Three to five years, if they settle
An otocinclus that survives its first weeks in your tank is a genuinely hardy little fish, good for 3 to 5 years and sometimes more. The species' reputation for delicacy comes almost entirely from the front end of its captive life. Nearly all otos in shops are wild-caught, shipped long distances, and held in bare tanks where they cannot feed properly, so the fish you buy may already be running on empty. Everything about keeping otos for years, rather than weeks, flows from understanding that the first month is a recovery programme, not ordinary fishkeeping.
The starvation trap in a spotless tank
Otos graze aufwuchs — the film of algae, microorganisms and biofilm that coats leaves, wood and glass in a mature aquarium — and their gut depends on it. In a newly set up or aggressively scrubbed tank there simply is not enough of it, and a group of otos can starve in water that tests perfectly. You can read a new oto's condition at a glance once you know how: a fish that has been eating has a rounded, slightly bulging belly, easiest to see when it rests on the glass, while a starved one is pinched and hollow behind the head. Buying only plump-bellied otos, from a tank where they have clearly been feeding, is the single best lifespan choice available to you.
An established tank is non-negotiable
The oto tank should be months old, with algae allowed to live on the back glass, wood and plant leaves even if you clean the viewing pane. Soft to moderately soft water, gently acidic to neutral, warm around 73 to 79°F, and steady: like most small wild-caught fish, otos tolerate their home conditions far better than they tolerate change. Keep them in a group — six is a working minimum for a fish that feeds and rests socially — and with peaceful tankmates that will not outcompete or nip them. Strong flow is welcome where it is oxygen-rich, but a gentle tank with heavy planting suits most home setups better than a riverine current.
Feeding beyond what the glass provides
Even in a mature tank, assume a group of otos will eventually eat the grazing down faster than it regrows, and budget food accordingly. Blanched courgette, cucumber and green beans weighted to the bottom, algae wafers left overnight, and purpose-made grazing foods pressed onto wood all disappear steadily in a healthy group. Rotate the offerings, remove uneaten vegetables before they rot, and watch bellies at the weekly check: a tank of round-bellied otos is succeeding, whatever the algae situation looks like. The fish that needs prompt help is the one sitting apart, belly hollow, barely grazing — isolate it with food in a quiet corner of the tank and re-check water quality the same day, because a settled oto that stops eating is giving you early warning worth acting on.
Those twice-weekly vegetable drops are easy to forget in a busy house, so KinsLe Care Teams lets you assign oto feeding as a named duty to family members in turn, with each completed feeding marked off by a timestamp.