At 80% of his health he will initiate the "challenge" mode for this encounter. This means you need to either right-click him and interrupt it or let him call Arkatanthis the Destroyer.
As long as you make sure you can put Xilaxis into a corner, because he will constantly be knocking around the main tank, you should be fine to learn to properly joust the AOE's that are going off. His AOE's are not swipeable so they follow a very specific timer if you have people watching ACT.
The AOE's come rather quickly with only about 5 seconds between them so if your healers are not fast to group heal you will have problems. You may want to ensure two healers per group until you get good at this encounter.
Joust out for the ritual and make sure no one gets caught by surprise by any of the normal AOEs and you should have an easy time of this fight. He usually does one of his AOE's right after his Ritual so make sure you get the mob placed quickly when you are running back in otherwise he will AOE your raid and that will be bad.
There are no adds, so burn and enjoy the loots!
Just wanted to add a comment about a tanking position for guilds attempting easy mode, this was pointed out to me by someone else, but it is good info. If you tank him in the corner of the hallway before it angles off to the dead end, the tank can joust to the dead end and the rest of the raid back up the hall, this prevents the raid from getting frontals when the tank is moving back to position 
About every 40 seconds Xilaxis casts Arcane Dissipation on himself. This removes all detrimental effects that have been placed on him
The ring event of fishmen do mem-wipe about even 20-30 seconds. With about 300k DPS that our guild does we usually get the mem-wipe twice per fight. We just have the tanks fight for hate and have the rest of the raid close to the mob so the tanks don't have to run around for it.
On the third add we make sure one of the other tanks has complete hate around 50% so that the MT is able to get ready and pick up the namer when it comes.
It's not a full mem-wipe if I remember. Those first adds shouldn't pose that much of a problem. Chances are its a Hate issue with the tank. You might want to look at what the tank is doing to get the mob back because if his snaps arnt working then he is doing something fundamentally wrong.
I havent seen a need to tank swap the fishmen but if you have more than one tank in your raid then anytime you have a mob that mem-wipes pretty consistantly (like every 30-45 secs) then you should have every tank fighting for aggro from the start.
But, again I havent seen the need to multi-tank the ring event so your tank might want to look at what he is doing to acquire aggro. How much DPS is he doing for example is one thing to look at. Look at ACT and see how much threat is acquiring.
How do ya'll manage the 1st 3 mobs in the ring event's memwhipe? Do you treat it like a tank switch? Our MT was blowing through every snap he had and couldn't get aggro back till the mob had killed like 4 people.