Rare Flowers affect the Basilo (slightly inconsistently) allowing you to kite it into your own water pen for a super safe, even easier tame involving much less swimming about. Seems to require you to eat at least 2 flowers to trigger the aggro effect, and it loses aggro the second the effect ends.
The easiest way to tame this whale is to bring a Baryonyx with ya to deal with the manta's and sharks and to wear scuba gear. Once the sharks and manta are dead just passive tame the whale with either prime meat or Theriz Kibble.
This is by far one of the best water tames, has insane health regen and if you boost melee you can easily solo kill mosa and tuso alphas, good for jellyfish because cant be stunned. And keeps you warm underwater!
When it comes to taming this guy, I personally like to hop on a high level spino. The spino easily deals with anything surrounding the basil, and then go ahead and start feeding it. I use kibble, it's a pretty fast tame, but the time between the first and second feeding feels like forever.
When taming the time between the first and second feed takes forever. To avoid this move well out of render and back again and it will be ready to feed 👍 Also upon your return be sure to kill everything in the area before continuing. Essentially an under water rex. great all round beast.