These are passive tames. In my experience trying to tame a 145. You will find having a Basilosaurus will provide you with a mount immune to the shock.
Wear a combination of Riot and Scuba gear. Bring multiple sets. They will destroy your tanks and flippers if you get hit enough times. Lone eels do not deal enough torpor to be a substantial threat with the riot gear.
The hard part is feeding them. They will glow bright blue (without goggles on) when they have built up a charge, and charge you. Discharge a 7 second stun, bite and then flee.
Lure them into an enclosed area. Such as a trap for water tames or a river. This will reduce their mobility and make them an easier tame than in the open ocean. Because they will flee the majority of the tame if they have the room to do so.
-Results of 3/20/17 taming test on Xbox official servers.
It was stuck in shadowcave underwater, stood there for 30 mins and was tsmin it with meat. At 65% taming it decides to just do weird shit like making the taming bar go down 0.1 percent per 0m5 seconds couldnt feed against that, 30 mins of my life wasted again, thanks ark. Just dont try to feed it with meat.
Just tamed two on official. I built a small 2x6 box with a Dino gateway out of stone. Park my Dino nearby, then swim with flippers to gain aggro. Kited 4 into box, and i escaped through doorframes. 2 somehow got out through a hole in the ceiling before i could patch it. After a death and some shit, it's was super easy to feed them biotoxin without getting shocked. The stone walls protect you fully. I don't see an easier way if you build your own right.
The best way I've found to tame them is to use a basilosaurus,then lure a single electro away from the group and have it shock you (on the mount). Wait about a second for the shock to end and quickly jump off and spam E (keep biotoxin in the 0 slot). *A large school of these can quickly stun and immbobilze larger mounts and knockout players fairly quickly, so use caution!*
Use a basilosaurus. Wear scuba goggles,tank,flippers and then wear riot pants and gloves for torpor reduction. Only try and tame one at a time. Wait until it is 2/3 done discharging, and then hop off and feed it bio toxin before it runs away. When you hop off a basilosaurus, the electric immunity lasts a short while after getting off.