Dwarf lions are hardy fish as long as you know that they are eating. Never buy a lion if you do not see it eat in the tank, even if the store just puts ghost shrimp in the tank to see it eat. Some lions are caught with cyanide, and thus will arrive at a store and not eat at all. Refuse to buy a species that does not eat, because if this continues to occur with lions being caught with cyanide, the store will stop buying from that particular supplier if the customers refuse to buy them, and that particular supplier will eventually stop buying from that person who caught the fish because no one is making money off of catching fish with cyanide (aside from the fact that it is deadly to the fish).
To answer your original question though, they are hardy and not very prone to disease. Get fish that are big enough so that they cannot fit in his mouth however.
