Followed your "advice" & looked it up.
From:
http://www.reefkeeping.com/issues/20...ture/index.php
I have found these fish to grow fairly quickly when fed properly, and they will easily become 10 inches long within one year [Figure 13b].
Figure 13a. A juvenile Russell lionfish, similar to what is commonly seen at local pet stores. This little 4 inch juvenile possesses long flowing pectoral fins and will grow into a foot-long fish eater within one year. Photo by Frank Marini.
Figure 13b. The same lionfish 1 year later. Sure, I feed them well, but look how big they get. Russell's lions are eating machines, and will easily outgrow a 55 gallon aquarium within 8 months. If you noticed that the body of this fish is getting thicker and the pectoral fins are appearing shorter, you are correct. Older Russell's lionfish have fat, squatty bodies and relatively short pectoral fins. Photo by Frank Marini.
From Scott W. Michael's Marine Fishes guidebook:
Every description of every species of lionfish (dwarf & otherwise) states:
"Will eat ornamental shrimp & smaller fishes."
It may be small now, but how about a few months from now when your shrimp & fish are small enough to fit into the mouth of a growing lionfish? If you google image search or check in Scott Michael's book, the Zebra dwarf lionfish looks totally different (with regard to markings), while the Russell's lionfish is what your pic looks like.
Anthony