Not sure you need a guide.
- the vendor sells rod and bait. This bait is for meadows level fish.
- meadows level fish give something that makes BF level fish bait, so you can catch trollfish.
and so on. Each higher up fish group has 1 that makes better bait.
- you can get the better bait by trolling the shore for landed fish, bypassing the lower tiers for now if you are a veteran player.

- fish now have tiers, visually making them bigger and fatter, and giving more raw fish when chopped up. The higher the tier, the more stamina drain.
- raw fish now comes from the cooking pot. This appears to be an aggravation created because you need the same fish for bait -- the pot lets you make the choice between bait or food.

- as before, fish traps on the shore are super effective. Moreso than ever, and with the annoying bait mechanic (even in the right zone with the right bait, you get 'the fish is ignoring your bait' messages from strays). I recommend just making a fish trap, which is raise/lower/level the shore where it is often high wave/stormy and put a lip on the edge (raised higher, above the water when calm). Then just raid it when you need fish.

there are some new recipes that use some new fish, not just the bait. But generally speaking, its just fish and the extra complexity adds nothing. It would be FINE if higher tier bait caught anything that level or lower. Because that is not the case, its frustrating. There are enough good foods out there that fishing remains optional.