You are prohibited from gaming the mechanics to prevent yourself from going afk. So if the fish farm triggers you to cast/reel without your manual interaction then it is prohibited.

There are no prohibitions against just going afk. So if you want to just stand there and go afk to let animals spawn or wart to grow then go for it, so long as there isn’t something preventing you from going afk aside from you actually being at your keyboard or mouse and doing something. Keep in mind that you will be afk kicked after 15 mins of afk, and probably more importantly, someone who sieges you while you are afk will win the siege when you get afk kicked.