"The Scavenger Syndrome." It's about the "Otos"- and more.

Well, it comes up a every once in a while...That lovely aquarist debate about stuff like "scavengers"- a polarizing thing, filled with lots of opinions and dissenting views. The other day, a hobbyist asked me to join in on a vigorous group discussion about  best "scavenger" for botanical-style aquariums...and we were off to the races. 

First off- I believe that the idea of a "scavenger" fish in our botanical-style aquariums is outmoded, incorrect, and frankly, irrelevant. Yes. I feel that way. Because every single fish in a properly set-up botanical-style aquarium spends a large part of its day foraging in and among the botanicals for food sources. The microfauna and small crustaceans which make their home there also feed off of the abundant food available in the system.

So the whole idea of the need for "designated scavengers" is kind of silly, IMHO. The fishes are not "scavenging" off of uneaten food and such- they are foraging among the botanicals- like they do in Nature- to supplement the food which you provide to them.

One of those things that we as fish keepers seem to have to contend with is that decision between keeping fishes or other creatures that we in the aquarium world tend to view as "utilitarian" (i.e.; intended to be kept for a  specific purpose such as "algae eating"), or those that we want to keep for pure enjoyment, interest, or breeding work.

I call it the "Scavenger Syndrome." 

Nowhere is this more apparent than when we focus on that old "scourge" of hobbyists everywhere- algae.

The lovable, popular, but seemingly mis-perceived as "disposable", Otocinculus species is the "poster child" for this phenomenon. These are comical, endearing fish that are both misunderstood and shockingly disrespected, in my opinion.

They are not alone, of course. It's a shame that, for whatever reason over the years, we've tended to heap a lot of small. bottom-dwelling fishes as "scavengers" or assigned them the ridiculous moniker of "cleanup crew" or "janitors" or whatever, somehow simultaneously devaluing the fish and relegating them to an arbitrary  algae-eating "role" in our tanks that is both underserved and quite frankly, often inappropriate.

Sure, fishes like the Otocinculus are about as good a consumer of algal films as "they" make- but to purchase the fish solely for this role not only "commoditizes" the fish- it feeds the perception that its sole "purpose" is to "clean the tank." I'll say it one more time:

These small, seemingly non-descript fish are actually quite fascinating and engaging, and worthy of much more attention and respect than merely being regarded as "cleanup crew" by hobbyists.  They are remarkably "social" fish, with interesting interactions and group dynamics that are enjoyable and fascinating to watch.

That is, if we're not adding them to our tanks for the sole purpose of cleaning up "the mess."

Now, I suppose that the popular term "catfish" to the hobby at large over the decades probably instantly brought to mind a picture of a non-descript "bottom-feeding scavenger fish", patiently sifting through the substrate for uneaten food or algae; going about its business as members of it's group had done for eons, blissfully unaware that this was the only shot at sustenance they would get.

Nobody was going out of their way to target feed the "scavengers", right?


Back to the Otocinculus for a bit.

There are about 16 different species of these easily-recognizable (at the genus level, at least!) fish, several of which find there way into the hobby on a regular basis. Telling the individual species apart is challenging at best, so we (unfortunately) sort of lump them together, from a standpoint of needs and care.

Remarkably, when offered for sale in the aquarium trade, many unsuspecting neophyte hobbyists are advised to purchase "one or two" as cheap "algae eaters" for their new tank. And of course, being small, gregarious, social creatures, they can be very shy when kept singly, yet display surpsingly interesting social behaviors when kept in groups of 6 or more.

Interestingly, their dietary preference creates a strange sort of "paradox" for many hobbyists who treat them simply as humble "algae eaters", placed in a tank for the sole purpose of consuming unwanted algal films (which they do an amazing job at, BTW):

They are so good at consuming algae that, in an aquarium without sufficient algal growth, a population of these fishes could literally "eat themselves to death" by consuming all of the available natural food resource rapidly. This is why it's important: 1) not to keep too many in a small tank  and 2) to understand that they can and will consume other foods, like frozen brine shrimp, etc., and 3) to make sure that food is made available to them.

Because of their shy, retiring nature, when you supplement their natural algae diet, you need to make sure that food reaches them, and that the other tank inhabitants don't beat them to the food. It may take a little more time, but these endearing little fishes certainly are worthy of the attention!

It's an extra act of kindness that is most definitely not misspent, in my opinion. Now, "shy and retiring" typically applies to them when they're new. They will often become far more comfortable and be out in the open much more when they've adapted to their new home. And, since they really are found in groups in nature, we feel that keeping a small group of them in the aquarium helps to "socialize" them more quickly.

As stated above, "Otos" are really interesting fishes in and of themselves, and should, in our opinion, be treated like any other fish in the aquarium. That is, you should accommodate their need for food by never adding them to an "immature" aquarium that doesn't have some algal growth present, and making sure that they get their fair share of prepared, aquarist-fed food as well.

And obtaining food is really the main battle these fishes face, and the by-product of poor handling along the chain of custody from capture to aquarist leads to weakened fish with a poor survival record, further reinforcing the negative perception that they are somehow "expendable" creatures...

And as a sort of "confession", I know that for many years, my approach to keeping them was just totally wrong.

These are relatively inexpensive fish, and that often brings about a very cavalier attitude about keeping them. Ironically, they have that reputation of being a bit "touchy", not lasting long periods of time in the aquarium for a lot of hobbyists-suddenly "checking out" for no apparent reason. This unfortunately has given them the undeserved title of a "expendable" fish that you just "replace as needed" (i.e., when the fish "croak")- a horrible moniker for any animal, IMHO. When we look into the way they are handled, their requirements and feeding habits, it become a bit more apparent why they can go so quickly.


First off, from a water standpoint- they are pretty adaptable fish, but being from the Amazon region, they're typically at home in soft, neutral to acidic water. Although the pH and hardness are not super critical, STABILITY is very important to these fish.

Like, this should be the goal for most aquariums containing fishes, but once again, I theorize that, because we've assigned these fish the unfortunate role of "utility players", they're brought in to solve a problem (i.e.; algae) and any specialized needs they might have are viewed as secondary...


Oh, the aquarium. Let's think about that for a second.

I admit, in my less experienced hobby days, I'd unleash a few of these guys in a relatively new, rather unstable aquarium as a "preventative" against algae outbreaks.  I know I used to watch them, convincing myself that they were seemingly continuously "eating" algae (even though I couldn't see it with the naked eye), when the reality was, they were frantically looking for something- anything- to sustain themselves.

I was literally watching my Otos starving to death.  If we're honest with ourselves, we realize that a typical new aquarium seldom has any significant amounts of  algae, right? And if it does, it can be handled by one of two of these guys until it's gone. Yet we (and I include myself in this...) will often add a few as part of the "package" of fishes we consider "necessary" in our new tanks.

Oh, and this brings up yet another problem to the approach we take: These fish are quite gregarious in nature, occurring in large groups with dynamic social structure. The weird sort of paradox here is that it's important to keep them in groups for their well being. They fare far better, and are far more interesting in groups.

Yet, how can you really do this? The problem is, if you don't have enough algae or other food sources available to them on a continuous basis, a group will simply "eat itself to death" faster as the algae are consumed...unless you make an effort to supplement their diet with other foods.

We keep purchasing them for a "role", and nothing more. Or, at least that's the way it's perceived in the hobby.


Our friend Mike Tuccinardi, well-respected author and tropical fish importer, will be the first to tell you that these fishes suffer from that horrible "commoditization" which tends to overtake many small, bottom-dwelling fishes in the hobby. To that end, he suggests that we all consider the challenges the fish face on the way to us, and understand the extra steps that, in a perfect world, should be to assure that they remain healthy before they get to you:

"...it just takes a little TLC along the supply chain to keep these interesting and useful little fish happy and healthy. The primary issue with this fish is access to food – as mentioned earlier they tend to arrive half-starved and weak, which usually traces back to the conditions they were held in immediately after collection.

Sadly, some Otocinclus in the trade may not be fed between that point and the time they reach a store (which can be a week or more), so they are in far from ideal condition on arrival.

They need food. They need a continuous supply of food. They need to be fed directly in systems which don't have sufficient natural food production.

"Okay, really? So now I have to 'target feed' my Otos?" Well, yeah, it makes sense, right? And if you think it's a pain in the ass to do this, you're right. Let's be honest: In an active community tank, have you ever been able to target feed a tiny catfish effectively and regularly, as many authors suggest?

You'll have to spend a fairly significant amount of time trying to deliver foods to these little guys, trying to beat out the more aggressive feeders, all the while hoping that these fish will even show a remote interest unfamiliar foods items, like pellets, zucchini, or spinach, as is often recommended. Flitting over them with active mouths is NOT the same as consuming them.

It's easy to delude ourselves that they are deriving sustenance from these foods sometimes, much in the way we are convinced that they are finding "something" in a new aquarium because they are so "busy." Again, it's not at all impossible- but it requires patience, observation, and a tiny bit of luck...any of which you may not have- or may not want to expend on these fish- if you're honest with yourself.


Gut content analysis of these fishes in the wild shows pretty much two things: algae and the less defined "organic matter" (i.e.; detritus probably bound up in an algal matrix). So, this is a clue that getting them to eat other foods is not gonna be super easy. Not impossible, but certainly not the easiest thing you'll do. And if you take the (unfortunately and widely held)  position that this is a "role playing" fish, destined to be an algae-eating "janitor"- then you really have to be honest with yourself and consider if these fish are for you.

Yet, here is the good news: As we have discussed hundreds of times here, the botanical-style aquarium, when properly set up and operating, provides a near continuous supply of organic detritus, as well as some algal films which are not unusual in this type of aquarium. Perfect for these guys, assuming they're not getting out-competed for it.

Personally, I feel that these fishes should simply not be thought of as "cleanup crews", period.

If you have an algae problem in your aquarium, you need to explore and embrace more advanced nutrient control and export techniques to stop it, as well as the least popular method to control it- manual removal.

We really need to re-think our "relationship" with these little fishes.

Like so many things in our hobby, it involves a "mental shift", a re-alignment of our perceptions, and a greater appreciation for the needs and challenges of the amazing animals that we treasure so much. So please- the next time you're thinking about purchasing one or more of these fishes for the sole purpose of being "algae eaters" in your "high-concept planted aquarium", consider their needs...and if you aren't convinced that this is worthwhile, I'd implore you to consider honing your algae-scraping skills instead, and leaving these little guys to the care of someone who appreciates them for more than just "utility."

Tough love. Yes.

 We have simply not kept these fishes in a "fair" manner for many years, IMHO.


Yeah, they are amazing consumers of algae. I've seen a pair literally strip a 20 gallon tank with modest algae growth completely in 48 hours. And then struggle to survive until the algae returns. Hardly a life for an animal that seems to fare wonderfully in the wild.

I think we lean a bit too much on various animals to perform some of the "roles" that we need to have a better grasp of...This is in stark contrast to setting up an aquarium which accommodates the specific needs of certain fishes or animals. 

This is a pretty common thing in the reef aquarium world, where you see vendors selling packages of snail, crabs, shrimp, and starfishes as "cleanup crews." At first it seems innocent, but beneath the shiny veneer, it's actually kind of dark and sad: We consider these animals a sort of "disposable" and "temporary" commodity- using them for their "cleaning services" until we have no more algae or detritus or uneaten food or whatever in our tanks. Then, if they live, great. IF they perish- well, we can always get more, right?


The "commoditization" of life forms for our tank maintenance...great...

Yep, I see this in the reef aquarium world all the time:  Recommendations for large numbers of animals like Brittle Stars and various snails to handle "detritus"...

One of the big problems I have with some of the more “traditional” detritivorous “cleanup crew” members is that they are often animals that consume detritus as a part of their diet, and make a greater part of their diet the micro and/or macrofauna that you are so carefully trying to cultivate for your biodiveristy and nutrient export processes in your aquarium. They do an excellent job at it, too.


To make matters worse, hobbyists are often advised to keep stupidly large numbers of these animals in their reef aquariums, which assures that not only will they decimate beneficial infauna, but they’ll probably starve to death more rapidly as a result of their own "efficiency."

It's no different in freshwater, really. The "cast of characters" is slightly different, but that's it. The "mission" we've assigned these animals is the same: It's all about eliminating algae and "detritus" in what we consider a "natural" way.

It's the same with snails...

Everyone has their opinions of what animals are best, and how many you should have. “X” number of this-or-that per gallon/liter, or some such nonsense. I think it’s absurd. I mean, really, who has done studies on how much algae an individual snail will consume in Nature? Yet, we as vendors and hobbyists come up with exotic formulae…based on…what, exactly? And how much algae can support “X” number of snails in an aquarium, and for how long? At some point, food supplies will be exhausted with a large population of these animals in residence.

Then what?

I mean, if I were a snail, I wouldn’t want to share my 30-gallon tank with 15 other hungry neighbors. I’d just want the space for myself, or maybe a few friends of the opposite sex. More food, more fun…If you can call a snail’s life “fun”, that is.

We're so worried about algae and detritus that we will do just about anything to rid oursleves of it...including, unfortunately- devaluing animals' lives in the process.

 And we know my position on detritus, right?

I suppose my position sounds harsh, and could possibly be viewed as cynical, or even a bit hypocritical by some.

Yet, without sounding like a judgmental asshole "buzz killer", I think that we should carefully consider the implications and responsibility that goes with these "5 for $10" fishes or cheap snails that we've unfairly assigned the role of "consumable", much like we would a box of carbon or a filter pad.

Sure, It goes against the grain of what we might typically think about when considering these fishes and animals, and brings up some ugly, difficult-to-face truths about our position on the matter, yet it does deserve lots of consideration.


The reality is that every fish which resides in a botanical-style aquarium will forage on stuff like detritus, biofilms, fungal growths, and even algae. Having these in the aquarium is actually a benefit. Few fishes will function as the sole means of "control" of these items.

That's not their "role."

It's ours.

Choices. Responsibility. Morals.

All things that we need to utilize when we think about purchasing this fish- or any other life form which we designate as a "scavenger."

Look, I'm not trying to occupy the moral "high ground", preaching to you that I'm the guy with the answers...I don't pretend to be that person. I find it a tough call, myself. I've killed to many of these fishes over the years needlessly, basking in my ignorance, stubbornness, and denial, and I'm merely telling you how I see it now.

You may have an entirely different viewpoint, capability, situation...Like so many things in the hobby, it boils down making thoughtful, informed decisions. To do what we feel is appropriate and acceptable to us, and in the best interest of the animals that we keep.  A challenging balance. 

So, stay thoughtful. Stay observant. Stay considerate. Stay honest. Stay compassionate...

And Stay Wet.

Scott Fellman

Tannin Aquatics









Scott Fellman
Scott Fellman


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