Oto (Otocinclus mariae)

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Dwarf Oto

Otocinclus mariae

57 Litres (15 US G.)

2.5-3.8cm (1-1.5 ")




6.0 - 8.0

21.1-26.1°C (70 -79 °F)

8-20 °d

1:2 M:F

Pellet Foods
Flake Foods
Other (See article)

3-5 years



Additional names

Dwarf Otocinclus, Dwarf Otto


Difficult. Females are slightly bigger than males.

Tank compatibility[edit]

An excellent peaceful community fish. They are best in groups of their own kind.
There are records of suckermouth fish sucking on slime coats of slow moving large bodied fish such as Angelfish and Discus. However it should be noted that the Otocinclus is one of the few sucker-mouth species which feed almost exclusively on algae. Typically the suckermouth species that attack the slime coats of other fish are the omnivores Pleco's or Chinese algae eaters.


Otos will mainly graze on some soft algaes, primarily diatoms, and blanched vegetables such as Zucchini (Courgette), Carrot, Potato and Cucumber. They may also accept some algae wafers, but it can take some time to wean them onto these. They will not eat hair algae or green spot algae.

Feeding regime[edit]

Otocinclus varieties are algae eaters, but it is important to note that they are an obligatory algae eater species; they will only eat soft green algae and diatomic algae. Most otocinclus will readily eat these types of algae, but it is essential to supplement this diet with either zucchini/cucumber or gel food, as they tend to clear the edible algae in an aquarium too quickly to allow it to regrow.
Zucchini or cucumber can be sliced, blanched, cooled, and placed in the aquarium (one slice at a time) for at most 48 hours before it deteriorates and requires removal. If a slice is untouched after 48 hours, replace it with a fresh one. It takes time for the fish to understand that zucchini/cucumber slices are edible.
The most reliable alternative is Repashy Soilent Green gel food, either spread on an object such as a decoration to mimic algae growth, or fed in a block. Old food should be removed after 24 hours, and the food should be placed far from filter inlets as it can easily be sucked into the filter and rot.
Care should be taken to ensure that newly bought otocinclus are accustomed to alternative foods such as gel food or zucchini/cucumber slices before being added to a display tank; in the case of inadequate algae growth, an otocinclus may starve to death if it does not understand that gel food is, in fact, edible.
More information on feeding new otocinclus is in the special notes section.

Environment specifics[edit]

A planted aquarium is a must. Ensure you get them in a shoal of at the very east 6. They are a nervous fish if not kept in groups and have been know to die from stress if not kept as so. As this small fish eats whilst resting on a surface, they are easy targets for larger fish in the wild. Prefers to rest on vertical surfaces such as the glass or slate, will also rest on broad leaves.


They tend to rest on any object, including the front glass so you'll get plenty of views of their underside.


The colouration on this Oto differentiates from other similar Otos in a very subtle way. The belly is pale with a bold black lateral line running from the nose to the caudal peduncle, it sometimes breaks before the caudal fin. The top half of the body is mottled grey. On the caudal peduncle is large black diamond shape, it should not be rounded and be quite angular. There are two vertical black bands visible on the otherwise-white caudal fin.
This fish is often incorrectly identified as Otocinclus affinis, Otocinclus macrospilus or Otocinclus vittatus.

Special note[edit]

These peaceful community fish are often starving when you see them in the average pet shop and consequently they have a reputation of having a high mortality rate within the first month of ownership. They are wild caught, traveling hundreds of miles after being harvested from rivers, and many are emaciated when they reach a store. The catch method also includes dumping an amount of cyanide into their habitat to slow them down for capture, and many are weakened due to that as well.
Do NOT buy any otocinclus catfish if your display tank/quarantine tank is not cycled. They are very sensitive to water quality and their health deteriorates rapidly when put in an aquarium that has poor water parameters. Proper acclimation is also essential, drip acclimation being the preferred method. Ph and temperature shock can kill otocinclus catfish.

Do NOT buy any otocinclus catfish if there is not already a large amount of soft green algae or diatomic algae. It may take them a while before they learn to eat alternatives, and if there is insufficient algae they can starve in the mean time.

Do NOT buy any otocinclus catfish if you do not have space for a shoal of at least 6. The number makes a huge difference in their behavior, and they will not thrive if they are in an insufficiently numbered group.

Ensure that you look at their bellies carefully in the shop and if they look very thin or hollow bellied then tell the shop to feed them more algae tablets. These fish need to eat all the time.


External links[edit]