Otocinclus, or Otos as they are commonly referred, are one of the most popular dwarf suckermouth catfish kept by aquarists. Their passive nature and adorable puppy-like faces make them a welcome addition to many community freshwater aquariums. Selecting fish to pair with your betta can often prove to be a daunting test of trial and error, but I’ve never met an Oto my bettas haven’t liked. While tenacious bettas are often threatened by the usual community-tank fish, they largely ignore the presence of Otocinclus catfish and ignoring is the best you can hope for in a community tank with a betta.
These pint-sized catfish top-out at about 1.75 inches (4.4 cm) in length and while they have been known to school, often prefer to hang solo allowing fish keepers the flexibility of keeping just a few at a time.
Otos are aggressive eaters. Pretty much, whenever they are moving, they are eating. Otos are herbivores and are especially fond of algae. They can bring rapid relief to an aquarium with an algae problem. That said, these fish are prone to starvation if there isn’t enough algae to keep them well fed. Unlike bettas, a fat Oto is a healthy Oto. Supplemental vegetation like blanched cucumbers or zucchini are favorites and algae waffers (found at any fish store) will cause them to flock. (Wait, can fish flock?… You know what I mean.)
When Otos aren’t eating they can be found resting in the the most random of locations. If you can’t find where your Oto is hiding, try turning over the leaves of your aquarium plants. They love to attach their sucker mouths to the bottom of a leaf and hang there for ages. They also love to suck their little faces against your aquarium glass where you can get an up-close-and-personal view of their powerful mouths in action as well as of their pale underside.
A few words of caution… Otocinclus are very sensitive to their environment and won’t tolerate poor water quality. Even low levels of ammonia, nitrite or nitrate can be fatal. Otos have a reputation for succumbing to pH shock so careful acclimation and monitoring of aquarium water is important. I suggest using the drip method for acclimation to allow them to slowly accommodate the new water. Otos thrive in water that is roughly 78˚F (25.5˚C) with a neutral or slightly acidic pH, similar to bettas. Like bettas, stability is the most important. Don’t drastically alter your pH for the sake of making it neutral. The rapid change is what causes pH shock.
Otos are wonderful fish and a joy to watch. If you have a fully cycled aquarium and are looking for a Betta buddy, a few Oto catfish may be the perfect addition to your community tank.