My sources indicate that Frontonia is primarily a cyanobacteria/diatom eater. one reference mentions the ingestion of small ciliates. These examples clearly show rotifer ingestion
Frontonia can eat just about anything. In some circumstances, they will even gobble up members of their own species ( http://onlinelibrary.wiley.com/doi/10.1 ... 1758.x/pdf ). And yet, they can subsist on bacteria, when they must....a very versatile creature!