How Many Otocinclus in a 20 Gallon Tank Should You Have? - "Otocinclus Catfish on Java Fern Leaf" by aquaticmag is licensed under CC BY-SA 2.0.
How Many Otocinclus in a 20 Gallon Tank Should You Have? - "Otocinclus Catfish on Java Fern Leaf" by aquaticmag is licensed under CC BY-SA 2.0.

Appearance and Behavior

Otocinclus, commonly known as Otos or Otocinclus catfish, are small freshwater fish that are popular choices for aquariums, especially in community tanks. They belong to the Loricariidae family and are native to South America, mainly found in the Amazon River basin.


Otocinclus are small fish, usually reaching a maximum size of around 1.5 to 2.5 inches (3.8 to 6.4 cm) in length. Their body is elongated and has a somewhat flattened shape. The coloration of Otos can vary, but they typically have a base color of light to dark brown, sometimes with a greenish tint. They also have a distinct black stripe running along their body, from the snout to the tail.


In an aquarium, Otocinclus are peaceful and social fish that prefer to be kept in small groups of 3 to 6 individuals. They are primarily bottom-dwellers, and you’ll often find them grazing on algae that grow on various surfaces, such as rocks, plants, and even the glass walls of the aquarium. Due to their algae-eating behavior, they are often sought after for their usefulness in controlling algae growth in the tank.

Otocinclus are generally not aggressive towards other fish and spend most of their time in the lower levels of the aquarium. They are quite active during the day, and their movements are relatively quick and agile, which can be entertaining to watch.

Since they are a bit sensitive to water conditions, it’s essential to provide them with a well-maintained and stable environment. Otos thrive in aquariums with plenty of plants and hiding spots, as they can be a bit shy and may require places to retreat when feeling stressed. They prefer soft, slightly acidic water with a pH range of around 6.5 to 7.5 and a temperature range of 72 to 79°F (22 to 26°C).


So, what does Otocinclus eat? As mentioned earlier, Otocinclus are algae eaters, and in a well-established aquarium, they can often find enough algae to sustain themselves. However, in some cases, especially in newer setups or if the algae growth is insufficient, you may need to supplement their diet. You can provide them with algae wafers, blanched vegetables (such as zucchini or cucumber), or specialized sinking pellets designed for herbivorous fish. Be careful not to overfeed them, as uneaten food can lead to water quality issues.

So, Otocinclus are peaceful, algae-eating fish that can be a great addition to a community aquarium. Taking care of their specific habitat needs will ensure they remain healthy and active, helping to keep your aquarium clean and free of excessive algae.

So, How Many Otocinclus in a 20 Gallon Tank Should You Have?

How many Otocinclus in a 20 gallon tank should you have? In a 20-gallon tank, the number of Otocinclus catfish you can keep depends on several factors, including their adult size, the presence of other fish in the tank, and the overall aquarium conditions.

As mentioned earlier, Otocinclus are small fish that typically reach a size of around 1.5 to 2.5 inches (3.8 to 6.4 cm). They are social creatures and prefer to be kept in groups of at least 3 to 6 individuals. Keeping them in a group provides a more natural and comfortable environment for them, and it helps to reduce stress.

Considering their small size and low bioload (amount of waste they produce), a 20-gallon tank can accommodate a small group of Otocinclus. However, it’s important to take into account the other inhabitants of the tank. If you have a relatively low number of other fish that are also small and have a minimal bioload, you can keep a slightly larger group of Otos. On the other hand, if you have a more heavily stocked tank with larger or more fish that produce more waste, you may consider keeping a smaller group of Otocinclus.

As a general guideline, a 20-gallon tank can comfortably house around 4 to 6 Otocinclus catfish along with other compatible tank mates. Just be sure to provide them with enough hiding spots, plants, and algae (or suitable alternative food) to keep them happy and healthy. Also, always ensure good water quality and conduct regular maintenance to create a thriving environment for all the inhabitants in the tank.

How Many Otocinclus in a 20 Gallon Tank Should You Have? - "Otocinclus Catfish on Java Fern Leaf" by aquaticmag is licensed under CC BY-SA 2.0.
How Many Otocinclus in a 20 Gallon Tank Should You Have? – “Otocinclus Catfish on Java Fern Leaf” by aquaticmag is licensed under CC BY-SA 2.0.

Tank Setup

Creating a well-decorated 20-gallon community tank for Otocinclus and their tank mates involves providing suitable hiding spots, plant life, and maintaining a balanced environment. Here are some guidelines on how to decorate the tank:

  • Substrate: Use a fine-grained substrate like sand or smooth gravel. Avoid using sharp gravel or coarse substrates that might harm the sensitive barbels of the Otocinclus.
  • Plants: Include plenty of live or artificial plants in the aquarium. Otocinclus appreciate dense plantings as they mimic their natural habitat. Plants also offer additional surfaces for algae growth, which is an essential part of the Otocinclus diet.
  • Driftwood and Rocks: Incorporate some driftwood and rocks in the aquarium to create hiding spots and shelter for the fish. These natural elements not only provide hiding places but also create a visually appealing environment.
  • Caves and Tubes: Use PVC pipes or aquarium-safe caves to offer additional hiding spots for the Otocinclus and other tank mates. Providing multiple hiding spots helps reduce stress and territorial disputes among fish.
  • Algae Growth: Allow some algae to grow naturally in the tank. Otocinclus are algae eaters, and this will provide them with a supplemental food source. However, if algae growth is insufficient, you can provide specialized sinking algae wafers or pellets as a supplement.
  • Lighting: Opt for moderate lighting to support plant growth and encourage algae development. Too much light can lead to excessive algae growth, so it’s essential to find the right balance.
  • Tank Mates: When choosing tank mates for Otocinclus, consider peaceful fish that won’t compete for resources or harass the Otos. Good tank mate options include small schooling fish like tetras (e.g., neon tetras, glowlight tetras), small rasboras, and peaceful livebearers like platies or guppies. Avoid aggressive or fin-nipping fish as they can stress the Otocinclus.
  • Water Parameters: Maintain stable and suitable water conditions for the chosen fish species. Otocinclus prefer slightly acidic to neutral pH (around 6.5 to 7.5) and a temperature range of 72 to 79°F (22 to 26°C).
  • Filtration: Use a proper filtration system to keep the water clean and maintain good water quality. Otocinclus are sensitive to water parameters, so regular maintenance is essential.
  • Fish Density: Consider the adult size and behavior of the fish you choose and ensure the tank doesn’t become overcrowded. Aim for a balanced and harmonious community with enough space for each species. This is also part of the considerations when talking about how many Otocinclus in a 20 gallon tank that you can have.

By providing a well-planted and decorated 20-gallon tank with suitable tank mates, you can create a natural and enriching environment for Otocinclus and their companions, promoting their well-being and overall health.


In conclusion, creating a well-decorated 20-gallon community tank for Otocinclus and their tank mates, and considering the question, “how many Otocinclus in a 20 gallon tank can I have?”, involves thoughtful planning and attention to the needs of the fish. Providing live plants, driftwood, rocks, and hiding spots not only enhances the visual appeal of the aquarium but also mimics their natural habitat, reducing stress and promoting a healthier environment. Selecting peaceful tank mates and maintaining suitable water parameters are crucial for fostering a harmonious community. By ensuring proper care and a balanced ecosystem, the aquarium becomes a thriving and enjoyable home for the Otocinclus and their companions.