The size isnt really the big difference here. The activity level is what to be concerned with. The smoothound wont live in anything less than 1000 gallons. A leopard needs a multi-thousand display tank and your common horn shark needs at least a 300 gallon. These sizes are approximate. If the biggest tank you have is a 125, you could do an epaullette, coral catshark or bamboo families for a while before they outgrow it. At least the first and last sharks will. So yes, you are limited to the "boring" sharks that never seem to stop amazing me every time I take a seat in the living room.