Otocinclus catfish care guide

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

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.

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.

Golden otocinclus, we must say that it is quite seldom encountered in the wild nowadays. Maybe this was caused by the changes of its native habitat and land use conditions there, in South-East Brazil.

Scientific NameMacrotocinclus affinis; Otocinclus affinis
Common NamesOtocinclus catfish; golden otocinclus; dwarf sucking catfish
Range and habitatBrazil, Colombia, Peru
Size4 cm (1.5 in)
Lifespan2-3 years
Ease of keepingDifficult
Minimum tank size30 liters (8 gallons)
Temperature21–27 °C (70–81 °F)
Water hardness5-20 dGH


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. Lifespan is up to 3-4 years in a tank.

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

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).

Gender differences: male vs female

Otocinclus catfish exhibits rather pronounced dimorphism – female becomes larger and wider after they become reproductive. 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.


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.