Honestly, when I see them doing this..I never get the impression that they are hunting. I know this is anthropomorphizing it, but they usually seem happy or trying to get my attention maybe.
In my previous setup. 50 gallon semi reef. I had MH lighting as well. 2x 175 watt. I cant recall noticing Bandensis displaying this passing cloud pattern. My offinalis sure did though. However, my attempts at raising Bandensis has shown improvements each time. At 4-5 months of age, this batch has grown larger then any I have ever raised including ones that reached a year old!
2 big differences in this attempt vs older ones include Flow and feeding. I have a LOT of flow in this tank. 2x vortech (full blast on reef crest mode) and return pump on Wavy Sea wave maker. Im also feeding large shrimps instead of shore caught crabs like I used to. Perhaps one of these factors if not both have increased thier health. Im starting to feel that flow does influence things, including viability of eggs as well. Ill write more of this soon on my main journal post...