I submitted a manuscript on a novel and interesting finding on July 30, 2018 to a reputed journal. Following editorial review it went to peer-review. It is over 8 months, no decision yet. What should I do any suggestions!
The best thin g to do is contact the editor directly. Give them two weeks to respond. If not - try again.
If still no response - then I would consider submitting elsewhere. The journal in question may have a 'sister' journal where you could highlight what has occurred - which may speed up the review process in that journal.
Well, given the timing of submission I'd have thought it took a while to find reviewers. Depending on where the journal is based, it's hard to track people down in the summer. Let's say it was sent out in November/December (they don't send until after referees have agreed to perform). 3 months isn't unknown. Maybe just now is the time to chase things up with the editor? Maybe a month hence. Also, just calm down a little for everyone's sake. There's lots of research needs reviewing, not just yours.
One more example of the harmful, in fact anti-scientific effects of the obligatory pre-publication "peer"-reviewing system (see e.g. the attached papers)