Otocinclus catfish are peaceful little algae eating fish that thrive in planted aquariums. These fish are easy to care for, active, and help keep your fish tank clean. Here’s everything you need to know about Otocinclus so that they can live long and healthy lives.

Otocinclus Catfish Video

Oto Catfish Images

Other Names

  • Oto
  • Oto Cat
  • Dwarf Sucking Catfish
  • Midget Sucker Fish

Otocinclus In The Wild

Otocinclus are a type of catfish that are native to South America. Oto Cats like to be in big schools and live in slow-flowing waterways. They are most active during the daytime. These fish have sucker-like mouths that they use to cling to surfaces. They use their suckers to feed on algae found on roots, leaves, stones, etc.

Oto Catfish In Aquariums

Once tank conditions are ideal, you will see Oto fish swimming about in search of food during the day. They suck on fish tank decorations, plants, the glass, anything that has algae.

Otos can also breathe air. So, they sometimes come to the surface of the aquarium for a breath. If you Oto does this, check that your aquarium water has enough oxygen (there are tools to do so).

Otocinclus Catfish Size

Otocinclus are small fish (nano fish). They grow to between 1/2 to 2 inches at maturity. Due to the Otocinclus Catfish’s small size, they are fast and dash around the tank in search of food.

Tank Mates For Otocinclus Catifsh

Otocinclus can live in a tank with other peaceful fish. Never add aggressive fish or other algae eaters that can compete for food. Here are some decent otocinclus tank mates:

Avoid keeping the following fish in the same tank as Oto catfish:

How To Set Up Otocinclus Tank

Most species of Otocinclus live in the same water conditions. They need clean and clear water to thrive. So, aim for an aquarium filter that can cycle water four times an hour.

Ensure that nitrate levels stay between 0-20ppm and that there’s no trace of ammonia and nitrite.
Otos like a stable pH level, so aim for a neutral to a minor acidic pH (6-7.5) to keep them happy.

Otocinclus is a tropical fish, so keep the water temperature between 72-82°F (22-28°C). Use a water heater to keep the temperature stable. Add lots of live plants to your aquarium and do a weekly 25-30% water change to help keep the water clean.

Tank Size

Oto catfish live in shoals or schools. These schools comprise thousands of Otos in the wild. So, keep 10-15 Otos in a tank—the bigger the aquarium, the better. You also have to consider the other fish in the tank: the more space, the better.

If your tank is not big enough to house that number, then add no less than 6 Oto fish. To keep 10-15 Otocinclus fish, you need a 20-gallon tank. For 6 Otos, you can use a 10-gallon aquarium.

Preferred Water Conditions

  • Filter with a GPH rating 4x the volume of your tank
  • Nitrates between 0-20ppm
  • No ammonia or nitrite in the water
  • Water Temperature: 72-82°F (22-28°C)
  • pH: 6-7.5
  • Water Hardness: 6° to 15° DH


Water quality is of utmost importance. So, get a canister filter that has a GPH rating of 4x the volume of your tank.
Otos need oxygenated water. So, water circulation and aeration are essential. You can use an air pump/water pump to help with oxygen levels and water circulation.

Use LED lights to help your plants grow. But, remember to turn them off at night because fish do need sleep.
Go to an online fish store to buy test kits to keep track of the ammonia, nitrite, and nitrate levels in your fish tank.

Fish Tank Plants

Otos feed on algae that grow on plants. The following slow-growing plants are best:

  • Anubius
  • Cabomba (try to get this one)
  • Cryptocorynes
  • Echinodorus
  • Java Fern
  • Java Moss

How To Feed Oto Catfish

Oto catfish are always feeding on soft green algae. But, well-kept aquariums don’t produce enough algae for Otos to eat. So, you need to supplement their diet with algae wafers, vegetables, or catfish pellets.

Vegetables Otos can eat:

  • Brussel Sprouts
  • Romaine Lettuce
  • Spinach
  • Zucchini (Courgette)

You need to make sure that vegetables sink to the bottom of the tank. To do so, use a veggie-clip or tie veggies to a small rock using a string. Never leave vegetables in an aquarium for more than three days. And, always wash your vegetables to remove pesticides.

How To Breed Oto Catfish

Female Oto fish are a bit bigger and broader than male Oto fish. Other than that, there’s not much in the way of telling them apart. Otocinclus don’t usually breed in aquariums, but it can happen.

  • When mating, females swim up and down the tanks while the males chase them.
  • When they are ready to mate, the Oto fish get into a ‘T’ like position.
  • The female Oto fish releases and holds the eggs with her ventral fins.
  • Once she finds a surface to put the eggs, the male Oto fish then fertilizes them.

How To Add Oto Catfish To A New Tank

Quarantine your Oto fish for about 2 weeks to make sure that they are healthy. Then, introduce Otos to a well-cycled fish tank that has no ammonia or nitrates. Nitrates should be below 20ppm.

It’s best that there is some algae growth in the aquarium so that the Otos can start scavenging for food. You can use an acclimation kit or the drip method to add them to a new tank. See the references below for more information.