What exactly does bait size mean?

[fiery iris]

I'm not clear on what the different sizes actually do. Does large bait mean you're more likely to catch large fish? Or does it just mean it's the largest improvement to your chances of catching a fish? I'm trying to catch an arapaima with small bait, and I'm not sure if it's helping or hindering my efforts!

[bold timber]

the size of the bait correlates to the size of the fish. try using large bait for that one

[fiery iris]

thanks!