Can Siamese fighting fish Live With Common otocinclus?

Otocinclus are small, peaceful catfish, about 3.3 cm long, that graze soft green algae and diatom films. They will not trouble a betta, and they keep to surfaces and the bottom while the betta stays in midwater.

What to watch is food, not aggression. Otocinclus can be outcompeted for food, and a hollow or pinched belly is the sign of a starving fish, a common problem in underfed groups. They are herbivores, so a spotless new tank gives them little to eat: add them once soft algae and diatom film have had time to grow, and check their bellies after feeding.

The water overlaps at 22 to 25 °C and pH 6 to 7.5, and otocinclus should be kept in groups of six or more in at least 60 litres. The usual betta caveat applies: it is best kept alone, with tolerant individuals the exception.