Otocinclus Catfish: Caring for Your Aquatic Helpers

Otocinclus (lat. Macrotocinclus affinis) is a small and not bright catfish – however, it’s one of the most efficient algae eaters in a tank. That catfish together with Amano shrimp are able to keep you tank and all plants in it clean and tidy.

Habitat in the wild

The Otocinclus catfish, commonly known as the “dwarf suckermouth catfish,” belong to the family Loricariidae. Loricariidae is a diverse family of catfish that includes numerous species with different sizes, shapes, and characteristics.

Nowadays otocinclus catfishes numbers about 16 or 17 different kinds, which are sold in pet shops like one species. Macrotocinclus affinis and Otocinclus cocama (zebra oto) are more commonly seen. Despite the fact that high percentage of otocinclus on the market is represented by Macrotocinclus affinis or other species falsely considered to be Macrotocinclus sp.

They are spread from Colombia to North Argentina. The otocinclus catfish used to be found in the Andes Eastern part. One catfish species has rather restricted habitat in Peru, Brazil and Paraguay, while the other its species can be seen everywhere along the Amazon and Orinoco river basin headwaters.

Dwarf sucking catfish mainly inhabits in small or middle-sized rivers with moderate flow. Usually you may encounter this fish in streamside vegetation, especially in the grass among the water plants with large number of small leaves. You may also see this catfish in some open water mass. There otocinclus catfish swims in shoals above sandy bottom areas filled with tree roots.

Their natural habitat is characterized by densely vegetated areas with plenty of submerged and overhanging plants. Otocinclus catfish are often found in areas with a lot of aquatic vegetation, as they feed on algae and biofilm that grow on the surfaces of plants and other objects.

These catfish prefer clear, oxygen-rich waters with minimal currents. They are well-adapted to environments with low light levels and are usually more active during dawn and dusk. In the wild, they live in large groups, forming schools to help protect themselves from predators.



Otocinclus catfish body is elongated and flattened from sides covered with wide bone scales (the whole body, except the abdomen). The fish has large eyes; its mouth is cupule-shaped. Due to its intestinal respiration catfish can breathe with outer air. Body coloring has some yellowish tint and there is a wide black-brown stripe along the body. The fins are transparent and colorless with some greenish tint.


Female is fatter and larger than the male. Otocinclus catfish size may be up to 4 cm (1.6 in) in length when kept in aquariums. However, their size can vary slightly depending on the species and their individual growth rates.

Their small size makes them popular choices for community aquariums, especially for aquarists who have smaller tanks or prefer to keep smaller fish species. Due to their diminutive size, they are well-suited for nano aquariums or planted tanks where they can help control algae growth and contribute to the overall aesthetics of the tank.


The lifespan of Otocinclus typically ranges from 2 to 5 years when kept in well-maintained aquariums. However, with proper care and a suitable environment, some individuals have been known to live beyond 5 years. The lifespan of any aquarium fish can be influenced by various factors, including water quality, diet, tank size, and the overall health and genetics of the fish.

Scientific NameOtocinclus spp. (Several species in the genus)
Common NamesOtocinclus catfish, Oto, Dwarf suckermouth catfish
OriginSouth America, primarily in the Amazon River basin
SizeUsually 1.65 inches (4 centimeters)
Lifespan2 to 5 years or more in well-maintained aquariums
BehaviorPeaceful and social, prefers to live in groups
DietHerbivorous – feeds on algae and biofilm
Tank SizeMinimum of 10 gallons for a small group
Water ParametersTemperature: 72°F to 78°F (22°C to 26°C)
pH: 6.5 to 7.5
Hardness: 2 to 15 dGH (soft to moderately hard water)
Tank SetupPlanted aquarium with hiding spots and driftwood
CompatibilityPeaceful and suitable for community tanks with non-aggressive fish
BreedingChallenging in captivity and usually occurs in large aquariums
Special ConsiderationsSensitive to water quality, avoid sharp substrates

Difficulties in keeping

Despite its small size Macrotocinclus affinis is quite a demanding in care fish. It requires ideally clean water with stable parameters. Therefore, it’s not recommended for the beginners. However, oto catfish is second to none among any other fishes as for efficient tank cleaning from algae.

The fish does it all day long – it looks for algae and it doesn’t harm even the smallest and the most tender tank plant leaves, such as Hemianthus callitrichoides Cuba, Glossostigma elatinoides and even Java moss.

Care and keeping in a tank

Tank size

It’s better to keep in groups of 5-10 species. Takashi Amano advises to have 100 liters of tank capacity (26,42 gallons) for about 20 fish when starting Nature Aquarium and about 2-3 otocinclus catfish species after the ecosystem settles down. If the tank isn’t that thickly planted, then 10 species for 100 liters of tank capacity (26,42 gallons) is enough. In case of 30 liters capacity tank (7,93 gallons) 4 catfish will do just fine.

Water parameters

Care is the same for all Otocinclus species. It’s partly caused by the small size and its intolerability to polluted and dirty water. The latter is the main reason of the good health and fast growth in tanks with low plants density and perfect quality of tank water.

You’ll need some strong water filters capable to renew the whole amount of tank water at least 3 times in an hour. Such filters have to insure absence of ammonia or nitrites and decrease the amount of nitrates up to 0-20 ppm. For constant renew of a tank system and to keep comfortable tank conditions it’s necessary to renew about 25-30% of the tank water every week.

Chemical composition of the tank water isn’t very important, the main thing is that the water should be clean and fresh water, the temperature should be 21–27 °C (70–81 °F), and pH balance of the water has to be neutral or slightly acidic.

Once you create such tank conditions and your fish will feel itself at home. In the wild otocinclus catfish prefers to stay in large shoals, so if you’d like to keep this fish in your tank, then buy at least 6 species at once, or even more, if you can afford it considering your tank capacity and algal covering in it.

Tank decor

The healthy fish is very active during the day. It tirelessly eats soft small algae from any surfaces in a tank. Add some preliminary soaked oak tree roots, round stones and tough tank plants, since catfish teeth aren’t strong enough to gnaw strong scapes of the tank plants, so if the fish is out of all the supply of fresh algae, it’ll need some additional feed.

You can create a model of the catfish natural habitat by putting plants with lots of leaves and preliminary soaked tree branches into a tank. Using of sandy bottom substrate will become a good ground for the tank plants and the fish waste products will stay on the substrate surface till the tank filter sucks them in.

A good quality filter with moderate or intense water turnover will keep the tank water clean and saturate it with oxygen.


The stomach of otocinclus catfish species caught in the wild is mostly filled with algae and other nutritive organic substances. In a tank the fish will eagerly eat algae from stones, tank plant leaves and glass walls.

However, otocinclus catfishes doesn’t depend on algae as on the main source of its food in the tank, therefore the fish should be fed with various special vegetable food, some feed with spirulina, flakes, frozen blood worm and gammarid.

Fresh steamed vegetables, such as lettuce, spinach, squash and green pea are perfect supplements to the diet. These additives can be given to the fish once a week for the night, but the food leftovers should be removed from the tank in 2 days, not longer. New squash will be the best addition to the diet.

You should boil them for about 2 minutes or put them into microwave oven in a plate with water for 30 seconds, after that fix them to some stone in a tank, so otos can eat them.

Tank mates

When choosing tankmates for Otocinclus catfish, it’s essential to consider their peaceful nature and small size. They are relatively shy and non-aggressive fish, so it’s best to select tankmates that won’t bully or stress them. Additionally, because Otocinclus are primarily herbivores that feed on algae and biofilm, it’s crucial to avoid pairing them with fish that might compete for the same food sources.

Since otocinclus catfish are peaceful, calm, they don’t grow to become a large fish and don’t harm anyone, they are perfect algae eaters, – they are ideal tank mates to any peaceful fish and they are welcome in any tank (for example: serpae tetra, glowlight tetra, black tetra, dwarf gourami, betta fish). The only tank that won’t do for oto cats, it’s a tank with large cichlids (flowerhorn, oscar fish, green terror) or catfish (sailfin pleco).

Here are some suitable tank mates for Otocinclus catfish:

Gender differences: male vs female

Determining the sex of Otocinclus catfish can be challenging, as there are no prominent physical differences between males and females. Unlike some other fish species where males may have more vibrant colors or specific fin shapes, male and female Otocinclus generally look very similar. This makes it difficult to visually sex them without resorting to internal examination, which should only be done by experienced aquarists or professionals.

Male has genital papilla and rows of modified denticles (odontoids). All of these are located on the bottom side of the tail-stem, where its body becomes a tail which is specifically twisted.

The role of this organ is still not clear enough, however some specialists suppose that it participates in the copulation and it is meant for the male orientation during this process when he embraces the female head with his body.

In most cases, the sex of Otocinclus catfish is not a critical factor for the hobbyist, as they are commonly kept in groups rather than specific breeding pairs. When purchasing them for your aquarium, it’s best to get a group of Otocinclus (five or more) rather than trying to identify specific genders.


Breeding is qualified as a difficult process. Though the otocinclus catfish was bred in captivity, still it happens occasionally. Although it’s easy to see between the male and female, to provide successful breeding it’s better to keep a group of fishes.

To stimulate spawning you should feed the fish with high protein feed, which consists of live feed, several times a day. Rather long courtship period that consists of the fights and getting the spawning spot ready precedes spawning.