I kept a rainbow shark with ottos & they got along just fine . Ottos are small enough that they can hide in your plants if the tiger barbs get nippy . Just take a good look at the ottos in your dealers tank before buying them . Look for the fat ones & avoid any with sunken bellies . A lot of people seem to have problems keeping ottos alive , so make sure to buy the plumpers . If they are starved , the bacteria in their guts needed to digest plant matter will die off , causing them to eventually die .