All anemones should be considered fish eaters and tube anemones being classified as such should not be singled out. In fact carpet anemones are sited to be responsible for more fish deaths than any other anemone. The issue with tube anemones is that they are nocturnal and their tenticles are all the way out during the night time hours. They will capitalize on a fish meal should it happen by but, no, they are not looking for it. They are detritus, scavangers and prefer small particles of food rather than larger meals. That said a curly Q or glass anemone will do the same should the opportunity arise.
Couple of facts about tube anemones, first they are not anemones, they are cerianthids in a class of their own. Also they have the least toxic sting of all other anemone species including aptasia. So, its safe to say that although it appears that they might have snagged your fish over night. The reality is the fish probably was already not healthy or sleeping and wandered too close to the animal. The outcome would of been the same had the the tube anem been another species of anemone.
