AFAIK Vobla is typically one specific fish, namely the "Caspian Roach". That said, its pretty tasty. If you get some there pick up some of the beer as well.
I am impressed with your depth of knowledge of dried Russian fish :-)
Both of these words can refer to either specific species of fish, or to the method of preservation, depending on the region. Whichever word you use, the sales person in that store is sure to rudely point out your mistake. Like you said, the Soviet level of service is part of the experience.
