Well, lions dont always "chase" there meals. Although they are ambush predators, sometimes they are happy to wait for an opportunity to produce itself. And then they will envelope there meal in a swift second or two. And being present on the outside of his domain, peering inside may make him a little uncomfortable. I wouldnt be surprised if you just came home one day and found them or one missing!
Is he a captive breed fish or a wild caught specimen? That can make a difference!
Mollies and other small tropicals like guppys and swords breed rapidly, are cheap, and survive short time periods in salt water. Maybe if you want to feed your lion a live meal, try these cheaper alternatives! They are smaller and he may see these as an easier target for now.
As for aggression, they are already aggresive arnt they, i mean, they are predators. And what fish would you put in with a lion that u wouldnt want eaten or harrassed. I shore wouldnt put in a couple of clowns! lol