Yes. Level three farming is what you need to fish.

And farming and harvesting are the same thing. It depends on what platform you are playing, it's harvesting on palm, farming on pc.

i have finally done all puzzles except #15 i have read the guide, but i still cannot find whatever it is i need to find/do. I have moved the boulder and after i find the last puzzle, is that the end of the game? or does something happen and i'm able to explore more of the island?

Red crabs? I don't have any crabs yet and I've been fishing for years (gametime). I'll have to keep throwing my Master Farmers in the ocean until they catch some lovely seafood - but since the villagers don't actually cook anything - raw crabmeat? Yuck!

i can't get puzzle #15!!!! i have done everything else. can they explore more of the island or is that the end?

I'm afriad that is the end. At least as far as I can tell.

Go to the Virtual Villagers Guide for help with puzzle #15. You can find a link to the Guide in previous posts in this thread.
Good Luck

I don´t know if this is just in my game or something...but I read somewhere that the average time for the crops to grow is 100 mins...but I notice that is I water them just when I have half a field full..the next batch that I plant, only takes 13/11 minutes to grow!! ( on 2x speed) has this happened to anyone?

Yes it has happen to me a lot. But I did not have anyone watering it. I think it has more to do with how the farm counter is programmed and cycles, and not with the fact that you started watering it early.

fishing is the only unlimited food supply

I have done everything except puzzle 15 too. I know roughly where to find it but it took me so long to get to the stage that all my decent builders are dead. I am trying to get an adept builder to master builder and there is no building to do on the island only a bit of hut fixing so may take several years to complete this game!!!