Rain, predators, pools...and "riffles": The dynamics of natural processes and the benefits of mimicking them in our aquariums

Wow- perhaps the longest blog title of the year to date, huh? Don't worry, it's a relatively simple thought, despite it's voluminous size...

Those of you who regularly read this column know that I like to reflect frequently on the "process" of evolving and changing aquariums over time. I view every interaction with our tanks as an opportunity to reflect, observe, and manage the long-term evolution of them.

Thursdays are  water exchange days for our office aquariums. And, rather than look at it as some task on a checklist of stuff to do, some necessary evil" chore- we regard them as... opportunities.

A water exchange represents an opportunity to refresh, reinvigorate, and interact with the aquarium on a much more detailed, intimate level. We've pointed out many times before that, in a blackwater/botanical-style aquarium, the regular water exchanges we conduct on our aquariums are, in many ways, very much a mimicry of what happens in the wild streams and rivers of the tropical world during the rainy season: New water is added to the environment, old botanical materials and leaves are swept away from their current locations, and a new set of materials are deposited in their place. More so than perhaps other types of aquariums- the practice of replacing botanicals and leaves along with new water is a significant "weekly evolution" of the environment in this style of system.

Beyond a simple "editing ritual" or an aesthetic "refresh", this is a very dynamic process, yet one which also provides longer-term benefits for the ecosystem, because, as these newer materials are deposited, they not only help "reinforce" the matrix of botanicals already in place, they provide new "structure", new foraging, new chemical inputs (like tannins and other organics), and provide fresh material for the continued development of food webs, starting with microbial life and fungi, to algae, and on up to insects and crustaceans, which form the "backbone" of the diet of many of our fishes which hail from these habitats.

In nature, the rain also effects the depth and flow rates of many of the waters in this region, with the associated impacts mentioned above, as well as their influence on stream structures, like submerged logs, sandbars, rocks, etc. Much in the way we might move a few things around now and again during maintenance!

And stuff certainly gets moved around, re-distributed, and otherwise affected in the wild as a result of rain!

For example, seasonal water levels can rise up to 20 meters (65 feet) in the middle Amazon region! That's a lot of water! Towards the mouth of the Amazon, the yearly change becomes less and less, but even near  the Rio Xingu, it can still be as much as 4 meters (12 feet). This seasonal deluge has huge impact on not only the physical structure of the associated rivers, streams, and their surrounding forest terrain, but on the fishes and other creatures which reside in them.

Amazonian streams typically feature two interesting biotopes that we haven't really discussed in much detail here, and both of which are quite profoundly impacted by the seasonal rains: Pools, with slower current and a substrate covered mainly by deposits of leaf litter, detritus and driftwood; and "riffles' (defined as shallow sections of a stream with rapid current and a surface broken by gravel, rubble or boulders), with a moderately-fast-flowing current and mostly sandy bottom with tree roots, driftwood pieces, and small rocks and pebbles. (ohh...home to Darter Characins!) These riffles are considerably more significant in the wet season, when the obvious impact of higher water volumes are present.
And interestingly, you'll find an unexpected abundance of some species familiar to us as hobbyists in these riffles. Species like Pyrrhulina brevis, Hyphessobrycon melazonatus, and Hemigrammus of various forms, and even some Nanostimus marginatus and the killie Rivulus compressus! I find this intriguing, because we tend to associate a lot of these little fishes with sluggish water and more static environments, not areas exposed to greater current and movement. 
I pose the question once again (which we sort of hashed out on Facebook last week):
Do we need to consider applying larger volumes of "intelligent" water movement to our typical freshwater aquariums? I believe that the answer might be a resounding yes, and point to the observations about the physical habitats above as a model.
Oh, back to those Amazonian pools...
Interesting "factoid": Some scientists have postulated that the higher presence of nocturnal predators in the pools might increase the number of species that seek refuge in the riffles to avoid them! And Rivulus, which usually live in more intermittent pools along the stream edges, outside the main stream channels, are normally found at night in these riffles!  
This makes a lot of sense, right? I mean, it's a lot harder to catch your dinner when you have to contend not with the current as well! Quite a defensive mechanism!
(pic by Clinton and Charles Robertson under CC BY 2.0)
How can we as hobbyists use these kinds of pieces of information to create more realistic closed ecosystems for our fishes?
At the very least, I think it important to continue looking at our water exchanges and botanical additions/removals in the context of how natural bodies of water actually function. Such a point of view will keep our minds open and senses attuned to the evolving habitat within that glass or acrylic box which our fishes call home.
Change in these habitats is constant. Adaptation by our animals to them is as well.
Interesting stuff to ponder, isn't it?
Stay observant. Stay curious. Stay contextual. Stay excited.
And Stay Wet.
Scott Fellman
Tannin Aquaitcs 

Scott Fellman
Scott Fellman


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