting subject for us to attempt to replicate to some degree in aquariums.
The igarapes are home to a large number of characins and Loricariidae, yet also include some fishes like Knifefishes, cichlids, and even some killifishes from the genus Rivulus as well. If you're thinking what I'm thinking- and I'm pretty sure that you ARE- then you're already trying to figure out how to plan your next cool Amazonian-themed aquarium!
Obviously, we can take some "artistic liberties", being in this for fun and not try to be 100% biotope-centric, down to the last rock and twig. However, there are some general physical characteristics of these small streams that we can use to help us plan our little representation of them!
Water movement: Generally, a very modest current, without significant surface movement. This makes sense, because you do find a fairly large number of surface-active Hatchetfishes, like Carnegiella myersi and Carnegiella strigata in these streams, along with the aforementioned Rivulus, which tend to accumulate at or near the surface.
Lighting conditions: Rather dim, as the igarapes tend to be located deep within the forest, with little sunlight filtering down to the forest floor. You could easily get away with room ambient lighting, or maybe just a few daylight-flavored LEDs to simulate beams of sunlight penetrating the canopy. As you might suspect, there is virtually no aquatic vegetation present. Hardscape lovers, rejoice!
Water chemistry: You guessed it- soft and acidic, with pH ranging from 4.8 to 6.2 in some locations studied by scientists. There are both blackwater and "clear water" igarapes, but as you might imagine, the blackwater ones tend to be more common. High heterotrophic activity by microorganisms, bacteria, fungi, and algae tend to assimilate many of the available nutrients rather quickly.
Leaf litter: An important part of these little streams is the abundant presence of fallen leaves from the overhanging trees. These fallen leaves contribute not only tannins and humic acids to the water, they provide much of the food sources for the aforementioned fungi, bacteria and algae present in the water. There is actually some evidence that some fishes may actually consume some of the leaf litter materials as part of their diet (Walker, 1990), in addition to detritus, insects and other small crustaceans.
Botanical materials: Of course, with all of those trees, it only makes sense that you'd find some seed pods and the aforementioned leaves in the water! I know a source for materials such as those, by the way...
As for modeling your aquarium after an igarape, you can see that these are pretty interesting biotopes to imitate! Since most of these waterways are rather shallow, I think that a shallow, wide aquarium would be cool to play with. Filtration could be via canister filter or outside power filter, with either set for minimal surface disruption. For substrate, I'd use a very fine, light-colored sand. And, as mentioned above, lighting is not a major consideration, other than for aesthetics.
It's perfectly acceptable to throw in a few pieces of cool driftwood to represent the branches and logs that occasionally find their way into these bodies of water. Minimal rock is recommended, as you don't find a ton of rocks in this environment.
Okay, about all I did here was hopefully whet your appetite, or open your eyes up to consider yet another biotope to experiment with. And that's my goal. There is a lot of good research material out there on the internet about these environments.
The opportunity for creativity and education here is pretty significant, hopefully bringing some attention to this unique environment from the Amazon!
Stay adventurous. Stay curious. Stay creative.
And Stay Wet.