Chance is always powerful. Let your hook be always cast;
in the pool where you least expect it, there will be a fish."

– Ovid

Yes, the world of Britannia is Flat. Unless your path is blocked by land, sail long enough in any given direction, you will eventually find yourself right back where you started.

Fishing is a fairly slow skill to gain. Not much excitement there, but it's a nice change of pace from monster bashing. The occasional sea serpents keep you from falling asleep and the treasure maps, fishing nets and MIBs can prove to be quite lucrative.

For this skill, you will absolutely need a boat.  But don't rush off to high seas just yet, especially if you have no combat skills.   The important factor to remember is that you cannot gain indefinitely at the same spot. You need to move around, be it at seas or on shore. When you fish any given spot for long enough, you will eventually get the "The fish don't seem to be biting here" message. It means time for you to go to a new spot.

Skill	Where to Fish
0%	Buy skills from NPC fisherman
30%	Fish on the shore or in shallow water
75%	High seas using

You will gain from successfully fishing up something, even sandals and boots. Since it's harder to fish something in high seas, hitting the ocean below 75 is pretty much guaranteeing your gains will be next to nil. So stick to shallow water until you reach the high 70s.

The 8x8 method will be a must unless you wish to be fishing until Doom's Day before you GM. Finding your last gain square is a lot easier with fishing as you can use a Last object/Last target macro to find the exact spot where your last gain cast has been. If you were too slow stopping the boat or didn't see where your fish pole hit the water. Stop your boat, move back a few tiles and use the macro. You will see exactly at what distance from the boat your pole entered the water. Place your cursor right above that spot, move 8 tiles forward. Your cursor will still be at the same distance from boat but in new resource square. Use a last object macro and hit the water where your cursor is. You should get another gain.

Be ready to defend yourself from sea serpents and water elementals. Some of them roam the seas, but as your skills increase, you will start fishing sea serpents. Magery, archery or provocation are highly recommended combat skills for a fisher.

When you fish a monster, the game will give you a message indicating whether it carries a treasure or not: "You pull up a special fishing net along with a monster", "You pull up a sodden parchment along with a monster", or "Uh oh that doesn't look like a fish." If it says the latter, then you won't get a fishing net or an MIB, but you could still get a treasure map

Special Items

Sea serpents and krakens might carry a SOS, a MIB or Ancient SoS (the last two are for GM fisherman only), a fishing net (minimum 30 fishing skills), colored fishing nets (minimum 80 fishing skills) or a treasure map (minimum 90 fishing skills). To get the treasure from a SOS (MIB), you only have to double click the bottle to extract the message, go to the coordinates written there and start fishing. A minimum of 55 fishing skill is required though I strongly suggest to wait until you're GM to fish them up as the pre-chest loot could include large portraits which can only be fished up by a GM fisherman.

You need no special skills to use a special net, but beware. 1 to 4 of the following creatures will spawn: a sea serpent, a deep sea serpent, a water elemental or a kraken. Krakens are nasty. Chances are you won't survive it unless you have a very good healer with you. I have been doing special nets with my tamer. My mare can take the kraken but a lot of healing is involved. As I'm also a provoker, I generally provoke the sea serpents on the kraken to lessen the damage to my mare. For the treasure map, you will need a treasure hunter to dig it up.

Fabled nets can be found inside the chest fished up from an Ancient SoS. The creatures spawned from such a net are much harder to kill, including the Leviathan. I suggest using a bard to provoke the other creatures onto the Leviathan. One of the creatures could have a ship model, a seahorse statuette or an anchor as loot.

UO Automap:

Locating an MIB with a sextant can be quite trying. UO Automap (UOAM) is the answer to that problem. Note that for this to work, you will need a registered version of UO Assist. Copy the coordinates written in your MIB. In UOAM, go under the Places menu. Click Go To Location, then under Latitude/Longitude enter the MIB's coordinates. The map will jump to the SOS location. Under Places menu again, select Drop A Marker. You can then either go to UO menu and select Track Player or simply move your character one step in UO. The map will jump back to your current position and show a path to your MIB.  If it's located at the other end of the world (literally), you can either make it to the closest shore, dry dock your boat and recall to a closer city before hitting the seas again, or you could sail in the opposite direction, to the edge of the world. Once you cross it, it will take you to the other extremity, saving you a lot of travel time.