I know you can fish in one spot to get to 200, but what is required to get to 250? Do you have to change to doing trade skill combines?
Yes, you need to purchase the cap-raise aa line as well as do unique combines (i.e. each recipe you learn goes towards the skill-up, but only that first time) to get skill-ups past 200 in fishing.
SoulBanshee's tradeskill parser will read your output file and tell you which combines you are missing so you know which combines to finish leveling. There is a post about it on the forums.