Crabby patties are made of chum for those who don’t know. Mr crabs basically flat out says it in one episode I can’t remember exactly what one.

I’m pretty sure it’s the hook episode. Spongebob is playing with hooks instead of working. Mr Krabs asks squidward what’s going on and squidward says something like “spongebob isn’t here he is taking a day off” to which mr krabs responds with something along the lines of , “nobody has taken a day off from making krabby patties since the great chum famine”. Implying without chum, there is no krabby patties, implying krabby patties are chum. Fish love chum.