Otocinclus 101: Size, Care, Tank Size, Breeding & More!

If you’d love a catfish for your tank but don’t know which one to get, the Otocinclus is a fantastic option. These guys are unfussy and can tolerate a wide range of water conditions. This means you won’t lose hair trying to get their water just right. As a matter of fact, they’re unbelievably low-maintenance. They’re tiny, friendly, and diligent little catfish who even help in tank cleaning! 

The table below gives a quick overview of the Otocinclus catfish profile:

Profile AttributeValue
Care DifficultyEasy 
Lifespan3-5 years
Color(s)Brown, gray, green (depending on species)
Maximum Size2 inches
Minimum Tank Size10-20 gallons
Tank SetupHeavily planted/sand substrate
CompatibilityPeaceful community tanks

Below is our Otocinclus catfish care guide, continue reading to know more about its tank mates, diet, lifespan and more.

Otocinclus catfish Overview

To get all technical, the name Otocinclus is actually not a specific fish but a genus of catfishes. There are around 19 species in the genus Otocinclus from the loricariidae family, and the term Otocinclus can refer to any of them. These tiny catfishes are also known as Otos, Oto cats, Midget sucker fish and Dwarf suckers. Otocinclus catfish are native to South America, but uniquely do not come from the Amazon river. 

Oto cats are herbivorous fishes that have a variety of appearances, depending on their species. They’re bottom-dwellers who are good-natured and keep to themselves. Otos aren’t just decorative either; they are also heavy-duty tank cleaners. To be more exact, these fishes are herbivores who love algae more than anything. They scour through the tank and upon spotting algae overgrowth, start nibbling. Otos aren’t too strict with their requirements, and they don’t need a lot of space, which is good news for hobbyists out there. For those on a tight budget, Oto cats are also thankfully quite affordable, cementing their popularity among newbie fishkeepers.


Otocinclus catfishes comprise many different species. As such, their patterns and colors can vary from one to the other. However, Otocinclus species share a few general characteristics. The Otocinclus catfish is a nano fish with a shark-like or cigar-shaped body. Their bodies taper towards the head and tail ends, and they have strong mouths often referred to as a ‘sucker-mouth’. From the name itself, their mouths can stick to surfaces and suck any algae that may be present; cleaning said surface in the process. These catfishes also have armor plating in their bodies, that most other catfish genera don’t possess. These plates  serve as an extra layer of protection against damage. While the colors range from brown, green to gray, many Oto cats have a dark streak running along their sides. Here are some of the more common Oto species in the hobby:

Common Otocinclus (Otocinclus vittatus)

From its name itself, the common Oto is the most prevalent of the genus. They can be found all over South America, and they have a murky brown and white color. These guys have a speckled light brown pattern above their dark lateral streak.

Zebra Otocinclus (Otocinclus Cocama)

The Zebra Oto is one of the more striking Oto cats in the genus. It has stark black and white stripes all over its body, hence its name ‘zebra’. A couple of horizontal stripes are present on its head, which soon transition into vertical stripes. These Otos are also sometimes called Tiger Otos, when its stripes are slightly wavy. Zebra Otos are also some of the pricier Otocinclus cats in the market, capable of putting a dent in your wallet. 

Golden Otocinclus (Otocinclus affinis)

Golden Otos are very similar to the common species. While not truly golden, their patterns are less brown than the common Oto and appear closer to yellow ochre. 

Average Size

Oto cats are categorized as nano fish. They’re immensely tiny, with an average length among species of only 1-2 inches. Species like the Otocinclus tapirape for example, can only grow to a measly one inch. While some species end up exceeding the expected 2 inches, the difference isn’t very significant. 


Unfortunately, Oto cats only have a life expectancy of around 3-5 years. This seems like a short time, but don’t be disheartened. Proper care and maintenance of their water quality can go a long way for these tiny algae-eating machines. 

Tip: Many distraught owners find that their Otos die within a couple of weeks of purchasing them. Sadly, this is primarily because they were severely underfed in pet shops. To avoid this, get Otos with full bellies when buying so you can be sure they are in good health.

Otocinclus catfish Care

Many owners find the Oto cats as solutions to their tank algae problems. Instead of scrubbing off the algal growths with a toothbrush, many find that there is almost nothing more efficient in cleaning up than the Otocinclus catfish. 

Keeping an Oto cat is not as challenging as people might make you believe either. They’re small and even-tempered so tank size and mates are non issues; they’re unfussy eaters, and they clean tank walls and ornaments! It’s almost all positive, really. The only thing you have to do for them in exchange is keep their waters clean, and give them some well-deserved company. 

Tank Size

They may be tiny, but Oto cats are shoaling fish. They need members of their own kind to truly thrive in a tank. You need to house at least 6 otos in your tank so they would be happy and more outgoing. A tank size of around 10 gallons minimum should accommodate around 6 Oto cats. Of course, a bigger tank of around 20 gallons would be better for these catfishes. Remember to always give allowances for your ornaments, and other fishes (if you’re planning on a community tank). 

Water Parameters

More than a specific pH, temperature or hardness, Otos need clean water the most. They can withstand a wide range of water conditions, but filthy water can most definitely be fatal for them. They need well-oxygenated water with practically no ammonia, nitrites and extremely low nitrates (less than 20 ppm). Because of their ‘clean water’ requirements, some don’t recommend Otos for complete beginners. It is more recommended for those with at least some experience in maintaining water quality.

Water Parameters: 

  • Temperature: 70°F-82°F
  • pH levels: 6.0-7.5
  • Water hardness: 6-15 dH
  • Water flow: mild to moderate

To keep Oto’s water perpetually clean, perform weekly 30% water changes regularly. Set up a strong, high-quality filter that has a GPH rating four times the volume of your aquarium as well. This filter is essential in keeping your waters clean, and providing some water flow in the tank. Consistency is key for Otos, since they’re pretty sensitive to unstable water parameters. Make sure to clean up any leftover veggies you might feed your Otos, so they don’t rot in the tank.

Typical Diseases

Fortunately, Otos aren’t any more sickly than the next freshwater fish. There aren’t any species-specific diseases for you to lose sleep over either. However, this doesn’t mean your little friends will never get sick. Oto cats can succumb to the common culprits such as Ich, fin rot, fungal infections, dropsy, and the most prevalent-malnutrition. 

Most of these ailments are highly preventable, as long as you pay attention. One of the best ways to prevent sickness is to keep their water clean, therefore making them happy. Remember that stressed Otos are sickly Otos, and will most likely get ill as a result. Feed them well-balanced and regular diets such as algae wafers or nutritious pellets as well, to prevent malnutrition. 

Tank Setup

Aquascaping with Otocinclus in mind isn’t really common among fishkeepers. In fact, most owners already have built freshwater aquarium ecosystems in place before adding Otocinclus for their cleaning capabilities. Apart from their water requirements, these fish are absolutely easy to please in the tank. They’re very simple fish with very simple needs. Otos are algae-eaters, so they usually stick to areas where algae might propagate. Since algae naturally grows on plant surfaces, they need a heavily-planted tank. Don’t think twice and go crazy with vegetation (as long as it fits in your tank). Some marvelous plant choices are: Anubias, Echinodorus, Java fern, Java moss, and Cabomba. 

When they’re not scouring the aquarium for food, they can also be seen hanging out on smooth stones and bogwood. Placing a couple of cave-like structures in your tank can also be a good idea. As you decorate, make sure your ornaments don’t have any sharp edges that can injure your Oto. Harsh or coarse substrates can also damage your catfishes so it’s best to opt for more soft sand substrates.

In terms of cleanliness, it’s important your aquarium has a high-quality, heavy duty filter (canister) to keep waters pristine. Having test kits on hand is also useful, since you’ll be monitoring your  tank’s ammonia, nitrite and nitrate levels every so often.

Food & Diet

Many aspects of the Otocinclus are decided by its obsession with algae. These tiny catfishes are huge algae-eaters, who eat them well until adulthood. They love their veggies so much that in the wild, Otos spend the majority of their time grazing diatom algae that forms on the surface of aquatic plants. Their habit of spending time in shallow waters is also influenced by their love for algae. To be more specific, more light reaches shallow areas, thereby increasing the amount of algal growth; and where there’s algae, there too is the Oto cat. 

Otos will eat soft green algae and brown diatom algae.

People just let them eat algae and don’t bother feeding them because they think the Oto is eating algae around the tank anyway. Most tanks cannot produce enough algae for Otos however, causing Otocinclus catfish to be underfed. Don’t rely on your tank’s algae to fully sustain your Otos. Give them regular meals and don’t depend on your tank algae. 

Preferred Food for Otocinclus includes:

  • Algae wafers
  • Lettuce
  • Spinach
  • Zucchini
Tip: Take a look at their bellies. A slightly sunken belly is a bad sign. Their bellies must be rounded or full-looking, otherwise, it means your Otos are not getting enough food in their daily lives. Keep your Otos fat, and therefore, happy.

Mating & Breeding Behavior

It’s hard to say whether the Oto is sexually dimorphic or not, as differences between the sexes are very slight. Females are said to have more of a full-looking abdomen when viewed from above, but this can be hard to distinguish from a male Oto who just had his meal. 

In fact, breeding them in aquariums can prove to be a bit of a challenge. It’s not impossible however, as many fishkeepers have successfully bred these catfishes. So far, there are no known specific triggers to induce mating in Otocinclus.  Oto mating and breeding is very similar to Cory catfishes. The male Oto runs around annoying the female, whereby they sort of intertwine with one another. The mating pair is known to kind of ‘sniff’ each other during their dance, and later the male fertilizes her eggs. Female Otos are egg-scatterers, and I do mean scatter. Their eggs spread out all over the tank, the leaves, ornaments, you name it. Take a close look at the eggs once they’re scattered. Bad eggs have a cloudy white quality to them, whereas good eggs are clear and see-through. These bad eggs are cloudy or fuzzy because of a fungus, so it’s best to take them out of the tank immediately. 

Daddy Otos will do the natural thing afterwards, which is to guard and defend his little unhatched offspring. The eggs take a couple of days to hatch into fry, during which the dad still guards them strictly. If you want to avoid any unwanted battles, you should  separate your Otos from other tank mates during breeding. 

Otocinclus Tank Mates

Otocinclus are born to be social. They not only love being part of shoals, they’re also capable of being friends with other fish in the wild. Otos are small and sometimes timid however, so placing them with large or aggressive fish is a definite no. Avoid putting them together with slow and deep-bodied fish like Discus and Angelfish; Cichlids and Oscars are also a risky tank mate to have. These fish can end up chasing your Oto around and killing them in the blink of an eye. Despite these bad choices however, you’re still left with a multitude of potential tank mates.

Suitable Tank Mates for Otocinclus:

  • Corydoras
  • Rasboras (small ones)
  • Peaceful Tetras 
  • Mollies
  • Danios
  • Cherry barbs
  • Guppies
  • Amano or Cherry shrimps
  • Snails

Otocinclus Temperament & Behavior 

For anyone who’s ever owned an Oto, you would know that it’s impossible not to love them. These diurnal catfishes have a truckload of personality, as any fishkeeper would tell you. They’re peaceful and don’t have a mean bone in their bodies. They also become more comfortable and outgoing when kept in a large shoal (10-15). In fact, back in the wild, Otos can be found swimming alongside thousands of other fish. In your community tank, of course, you can’t fit a thousand fishes. Settle for a school of at least 6 Oto cats instead to keep them happy and comfortable. 

Majority of an Otocinclus’ time is spent at the bottom, or resting upon bogwood or leaves. Sometimes you also chance upon them sticking to your tank walls, giving you a glimpse of their cute bellies. When they do this, it’s usually because they’re on the hunt for algae. Once they realize there is no algae to be devoured however, they will try their luck elsewhere.

While Oto cats are generally even-tempered and sometimes even shy, there are few reports of them sticking to deep-bodied fishes. It’s unclear why they do this, but the belief is that they hope to feed off the slime on other fishes’ backs. This attachment to other fishes’ can end in disaster, as the bigger fish will usually get mad (understandably) and attack your Oto. 

To End

All things considered, Otocinclus catfish are great additions to any community tank. They’re unproblematic tank mates, small, and pleasing to the eyes. To top that all off, they even help keep your community aquarium spick and span! Apart from their (semi) fussy water requirements, these guys are low-maintenance, affordable, and perfect for all types of hobbyists. 

Note: Please consider the environment before printing this Otocinclus care sheet.

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