Otocinclus
Otocinclus vittatus
Small algae-grazer for mature planted tanksIntermediate
- Lifespan
- 3-5 years
- Size
- 3-5 cm (1.5-2 in)
- Social needs
- Social shoaler - keep 6+ together
- Time
- Moderate (daily feed, stable mature tank)
- Cost
- Low-Medium
- Diet
- Herbivore (algae/biofilm grazer)
Overview
What is this animal?
- The Otocinclus, or oto, is a small suckermouth catfish from South America and one of the better genuine algae-grazers for the planted community tank.
- It works over leaves and glass, removing soft algae and biofilm too delicate for larger plecos.
- Its intermediate rating is well earned: most otos die not because they are hard to keep but because they are sold half-starved, often wild-caught, and rushed into immature tanks before there is enough biofilm to sustain them.
Temperament
- Otocinclus are peaceful, gentle shoaling fish that feel secure and graze openly only in groups of six or more.
- Singly or in small numbers they hide and stress, so a true shoal is essential for natural behaviour.
- They are harmless to tankmates and well suited to nano and planted communities alongside small tetras, rasboras, shrimp, and corydoras.
- Keep them away from boisterous or large fish, which intimidate these small grazers.
A good fit for
- Mature, algae-rich planted tanks
- Nano and peaceful community setups
- Keepers wanting safe algae control on plants
- Aquarists who select round-bellied stock
Common mistakes to avoid
- Adding to a new tank with no algae/biofilm
- Buying thin, starved, hollow-bellied stock
- Keeping fewer than 6 (they shoal)
- Salt/copper medications they tolerate poorly
Enclosure
Minimum 75 litres (20 US gallons) — for a group of 6
Cannot be kept alone. The minimum is 6, and the space above is for that group.
- Keep a shoal in a well-established, fully cycled tank of at least 75 litres (20 gallons) with a stable, mature growth of algae.
- Maintain 22-27C (72-81F), pH 6.0-7.5, and clean, well-oxygenated water with low nitrate.
- Never add otos to a brand-new tank; they need an aged setup with soft green algae already growing.
- Provide plants, driftwood, and gentle flow.
- They are highly sensitive to ammonia and nitrite, so the cycle must be solid before they arrive.
Supplies
Setup
- Tank and stand
- Filter
- Heater and thermometer
- Substrate, plants and decor
- Liquid test kit
- Dechlorinator and starter supplies
Ongoing
- Sinking wafers or tablets for bottom-feeders
- Algae or spirulina wafers
- Frozen bloodworm, daphnia and brine shrimp
- Untreated aquarium driftwood (essential for clown plecos)
- Courgette, cucumber and spinach for blanching
- Veg clip or a stainless veg skewer
- Feeding tongs or a pipette for target-feeding
- Fine sand substrate for corydoras foraging
Safe substrate: Inert aquarium gravel · Fine, smooth sand · Aquasoil for planted tanks
Care routine
Daily
- Check temperature and equipment
- Head-count and look everyone over
- Sinking food at lights-out
Weekly
- Top up evaporationevery 3 days
- Check belly profiles
- Clean glass and clear algae
- Test the water
- Water change and gravel vacuum
Monthly
- Trim and thin the plantsevery 2 weeks
- Check supplies and reagent dates
- Check the driftwood
- Rinse the filter media
Less often
- Replace chemical filter media (Carbon/Purigen)every 2 months
Vet: Quarterly bottom-dweller review — every 3 months
Top resources for more info
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Diet
- Otocinclus are dedicated herbivores that graze soft green algae and biofilm.
- In tanks with insufficient algae they will starve, so always supplement with blanched vegetables such as courgette, cucumber, and spinach, plus quality algae wafers.
- Many new otos arrive emaciated and need immediate, reliable feeding to recover; a sunken belly is a danger sign.
- Keep a steady supply of grazing food and vegetables.
- They cannot subsist on commercial flake intended for other fish.
Health
- The biggest killer of otos is starvation, both before purchase and in algae-poor tanks.
- Combined with their sensitivity to poor water and shipping stress, this makes the first few weeks critical.
- Choose round-bellied, active individuals and acclimatise them slowly.
- They tolerate medications, salt, and copper poorly, so treat with care.
- Check belly shape daily: flat or sunken means underfeeding.
- In a mature, stable, algae-rich tank with clean water they settle well and live several years.
Is your enclosure big enough?
Is this urgent?
In a fish tank the patient is usually the water. Test before you treat — dosing a healthy tank for a disease it does not have makes things worse.
Go now
Today
Soon
Never add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.
This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it — and the time to find one is before you need one.
What it really costs
Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.
Bedding and substrate
Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.
Safe
With a caveat
Never
This is our general list for freshwater fish. We have not built one specific to Catfish yet.
My kit says 0.25 ppm. Is that dangerous?
A liquid kit measures total ammonia, but only the un-ionised fraction is really toxic, and that fraction is governed by pH and temperature — each whole pH unit multiplies it roughly tenfold. So the same reading can be nearly harmless in one tank and lethal in another; this works out which one you are in.
Compare with other animals
The same axes for every animal, side by side — the way the guides are written makes that a fair comparison rather than two articles.
Catfish, side by side
Same axes, same care guides — the honest way to choose between types.
See all Catfish side by side →
