Hi Rebecca - in the absence of a Reg. No., then I doubt that we can help, unfortunately. Quoting Raymond Knotely - 'Popular Glass of the 19th and 20th Centuries' (Miller's) - and where he was writing with regard specifically to these pike - and under the heading of Plagiarism (p. 54) - he says - ""It is not unusual to find different-sized versions of the same basic form, and this is the case with regard to the M. W. (Manchester) pike etc. ""Sometimes, however, it can be confusing to find a version of something you already have, but without marks and with subtle differences. Plagiarism was common, and a great deal of contemporary copying went on ............ etc. etc.""
There are several known forms of this flower trough - all opalescent I think, and they come in blue, uranium and uncoloured opalescent - although I'm unsure whether all of these colours emanated from Manchester, c. 1880 - 1890.
Looking at the screen image of your pike, my thoughts are that the dorsal fin appears more prominent than the book pix of the M. W. pieces, but that might just be my needing Specsavers, again. How was your fish described when purchased, and was it a local buy?
If you search the Board's archive under 'opalescent pike/glass pike etc.' you should get some interesting reading matter - I had some vague thought that I'd posted a picture of the original factory drawing some year or two back - will re-post if I can find it. We do have other members here who have posted pix of their own pike, so fingers crossed they can be persuaded to share their better informed experiences and knowledge.

P.S. If you look under the 'Ancoats Exhibition 2016' in the attached link from Neil's interesting site - you will see an uncoloured opalescent example, plus what appears to be a darkish green non-opalescent pike. I think they also come in blue non-opalescent.
https://sites.google.com/site/molwebbhistory/Home/registered-designs/derbyshires-unregistered-pressed-glasscopy of TNA original M.W. factory drawing dated 14th July 1885 ....
http://www.glassmessages.com/index.php?action=dlattach;topic=64398.0;attach=204046