Can fish be caught in all water tiles?
Fish can be caught in any body of water. Unlike pigs, cows, or chickens, fish don't exist until they're caught, so it doesn't matter where your water is.
You do need a minimum size body of water so that the lure doesn't get stuck on a block -- as long as the bobber is free-floating, you should be good. I've actually managed to cast into water falling from a "spring" block, have the bobber travel up to the top of the falling water, and then catch a fish.
From the Minecraft wiki as of 1.7:
- Take a fishing rod.
- Right click (default settings) while facing a body of water. (This can be as small as one cubic block, though the casting method becomes more difficult as your fishing area gets smaller.)
- Once the float has risen to the water's surface, watch for it to bob under the water.
- As soon as it bobs underwater, right click again and a fish should fly out of the water towards your feet. (The fish will not always land at your feet, it will sometimes fall short or even fly over you.)
And I have tested this myself, having finally decided to go back to vanilla and try the newest version. I was still able to catch a fish in 1 block of water, though getting the float in was difficult.
In the 1.7.2 update, it does not matter the depth, width or length of your water, you will always have to wait between 100 and 900 ticks (5-45 seconds) every time you cast your fishing rod. That being said, there are some variables that can change the waiting time for finding fish.
- Rain/Snow -- Wait time decreased by 25%
- Indoors/Underground -- Wait time increased by 50%
- Lure Enchantment -- Decreased wait time by 100 ticks (5 seconds)
More information about fishing can be found here.