You can change the spec of your pets at any Stable Master (since Patch 11.1) Default spec: Tenacity
Diet
Fish - Raw Fish - Meat - Raw Meat
Taming Requirement
Blood Beast Taming
You must learn a special skill to tame Blood Beasts. It is taught by a Blood-Soaked Tome of Dark Whispers, a guaranteed drop from Zul in the Uldir raid on Normal Mode or above (i.e. not LFR). Once learned, this skill is account-wide.