Definitely at more than one place, but I just caught my last one at Lake Shiny
In the lumbridge castle can't you fish for bonito in flick fishing
you don't
ok first you need a harpoon and a rope too go to the fishing guild and use rope on fishing spot then use harpoon on the fishing spot too and there you after 2mins or more you get it.
lake shiny
Bazzacuda
Lure
you have to be patient and fight it slow theres no rush with fishing
just keep at it
In lake shiny.
go to the deep blue
go to the old pond