Pretty much any trigger you get, and they would have to be babies like an inch; could live in there maybe 3 years max. Humu grows slow and you can find small juvis about 1 to 1.5". You can find baby clowns and bluelines about an inch, they also grow slow but are more aggressive, you'll maybe have about 2 years with them. You might get lucky and find a niger somewhere around 1.5" but they grow faster, maybe 2 years. Those are the most common triggers you can find at 1" to 1.5", some say babies are difficult but I have raised many and have not found that. If you find a starry, rectangle, or bursa at that size; they are similar to the humu in temperament and growth rate. Don't get a pineapple baby they grow very fast. I'm raising a clown and blueline now in a 40g, they'll go to a 125g in a couple of years and be there for maybe 3 years or so before going to a very large tank.