I once did an experiment with several types of newly imported fishes. (Large Wrasses, Tangs, etc.)
I offered these fishes frozen krill and/or frozen broccoli florets.
I was surprised to see Wrasses go for the broccoli over the krill.
Remember- feed the frozen (or blanched) florets. Freezing or blanching is done to break down cellular structure- not to get anything "bad" off the broccoli.