Depends on their biology. I've noticed people tend to assume that beast people are 98% biologically whatever animal it is, and the remaining 2% is human head (teeth and ears only sometimes included), body, and limbs. And if it's a mermaid, the animal species is "fish", so it's cannibalism if they eat any fish, as if fish don't eat fish. /rant
There is a manga cover on that
A Study said, Beastman around 80% Human, and 20% Furry
Usually, Like Cat-beast they can eat chocolate, and somewhat resistant to catnip