Guppies and mollies are a welcomed live addition to a predators diet. These fish have similar protein and fat as their marine cousins, they are in fact brackish and even easily converted to full salt. The basis to the warnings of feeding fresh water fish is really towards goldfish and rosies. These fish contain a large amount of thiaminese, which binds vit B1 and leads to premature death and goldfish contains a large amount of the wrong fat, which leads to fatty liver disease. Rosies have a bone structure which binds in the gut, causin bloat and death. I know I'm long winded but I'm a person that likes to know why. Live guppies and mollies will aid in a long life for the fish you are keeping.