A good summary of this research can be found here and it has also drawn a lot of attention because of its unique and very significant findings. The results can be succinctly summarized as follows. Lionfish use a clear action during which "they shimmy their tails and fan out their fins" to recruit other lionfish to hunt (they don't do this when they are alone or if potential prey isn't around), fish who hunt together cooperate and catch a bigger meal than each would have caught alone, and the fish take turns sharing food. When the fish are alone they swallow prey rapidly, but when they hunt together, researcher Oona M. Lönnstedt notes, they "seemed to be polite."
Redouan Bshary, a renowned expert on the social behavior and cognitive abilities of fish and with whom I've had some very enlightening and educational discussions about the amazing lives of fish about whom I know very little, notes that fish are much more complex than people give them credit for and that this study, in which turn-taking was observed, could "really shake up old prejudices about the mental powers of fish."