Wake me up before you "Oto!" Reconsidering the "disposable" Otocinculus catfish...

Okay...here goes...I know I'll get at least some hate mail on this one- with someone ticked off because I appear to be judgmentally "preaching" about something...The disclaimer here is that I am merely giving you my thoughts on a subject which I have personally grappled with before...

One of those things that we as fish keepers seem to have to contend with is that decision between keeping fishes 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.


One of our favorite "little helpers" in the hobby to maintain control of algae in our aquariums is the little Otocinculus catfish from the Amazonian region. 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.

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 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. Another important factor in their survivability is water quality. This means low levels of nitrate, good oxygenation, and a clean, healthy aquarium. 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. 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 them. 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 available on a continuous basis, a group will simply "eat itself to death as the algae are consumed"...unless you make an effort to supplement their diet with other foods.

"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? Really? Because I've done this many times, and it's anything but "easy."  It's pretty much "dump and pray" that they find their treats before everyone else does. And that's a dice roll, at best.

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 an 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.

My position is that, unless you have a large enough aquarium with a significant amount of algae that grows on a near continuous basis, you should consider other means of control, including other animals (such as "Amano Shrimp", which often consume uneaten food and other things in addition to algae), more advanced nutrient control and export techniques, and the least popular method- manual removal of algae. I strongly believe that we have not kept these fishes in a "fair" manner for many years.

It's one of those decisions that we have to make for ourselves. These 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.

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

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

Choices. Responsibility. Morals. All things that we need to utilize when we think about purchasing this fish. 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. You may have an entirely different viewpoint, capability, situation...Like so many things in the hobby, it boils down to what we feel is appropriate and acceptable to us, and in the best interest of the animals that we keep.

So, stay thoughtful. Stay observant. Stay honest.

And Stay Wet.

Scott Fellman

Tannin Aquatics









Scott Fellman
Scott Fellman


1 Response


January 26, 2024

I know this is an old article, but I still wanted to comment.

Your piece on these remarkable little fish (Otocinclus catfish) is genuinely well-crafted and insightful. I wholeheartedly agree with the points you’ve articulated, and I share the sentiment that greater attention should be paid to these invaluable “cleaner” fish; even though it could be a challenging goal, given the competition from other fish that may outcompete them in speed and aggression. It’s disheartening that we extract them from their natural habitats only to neglect their fundamental requirements, subsequently bewailing their fragility. Certain fish species necessitate extra effort on our part to thrive in aquarium settings, and the Otocinclus catfish is undoubtedly one of them. Thank you for your well-written and thoughtful essay on the subject.

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