The Otocinclus Affinis (often referred to simply as an Oto) is one of the most useful fresh water aquarium sucker fish.  It’s a small, peaceful, algae eating machine that looks cute to boot. Hailing from South America this little schooling fish prefers tropical faster moving waters, and groups of six or more.

Despite it’s schooling tendencies, it is commonly placed in smaller tanks without others of it’s species.  They tend to do okay in these settings, but please be aware these are a social fish.

The Otocinclus hails from the Amazon basin in Brazil. It lives in faster moving streams and rivers, and that is generally where it is caught for sale all over the world.  Because it is more cheaply caught and shipped than bred, it is important to be careful and quarantine all new Oto’s before you introduce them to tanks.

Otocinclus Care

The Basics

  • Size: 1.5″
  • Tank: 1 Gallon
  • PH: 5.2 – 7.5
  • Hardness: Soft to Hard
  • dH Range: 4.0 – 20.0
  • Temperature: 68 – 82 °F
  • Swim Level/Strata: Bottom to Middle
  • Water Type: Freshwater
  • Water Movement: Moderate
  • Lighting Needs: Low – Medium

Introducing Otocinclus to Your Tank

When you get new Otocinclus there’s a good chance they are going to have been wild caught, and shipped from South America.  This does mean that unless you get tank raised Oto’s you’re going to want to quarantine these fish for around 2 weeks.

Also make sure that the tank has at least some algae in it, not all Otocinclus will feed on algae wafers immediately.

Otocinclus Affinis Aquarium Setup

The Otocinclus is rarely the centerpiece of an aquarium.  They are a hardy fish that can be added to most freshwater aquariums to help keep down algae, and eat left over food.

Otos are peaceful creatures, they’ll survive well with most other peaceful fish and creatures. They are also fast, and small, so they can often survive with more aggressive fish as well, including Bettas.

Otocinclus are schooling fish, so ideally you would want to get around six of these fish at a minimum, however they are commonly kept as the sole fish of their species successfully.

What the Otocinclus Affinis does need is an algae rich tank, so it’s better to place your new Oto’s in a well established tank that is relatively algae rich.

Otocinclus Feeding

Otocinclus are completely herbivorous.  They exist nearly entirely on a diet of algae. You can treat them with the occasional vegetable, but make sure you take it out if it doesn’t get eaten.

If your tank runs low on live algae, then supplement the Oto’s diet with algae tablets/pills and look at potentially starting an algae farm so you can replenish low algae levels.

Otocinclus Aquarium Maintenance

Unless you have managed to purchase tank raised Otocinclus, your Oto’s may be more sensitive to disease due to damaged fins and gills (from shipping). This means that on top of an initial quarantine you’ll also want to keep a clean, well filtered tank and do regular water changes for at least the first two months, be careful not to clear out too much of the algae though.

Otocinclus Breeding

Breeding Oto’s is no easy task, and it is often seen as a fluke occurrence rather than following any specific steps.

Since we haven’t personally managed to breed Otocinclus we’re going to leave this for now, until we can find any reliable information (or find a way to do it ourselves!).

In terms of general breeding advice for Otocinclus catfish however we can say that following the natural environment can help. Lowering the water level during a water change and adding slightly colder water can help. Also try lowering light levels and ensuring the tank is as peaceful as possible.