You right. I just make this game for 2 days, so I can have some problems:))
Bait need to accelerate interest fish. Thus, she quickly seizes the bait. The more expensive the bait - the faster the fish will bite.
I will tell you a little about the parameters of the fish. They are that the fish may be hungry and interested. If she has reached the maximum of interest or she is very hungry, then she will grab the bait. Expensive bait is very attractive and speeds up these processes.
This is a job for the Jam and if I saw it before, I could improve these mechanisms:)
