I don't usually make claims, but I will bet that I probably talk more about detritus than anyone else in the aquarium hobby...And I'll go out farther on a limb and claim that I probably have more good stuff to say about detritus in the context of our tanks than just about anyone in the aquarium hobby!
I've covered the topic more times than I care to repeat, but, let's face it- detritus is an essential and important component of the botanical method aquarium, and it's been maligned and misunderstood over the years.
Ecologists define detritus as, "... partially decomposed organic matter from plant and animal tissues, in addition to microorganisms and minerals."
The Aquarium Wiki (a nice source for the hobby) has a less nuanced definition:
"...dead particulate organic matter. It typically includes the bodies or fragments of dead organisms, as well as fecal material. Detritus is typically colonized by communities of microorganisms which act to decompose or remineralize the material."
That's a pretty thorough definition, isn't it?
Note that nowhere in either definition do you see references to the stuff being "dangerous" or "detrimental" to fishes or aquariums. Now, look, having an excess of just about anything accumulating somewhere in the closed environment of an aquarium has an impact that you'll have to deal with somehow, or at the very least, have an understanding of.
I know that uneaten food and fish poop, accumulating in a closed system can be problematic if overall husbandry issues are not attended to. I know that it can decompose, overwhelm the biological filtration capacity of the tank if left unchecked. And that can lead to a smelly, dirty-looking system with diminished water quality. I know that. You know that. In fact, pretty much everyone in the hobby knows that.
Yet, as a hobby, we've really sort of heaped detritus into this "catch-all" descriptor which has an overall "bad" connotation to it. Like, anything which is allowed to break down in the tank and accumulate is bad. Anything that looks like "dirt" is...well, "dirty", dangerous, and should be treated accordingly.
Now, "dirty-looking" and "dangerous" are two very different things, right? Do natural habitats look "dangerous" to the life forms which reside in them?
In botanical-method aquariums, if most of what is accumulating in your mechanical filter media and on the substrate, etc. is just broken-up, decomposing bits of botanicals, I'd have little concern. That's what happens to terrestrial materials in an aquatic environment. It's normal for these types of aquariums. As we've discussed ad infinitum here, various organisms, like fungi, etc., work to break down these materials and begin the decomposition process.
Now, if it's uneaten food that you're seeing accumulate in excess, then you need to figure out a more accurate feeding approach. Same with fish waste. At the very least, you likely need better circulation and mechanical filtration within your system. And of course, you need to address why it is you have so much uneaten food accumulating in your system!
Left unchecked, accumulations of uneaten food and fish waste can tax the biological filtration capacity of your aquairum .
"Detritus" in general, in my opinion, gets a kind of a bad rap, as the bulk of it is really broken down already by the time it accumulates in the aquarium. And there is a valid argument that this material, if allowed to settle in the aquarium, becomes a basis for biofilms/fungal growth- part of the "food web" in our tanks. Think about this: Organisms which function as "decomposers" take up substances such as nitrate and phosphate from the surrounding waters while utilizing detrital material to build new biomass! It's important for them...and for the ecology of your aquairum.
The biomass in detritus can oxidize dissolved organic compounds and ammonia and convert them into relatively harmless gases and nitrate.
And, when we value and accommodate beneficial microorganisms, we help them make detritus more palatable to detritivores! So, in an aquarium which encourages the growth of bacteria, fungi, copepods, etc., the organic material contained in detritus becomes part of the food web. Everybody up the food chain can benefit from the stuff.
By going "full ham" and siphoning every last speck of detritus in our tanks, your essentially breaking this chain, and denying organisms at multiple levels the chance to benefit from it! And, you're effectively destroying an established community of microorganisms which serve to maintain high water quality in the closed environment of an aquarium!
"Anomalous" ammonia spikes and such often have their origin in over-zealous cleaning of aquariums and filter media. Taking out all of the "fish shit" is actually removing a complex microbiome that's keeping your tank healthy!
I've seen numerous articles over the years denouncing detritus as a "nuisance", and then in the same article, acknowledging that it can be "useful" if you keep plants, or are raising fry, or keeping fishes which graze on the stuff...
The "bad" narrative seems to win out, though.
Ask yourself this: If detritus is sooo bad for fishes, how come the standard "beginner's advice" for years has been to "inoculate" your new aquarium with filter media or substrate, detritus and all, from an established, healthy aquarium? I mean, c'mon!
The indictment in most of the articles that I read on the topic is that it's "bad" for indeterminate reasons, and that you should remove it from your tank because it "looks bad."
That's not exactly a scientifically compelling reason to eliminate detritus from your tank, is it?
About the best case I've seen to not have excesses of detritus accumulate in a typical aquarium is that they do contain bacteria. And, for some fishes which continuously come in contact with it, like bottom-dwelling catfishes, it requires them to mount a bit of an immune response to the bacteria (harmless or not) contained in the detritus, leaving their immune systems taxed and slightly less "available" to resist legitimate illnesses. Perhaps a bit of a "stretch", but it seems to make some sense to me.
That being said, I wonder how much of this stuff is really accumulating in a well-managed, under-populated, and carefully-maintained aquarium? Sure, in systems with large, predatory cichlids and messy eaters, you're likely to see a lot more than you would in a lightly-stocked tank with say, Endler's Livebearers or Gouramis, but still...do most of us really overfeed THAT much?
I don't think so. I mean, I hope not.
Of course, if you see uneaten food and such accumulating in your tank, it looks crappy. It's a sign of poor husbandry. With this undefined "detritus" that you may see, however, do you have phosphate or nitrate issues as a result of accumulating organics from this stuff, or is some of it- enough of it- being utilized by bacteria and other "unseen residents" of your tank that it's not really a "problem" from an environmental standpoint? What does the test kit say? Do you have massive excess algal growths? A depressed oxygen level in the tank?
Or does it just look sloppy?
Is this another case of us in the aquarium hobby making a grand pronouncement like, "It looks shitty, so it's always bad!" yet again?
I think so.
Ahh, "detritus"- menace or benefit? Or perhaps, something in between? Like biofilms, fungal growth, aufwuchs,and decomposition- is it something that is inevitable, natural- perhaps even beneficial in our aquariums? Or, is it something that we should learn to embrace and appreciate? All part of a natural process and yes- aesthetic- that we have to understand to appreciate?
The natural habitats seem to have plenty of it.
Fellow hobbyists keep asking me my thoughts about detritus, and I admit, they have evolved over the years. I think so many things in moderation are pretty good- even things that we have historically "freaked out" about. Yes, hardly a scientific conclusion, but I think valuable from an aquarium management perspective.
It's about moderation. It's about going beyond the superficial.
Part of it is a "mental shift" that we have to make. Again. Understanding that, in Nature, detritus is abundant, common, and vital to the health of aquatic ecosystems.
Let's shift our focus just bit to one of the more "practical applications" for detritus- as a food source for fishes.
To a certain extent, detritus is a part of the diet of almost every fish. If you're into reading and studying gut content analysis of fishes like I am, you'll see "detritus" mentioned in virtually every single one. The percentage of the diet that detritus comprises varies from species to species, but it's ubiquitous.
And of course, if you observe the behavior of many of your fishes in the aquarium, such as characins, cyprinids, Loricarids, and others, you'll see that in between feedings, they'll spend an awful lot of time picking at "stuff" on the bottom of the tank. In a botanical method aquarium, this is a pretty common occurrence, and I believe an important benefit of this type of system.
I am of the opinion that a botanical-method aquarium, complete with its decomposing leaves and seed pods, can serve as a sort of "buffet" for many fishes- even those who's primary food sources are known to be things like insects and worms and such.
Well, I may favor little fishes like characins and Rasbora in my tanks, but I do have a healthy respect-and admiration for some of the more- shall we say- "hardcore" fishes...like the so-called "Eartheaters" (families Acarichthys, Biotodoma, Geophagus, Guianacara, Gymnogeophagus, and Satanoperca).
I'm asked a lot ab out keeping these fishes in botanical-method aquairums. It seems to me they'd be pretty good inhabitants, actually! And no discussion on detritus would be truly complete without talking a little about these fishes.
This lively and diverse group contains some of the most endearing and interesting cichlids around. With a surprising number of our customers wanting to incorporate botanicals in setups with these fishes, I had to chime in here in "The Tint", right? And since they tend to be associated with detritus....yeah.
(Gymnogeophagus balzanii. Photo by CHUCAO, under CC BY-SA 3.0)
And of course, the name of the genus Geophagus contains the Greek root words for "earth" and "eat", as if to reinforce the popular collective name. So, in case you haven't figured it out by now...they dig in the sand to get food...oh, and they shit....
But you probably already knew that, and, not exactly known for my love and devotion to cichlids, I'm like the last guy you really want to write one of those "Review of the Eartheaters"-type articles, so we're going to focus more on the interesting dietary preferences of these fishes, and the kind of environment you'd want to create in your aquairum for these bad-asses, from a botanical perspective, of course.
First off, let's talk about their diet.
These fish ingest just about any decomposing material...leaf litter, botanicals, etc... that they can. They sift through it and other materials in the substrate to derive their nutrition. And, if you go just a bit deeper than you see on the typical hobby website information...
What do they actually eat in the wild? Well, here is another one of those trusty gut content analysis which I found in a research paper on a few species of Geos:
Insects (terrestrial). 6.5%
Trichoptera larva 6.5%
Chironomidae larva 2.33%
Coleoptera larva. 3.83%
Coleoptera adult 3.83%
That's a LOT of detritus!
Detritus is an extremely "available" food resource, not subject to seasonal and regional shortages and other factors. It's everywhere, pretty much all the time. Because of its composition, detritus is something that has been available as a food resource for fishes for untold millennia. Water chemistry and seasonal availability WILL at least impact the composition of the detritus at any given time, but that's about it. Detritus is a really good food source!
Detritivores, in general, are responsible for the fragmentation of plant and animal debris and conduct what ecologists call "inoculation" of the rejected material with microorganisms that complete the decomposition process. And of course, that makes nutrients from detritus available for plant uptake within the ecosystem.
Detritivorous fish have physiological adaptations in the digestive process to extract large amounts of nutrients from detritus, since it provides less energy and protein than other types of food. The digestive tract of detritivorous fishes is characterized by a small, muscular stomach, and an extremely long intestine, to facilitate a high rate of absorption and assimilation of nutrients by the fish. According to ichtyologists, this characteristic long intestine can vary from 3 to 10 times the body size among detritivorous species.
The elongated intestine is curled and folded extensively to fit inside the body cavity, which results in a long intestinal contact and passage time. This effectively keeps the ingested detritus in contact with digestive enzymes for an extended period of time, ensuring the maximum possible extraction of nutrients by the fish.
In wild aquatic habitats, detritus is comprised of many things; however, in places like the Amazon basin, it's been determined through gut-content analysis that a high percentage of the detritus consumed by fishes is composed of plant materials- leaves, seed, and wood, as well as components of terrestrial grasses, like Paspalum, which is abundant in this region.
Geophagus are what are known to scientists as "benthopagous" - meaning that they derive most of their nutrition by ingesting large amounts of substrate and sediment, and sift for food organisms and detritus, expelling the undigestible material through their mouth and gills.
Hence, the origin of the popular name, "Eartheaters!"
While these fishes do ingest detrital material (which isn’t particularly nutritious), they do so mainly to consume and assimilate the associated microbial growth in the detritus.
Now, let's be perfectly up front: These are larger, messy fishes. If you're thinking that you can create a beautiful, elaborate aquascape for them, and that they would leave it nicely intact, you're in the realm of fantasy. They will spend large parts of their day digging and sifting and upending whatever is in their way.
You need to accept a different sort of aesthetic: The one that the fishes will create, wether you like it or not! One that will have substrate continuously moved about, and whatever material is contained within the substrate either put into suspension within the water column, or collecting on the surface of the substrate. Good circulation and filtration are essential.
(Gymnogeophagus balzanii. Photo by CHUCAO, under CC BY-SA 3.0)
It means oversized filtration- likely canisters, or even the newer automatic filter roll systems in a sump (this would be the best way to filter a system containing a population of these fishes, IMHO.)
I wouldn't even attempt to keep these fishes without radically "over-filtering" their aquarium. It will just keep you from going crazy.
Now, that being said, if properly filtered, you could - and should- include botanical materials and leaf litter in their aquairums. What? All of the "experts" say no way? Okay, have the experts actually kept their tanks with these fish with an automatic filter roll and leaf litter and botanicals?
Yeah, I didn't think so.
Besides, these fishes will absolutely ingest large amounts of leaf litter and other botanical materials to derive some of their nutrition, as we discussed above. This is what they do in the wild. It's what they're evolved to do. We just need to manage our expectations and consider how an aquarium designed to accommodate voracious detritivores looks and should be run for long term success.
(Satanoperca leucosticta- image by Dr. David Midgely, used under CC BY-SA 2.5)
As you know by now, many botanical materials have significant amounts of lignin and cellulose, which are thought to be necessary for the health of these fishes.
So, yeah, why NOT try to keep Geos in a botanical-method aquarium? Damn, I can't believe that I just devoted a fairly respectable amount of time to discussing Geos in "The Tint!"
However, it was in relationship to my main argument about the usefulness of "detritus" in our aquariums. The bottom line (pun intended) is that I don't see detritus as a "nutrient trap" in the aquarium.
Rather, it's it a place for fishes to forage in and among.
A place for larval fishes to seek refuge and sustenance in. Kind of like they do in Nature, and have done so for eons. Yes, we're talking about a closed ecosystem here, which doesn't have all of the millions of minute inputs and exports and nuances that Nature does, but structurally and functionally, we have some of them at the highest levels (ie; water going in and coming out, food sources being added, stuff being exported, etc.).
I think we really need to think about our systems- particularly in the botanical-method aquarium world- as little microcosms, which replicate- at least on some level, some of the process which occur in Nature to create a specialized but highly productive and successful- not to mention, dynamic- ecology.
There is so much more to this stuff than buying in unflinchingly to generalized statements like "detritus is bad."
It's a mental shift.
One which we should all consider making.
Stay thoughtful. Stay curious. Stay open-minded. Stay adventurous...
And Stay Wet.