While I think Racream's ideas could be beneficial, I'd rather stick with buffing the low end of fishing to stabilize it rather than increasing the top end so much.
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The top end doesn't need to be buffed as hard, in my opinion. Instead, the stronger buffs come at the bottom to normalize prices to a closer average.
With the adjusted prices, your minimum haul would be 50 gold if you only got terrible pufferfish and no gargs, and your best haul would be 198 if you had only blue marlins and 2 blue marlin gargs (which is next to impossible). Most people would get around 100-120g per boat, which is about in line with the amount of time you'd spend (around an hour if you fished twice for a full boat). That means most people would experience about a 200-240g per hour earning rate, boosting fishing up close to the pure-gold values of most other work.
Remember, we aren't trying to make this the best source of income in the game. We're trying to make it better than it is in comparison to other professions. People still need to be out running packs, farming purses, and so on at roughly the equivalent rates. Otherwise, everyone will have a bunch of gold from fishing and they won't be able to buy anything because everyone is out fishing.
We're trying to stabilize it so you don't feel like you're wasting your time with it, that it can be decently profitable.
If you do something like the changes I listed and make chums and lures cost half or less the vocation they are now (I'd recommend 1000 for chum and half-cost lures), I think you'd have a health industry. Not overpowered, not underpowered, just a profitable way to make money that isn't running packs or farming purses. And more fun in general.