While doing my Daily Assignment today defeating an O'leary Swindler in Newgate Prison in Marleybone. I couldn't believe my eyes to see the cool crowns pet Betta Fish dropped. There's no info on the Wiki. Good luck obtaining your own Betta Fish
You might have accidentally not looked at the reward you got from Daily assignment. The Betta fish is a known reward that can be given from daily assignments from the Day 5,10, and 15 chest. I myself have gotten the fish from doing a visit a location assignment.
