Otocinclus Catfish Care: Everything You Need To Know

Otocinclus Catfish

Otocinclus Catfish Quick Care Sheet

  • Common Name: Otocinclus Catfish
  • Alternate Common Name(s): Dwarf Armored Catfish, Oto Cat, Dwarf Sucker Catfish
  • Latin Name: Otocinclus vittatus
  • Care Level: Intermediate
  • Tank Size: 5+ Gallons
  • Size: 1 ½” to 2”
  • Diet: Vegetarian/Biofilm
  • Behavior: Peaceful Bottom Dweller, Schools
  • Lifespan: 3-5 years
  • Reproduction Type: Egg Scattering, Very Hard in Captivity
  • Water Temperature: 72° -82°F (22°-28°C)
  • pH: 6.0-7.5
  • Water Hardness: 5–15 dKH

Origins of the Oto Catfish

The Oto Catfish hails from quick-moving streams in South America. They’re spread across large portions of the lowlands east of the Andes Mountains. Their native environment is chock full of plants with high water quality.

They frequent shallow portions of rivers and streams, using their suckermouth to hold in place against the current. Otos are actually armored catfish, having a similar arrangement to plecos with their scales.

Otos are notoriously hard to breed in captivity. That, combined with their dietary requirements, has given them a strange reputation for dying quickly when introduced to aquariums. Most on the market have been wild-caught, often through poisoning. Unfortunately, that means a lot of the Oto catfish sold are already weakened and dying before they go home with an aquarist.

I’ve had a good success rate in the past, roughly 90% of the dozens of Oto cats I’ve had over the years have survived. Decent husbandry is part of it, but a lot of it was simply having a reliable, trusted supplier.

It starts with picking the healthiest fish in the tank, but the key is to have food ready as soon as they get in the tank.

The Otocinclus Catfish is one of the preferred algae cleaners and is usually used with Cherry Red Shrimp in nano tanks to help keep things clean. They’re too small to fit into most community tanks and they’re not going to live long in a tank that doesn’t have plants. Otocinclus Catfish should only be placed in planted tanks.

That said, the tricks in their care are easy to manage for a beginner. 

You just need to be aware of them from the start.

Species Confusion

The most common Oto in the trade is the Otocinclus vittatus but there are a lot of subspecies that sometimes make their way in. On occasion, they’re even mixed with O. vittatus due to their similarity in both looks and size. 

Otos are often sold under the name Macrotocinclus affinis or Otocinclus affinis. It’s generally a misclassification, the true M. affinis seems to be extremely rare in the aquarium trade. 

There are 19 or 20 species in the genus depending on who you ask, with a lot of overlap in their range. Identifying them requires a good handle on fish physiology and a guide to the different species.

To the casual aquarist, the exact species matters little in care. The rest of this guide can still be followed and they’ll be fine.

Selecting Fish

I’d love to tell you to go into the LFS and pick out four or more healthy Otocinclus and call it good.

The truth is that selecting healthy-looking fish isn’t a guarantee that they’re going to survive. The conditions that most have been through, putting them in a bad state when they arrive. It just goes downhill from there since most have no access to biofilm or algae.

That said, you can help your chances a bit if you look for the following:

  • Active- Healthy Oto Cats are active, almost friendly little fish. They’re very social and bold when in large groups. Reserved fish in an active tank may be ill, and a whole tank that seems sedate may have problems.
  • Healthy Belly- The Oto should look neither skinny nor fat. They’ll get nice and fat in your tank, but they won’t look bloated. Bloated fish are most likely sick.
  • Fins and Skin- A quick visual inspection can give you an idea. Fins should be intact, and their skin should have no visible blemishes. Darker coloration is a good sign as well.
  • Eyes- Eyes should be clear with no visible problems. Clouded eyes usually indicate serious health problems.

When you buy a group, some are going to die. If all of them live, consider it a happy surprise! That said, the first couple of weeks are always touch-and-go.

Ideal Tank Setup

Most tropical planted tanks have fine water conditions for Oto Catfish, the devil is in the details with these little, cleaning powerhouses.

If you can manage a planted tank until it’s well-established you won’t have a lot of trouble with keeping them. That said, let’s take a look at the basics so you know what you’ll need going in.

Recommended Setup

You should have the following from the start:

  • Filtration Appropriate for Tank
  • Aquarium Heater
  • Nutritious Substrate
  • Driftwood in Hardscape
  • Plants
  • More Plants

The nice part about these little fish is that they can handle higher volume flow than a lot of nano fish. While you don’t want them in a raging river, they can easily handle 2-3x the recommended flow for your tank’s size, they naturally exist in currents that require them to use their mouths to hold on to rocks.

Driftwood should be the main component of the hardscape. It’s unclear if Oto Cats require rasping like Plecos, but driftwood provides a porous surface that tends to accumulate algae and biofilm. That’s exactly what you want for your Oto.

Heavy planting is a requirement for keeping these fish long-term. Make sure you have your fertilization in order and that your plants are well-established.

More Than Cycling

A newly cycled tank is sufficient for the care of most animals. It will also be for some Otos, but it’s best not to leave it to chance.

Let your planted tank run for 2-4 months, and keep it stable, before you introduce Otos. Otherwise, you run the risk of them starving to death, which is the fate of many of these poor little guys when they’re brought into an LFS.

You need an established tank.

If you’re worried about keeping the tank clean in the meantime, then I’d suggest a hardy invertebrate like Neocaridina davidii to handle detritus and algae buildup in the meantime.

Plant Suggestions

Otocinclus sp. requires a lot of plants. You’re actually looking to increase the surface area of the tank in addition to creating cover and a healthy environment for your fish.

To that end, I suggest leaving them out of landscape-style aquariums that are built around rockwork and carpet plants. Dutch-style rows are great and jungle aquariums are my personal favorite to keep these fish. Most planted tanks that aren’t overly stylized will serve them well as long as everything else is in order.

The following plants are a great choice:

  • Echinodorus sp.The Amazon Sword and many of the species in this genus have broad, dense leaves when they’re established.
  • Cryptocoryne wendtii- Crypts are all great, but C. wendtii is easy to care for and comes in a lot of colors. Just make sure you know about crypt melt going in so you don’t panic.
  • Anubias barteri– Anubias species are great broad leaves for your otos, with the added bonus of being undemanding. Anubias barteri var nana may be a bit small for them, but standard A. barteri and A. hastifolia are both great for this purpose.
  • Microsorum pteropus- Java Fern has long leaves, few care requirements, and can be found in most places that sell fish.

As a personal observation, I’ve noticed Otos seem to prefer hiding under broad-leaved plants to anywhere else. That’s where you should look if you think you have a missing Oto, I’ve found some that have stayed hidden for weeks just chilling underneath a Sword or Crypt.

There are countless more broad-leaved plants that can work well, even some species of Hygrophila. The important thing is to have some broad-leaved plants for your Otos, and as many plants as possible.

You can skip the broadleaves, but your chances of keeping an Oto alive in a tank without plants are very low.

Specialized Care Requirements

Well, let’s stop hinting around about the hardest part of keeping Otos.

Their diet.

Otocinclus Catfish require a mature tank due to their diet being largely biofilm and certain types of algae. Biofilm naturally grows on all of the surfaces in your tank, but in particular on driftwood and plants.

Without it, the majority of these fish will starve. Many people just assume they’ll clean the tank and maybe drop in an occasional algae wafer. In my experience, most Otos won’t know what to do with a wafer so their health relies largely on their environment.

The reason so many people have trouble keeping Oto Cats alive is… well, the whole commercial chain. Your average Otocinclus vittatus goes through the following:

  1. Poisoning- Poisons are often used to dull or stun the Otos in the stream they inhabit. A good chunk of them will die here, before even being packaged.
  2. Shipping- If not properly packaged, shipping can kill more of them before they arrive. Even with proper packaging, this is another 2-3 days of starvation for the fish. The fish are shipped in groups, and any diseases they suffer can spread.
  3. The Store- I’ve seen Otos kept in a tank where they had food readily available once. The majority of them end up in standard sales tanks, which may have a few plants tossed in at best. They will continue to starve in these conditions.

So you have a fish that’s been poisoned, starved, and shipped a full continent away from home (if you live in the US, Europe and Japan are even farther). These fish are wild-caught, so diseases are an issue as well.

Some raise ethical questions about keeping Otos. The answers to them are more complicated than a simple care sheet can answer. I can only say that the industry can always show improvement and Otocinclus Catfishes aren’t unique in this regard, it’s just that their dietary requirements lead to a higher death rate than we see in most wild-caught fish.

The key to a long-lived Otocinclus Catfish is to put them in a mature tank. Unfortunately, the damage is sometimes done and these fish can die even when introduced to a tank with plentiful food. 

The majority, however, will quickly acclimate once they’ve been fed. Just wait a bit before you put them in a recently put-together tank, you’ll have much better results.

Suitable Tankmates

Unlike Pleco, Oto Cats are suitable with most fish that won’t harass or eat them. The latter tend to get large and unruly as time goes on. Otocinclus Catfish, on the other hand, are one of the most peaceful fish around.

The first thing to remember is to always keep your Oto Cats in groups of 4+. These fish are quite social and enjoy the company of their own species. I’ve found they tend to be bolder and more active as the school size gets larger.

They’ll spend most of their time on the bottom of the tank. They seem to mix well with Corydoras sp. but I recommend not keeping them with any other catfish. The majority of them will eat an Oto if they’re given a chance.

Otos shine as cleaners for smaller tanks with display fish. Some of the suitable tankmates in a nano tank are:

  • Betta Otos and Betta get along well. They won’t interact much, if at all, thanks to their difference in preferred swimming height. Particularly aggressive Betta may harass Oto Cats minimally.
  • Galaxy Rasbora/Celestial Pearl Danio Tiny, schooling top swimmers mixed with tiny bottom dwellers? These are a very good match for the most part.
  • Chili Rasbora- Chili Rasbora fit the bill well, they’re even smaller than the Otos! Like the above, there will be minimal interaction.
  • Endler’s Livebearer- Otos do well with Endler’s, especially if you want to breed them.

I’ve personally kept all of the above with Otocinclus Catfish, and they do well.

One of the big selling points of Oto Cats is the fact that they don’t eat the fry. I can’t think of another fish off the top of my head that will refuse to eat any kind of fry, including baby shrimp. For the rest? Babies are free meals if they can fit in their mouths.

Thus, the only thing you need to worry about when choosing tank mates is whether or not they’re going to eat your Otos. Don’t place Otos with known aggressive fish even if they’re not big enough to eat them. Otos don’t fight back, so you’re not going to reach any kind of balanced aggression equilibrium.

Shrimp Breeding Tanks

For those who breed micro shrimp species, such as Cherry Red Shrimp or Bee Shrimp, the Oto has a special place: they don’t eat shrimp fry.

If you don’t breed shrimp, this may seem like an unremarkable quality. If you do like to have an increasing shrimp population, then you have a fish that can co-exist with them.

I use Otos in any planted tank under 20 gallons, and I often like to have a thriving shrimp population as well. Cherry Red Shrimp and Otos are an excellent combination, once the shrimp have reached a sizable population you can add other fish.

Breeding Otocinclus Catfish

Let’s be upfront: there is no established way to breed Otocinclus Catfish in an aquarium. If you’re looking for a step-by-step guide… there isn’t one.

There are also rumors about secret South American breeding operations, which may or may not be true. It would explain how these fish end up being so cheap through the whole year, but I’ve been unable to find a definitive lead.

I’m personally wary of anyone offering tank-raised Otocinclus Catfish. Even when bred successfully there have been some major problems rearing fry.

There are a lot of rumors and hearsay around the whole matter. However, it’s been done successfully by some aquarists who’ve made available the little bit of data we have.

Triggering Breeding

Most people who’ve had their Otos breed note that they’ve done two things:

  • Fed a high protein diet consisting of daphnia or baby brine shrimp
  • Made a large (40-60%) water change

Everything else seems to be pretty variable. For the most part, we’re not even sure if they’re seasonal yet.

Every tank that I read about being a success was heavily planted as well.

Known Breeding Behavior

The breeding behavior of these little guys is similar to Corydoras sp. They form a T-position and then scatter eggs across the tank. 

Most reports show the fry as being free-swimming within a day of the eggs being laid. That could be due to only noticing the behavior later on in the cycle, however.

They do not appear protective or aggressive with their offspring.

The fry, once swimming, are very tiny and it may be hard to find them in the densely planted tank that Otos prefer. Some sort of magnification is a good idea if you’re hoping to spot them quickly.

Feeding Otocinclus Catfish Fry

It appears that the fry is too small to eat the usual suspects when they’re firstborn. They can often be seen grazing, but it’s unknown if that’s their sole food source.

Infusoria, or green water, is the best way to get them fed. The fry are too small to even feed on daphnia in many cases. I recommend cultivating a jar if you’re hoping to breed these fish.

Recently, some of those who’ve had success rearing fry have suggested micro worms as a possible food source. Information about full setups is scant, but a lot can be gleaned from online posts and even interviews with people who’ve successfully bred Otos.

Success with breeding and raising these fish is very rare, so seek out every bit of information you can if you decide it’s a project worthy of your time.

Small Mouth, Big Impact!

Otos are a mainstay for those of us who keep planted aquaria. Their unique behavior and habit of cleaning up the tank are fun and useful. Once these fish are established in an aquarium you’ll forget how fragile they’re reputed to be.

Just make sure you know how to keep them fed!