Hi mate thanks for playing,
It's not a fishing hook it is a fishing book, but to access the information about a fish you must catch it first.
Once catch you can clic on the fish name you just caught in theb ook and you'll get the book working.
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Oh yeah sorry, i didn't had time to put more explanation hud, so you clic on a squares and wait until a bar appears on the left of the screen, once this bar appear press space fast enought to fill it and catch the fish.
Now that you say it it's true it's missing some prior part to udnerstand the gameplay sorry about that.