Answer: Yes, Anila, Sonia and others... the sarvangasana compresses the neck, the fish extends it. Some of u said the opposite, nevertheless, the general idea there is that one works the neck this way, and the other works the neck that way:)
Query: What would be a counter pose for a forward bend? Any forward bend? And why?
All these questions: they are here just to make u think a bit, so that the yoga school u try is a wise one. That u have the wisdom to chose a school or style which considers these aspects of the poses:) My own experience has been that most people who start to teach, including those who do advanced poses personally, do not bring much wisdom to the teaching. Why that is so, u guess:)