Rainbow Shark Aggression

[New to aquarium]

I have a rainbow shark in a tank with 4 mollies, 2 cory catfish, a guppy, and a dwarf gourami. The rainbow shark has been relatively passive, getting along great with the other fish. Today he is showing aggression only toward the mollies. Two changes in the tank...I added some more plants and I noticed some baby fry (only 2), assumingly from one of the mollies. Are the fry the reason he is aggressive all of a sudden? Thank you, I am new to the whole aquarium thing.

 

[MapleNeil]

When I got my rainbow shark the petsmart employees asked what other fish I had. They said he can't go with guppies. I dont know about mollies but they also seem pretty peaceful. He can only live with other semi aggressive species that will stand up for themselves.

I have an apisto and a dwarf gourami and they have developed mutual respect and just avoid each other. But the shark chases the tetras around.