5.5" that was peaceful. Definitely wanted 'his' food though. They don't typically eat other fish, not sure about like a tiny .5" clown goby or something with a huge 10" tusk, but had mine with a ~1.5" juvi porkfish, no problems.
The problems arise from Tusks, when they fell cramped in smaller tanks (75gal'ish) and there's competitive feeding and you add another mouth to feed (so to speak). Mine had to warm up to a Cuban Hogfish I added. Never problems, just let him know the Tusk is boss lol.