Yes we are deadly serious. The scientific name of your shark cat is Hexanematichthys seemani, formly known as Arius seemani. These as with all Ariidae catfishes are sea dwelling catfish which only enter freshwaters to breed, the young fish then stay in freshwaters for a few months while they grow before heading down stream to join there parents in the sea where they stay until they become sexually mature and migrate back to freshwater to spawn. Your shark catfish will gradually become stressed and ill if it is kept in freshwater before finally dying from the lack of salt.
Pictus catfish are on the other end of the scale, being Pimeloid catfishes they dont tollerate any ammount of salt well and cannot be kept in salted water. If you intend to keep both fish then you will need two seperate tanks.