Lionfish in the Cretan and Libyan Seas feed mainly on small fishes, swallowing them, according to a preliminary analysis made in the ichthyology-lab of HCMR in Crete (link).

In the frames of the project, lionfishes have been collected and are kept in tanks at the University of Crete, for behavioural studies. In this video you can see the feeding of lionfish on alive fish, as -for the time being- they refuse to take any other type of food.