One of the best things about traveling to aquarium clubs around the world is getting to meet all sorts of interesting hobbyists. And one of the things that I'm struck by- besides the sheer number of unusual things that my fellow fish geeks are into- is a tremendous fascination with the ecosystems from which many of these fishes that we play with come from. This comes up again and again! I was speaking at a club this weekend in Washington D.C.- a club with tremendously experienced hobbyists, and the open-mindedness and fascination with this "botanical-style-aquarium-thing" was really exciting and stimulating.
One of the topics which kept coming up during and after our ensuing conversations was thinking on a deeper level about how to more faithfully replicate the natural habitats of many of the fishes that we love so much. And of course, the the idea that there are all sorts of interesting influences on these natural habitats created by the surrounding terrestrial environment and the microbial associations which occur in the substrates, leaves, wood, and other materials which comprise them.
The relationship between terrestrial habitats and the aquatic environment is becoming increasingly apparent- particularly in areas in which blackwater is found. And, the lack of suspended sediments, which create a "nutrient poor" condition in these habitats, doesn't do much to facilitate "in situ" production of aquatic food sources; rather, it places the emphasis on external factors.
Many blackwater systems are simply too poor in nutrients to offer alternative food sources to fishes.The importance of the relationship between the fishes and their surrounding terrestrial habitat (i.e.; the forests which are inundated seasonally) is therefore obvious. That likely explains the significant amount of insects and other terrestrial food sources that ichthyologists find during gut content analysis of many fishes found in these habitats.
And, as we've hinted on previously- the availability of food at different times of the year in these waters also contribute to the composition of the fish community, which varies from season to season based on the relative abundance of these resources.
Another example of these unique interdependencies between land and water are when trees fall.
It’s not uncommon for a tree to fall in the rain forest, with punishing rain and saturated ground conspiring to easily knock over anything that's not firmly rooted. When these trees fall over, they often fall into small streams, or in the case of the varzea or igapo environments in The Amazon that I'm totally obsessed with, they fall and are submerged in the inundated forest floor when the waters return.
And of course, they immediately impact their (now) aquatic environment, fulfilling several functions: Providing a physical barrier or separation from currents, offering territories for fishes to spawn in, providing a substrate for algae and biofilms to multiply on, and providing places for fishes forage among, and hide in. An entire community of aquatic life forms uses the fallen tree for many purposes. And the tree trunks and parts will last for many years, fulfilling this important role in the aquatic ecosystems they now reside in each time the waters return.
In nature, as we've discussed many times-leaf litter zones comprise one of the richest and most diverse biotopes in the tropical aquatic ecosystem, yet until recently, they have seldom been replicated in the aquarium. I think this has been due, in large part- to the lack of continuous availability of products for the hobbyist to work with, and a lack of real understanding about what this biotope is all about- not to mention, the understanding of the practicality of creating one in the aquarium.
Long-held fears and concerns, such as overwhelming our systems with biological materials, and the overall "look" of decomposing leaves and botanicals in our tanks, have understandably led to this idea being relegated to "sideshow status" for many years. It's only been recently that we've started looking at them more objectively as ecological niches worth replicating in aquariums.
The function of this habitat can best be summarized in this interesting except from an academic paper on Amazonian Blackwater leaf-litter communities by biologist Peter Alan Henderson, one that is useful for those of us attempting to replicate these communities in our aquaria:
"..life within the litter is not a crowded, chaotic scramble for space and food. Each species occupies a sub-region defined by physical variables such as flow and oxygen content, water depth, litter depth and particle size…
...this subtle subdivision of space is the key to understanding the maintenance of diversity. While subdivision of time is also evident with, for example, gymnotids hunting by night and cichlids hunting by day, this is only possible when each species has its space within which to hide.”
In other words, different species inhabit different sections of the leaf litter, and we should consider this when creating and stocking our biotope systems...Neat stuff!
So, beyond just creating an aggregation of material which imparts tannins and humic substances into the water in our tanks, we're creating a little habitat, every bit as interesting, diverse, and complex as any other we attempt to replicate. In the aquarium, you need to consider both practicality AND aesthetics when replicating this biotope.
A biotope that deserves your attention and study, indeed.
And of course, if you wanted to split hairs and really parse this stuff out, you'd probably wonder which specific leaves, seed pods, etc. are found in the habitat of the fish you[re interested in keeping. This makes perfect sense...You're likely thinking, "If I use the exact materials found in the habitats where my fishes come from, I'll likely be imparting the same compounds in the same ratios found in Nature!" (Seriously, I bet that's exactly what you're thinking!) I've spent years trying to track down some of the plants found in these locales.
And of course, there is a little problem with that. Many are simply not available outside of their native haunts. And you could literally drive yourself crazy trying to find them! We've made a great effort trying to source leaves and other botanical materials from tropical habitats around the world, with this very premise in mind. However, we've typically had to settle for "surrogates"- leaves and such which come from plants found in the regions where our fishes come from.
This returns us to the interesting question about exactly what compounds are found in what ratios from what materials in a given aquatic habitat. And even if we could source the exact leaves or seed pods or whatever- we'd at best be guessing as to how much of what they are imparting to the water. Like, will a catappa leaf collected in February from Malaysia have the same ration of tannins, humic substances and other compounds as a catappa leaf collected in India in July under slightly different circumstances? Does it matter?
Yeah, you COULD pretty much go crazy trying to do the mental gymnastics around this stuff. The reality is that the best we can likely hope for, until some incredibly detailed analysis of the water conditions in our fave habitats is done- is to simply do our best.
Frustrating, I know. However, I suppose that, until more information is unlocked, the best thing that we can do is to utilize the materials that we have available in a quantity and variety which "feels right" to us, and seems to have a positive impact on our fishes.
And to take note of our findings; our discoveries.
These kinds of interesting little ideas can occupy the imagination of hobbyists for decades! And the fact is that most of what we are doing in our little botanical-infused world is simply a "best guess" in many cases...a true work in progress. Yet, a "work in progress" which may have some profound impact on the hobby for decades.
Isn't it exciting to be on the aquarium hobby's "bleeding edge?"
Yeah, it is.
Stay devoted. Stay curious. Stay diligent. Stay excited. Stay observant...
And Stay Wet.