I have been doing a little more research and I might now accept that this could well be a "Recade". This is where it might get a little confusing. I am now not talking about Benin City and Yoruba people of Nigeria but of the modern state of Benin which was known as Dahomey. There is a good possibility that we are looking at a very styilised fish form recade. The recade Bocio of Dahomey Kings take many animal forms. The last king Behanzin, had Bocio {sort of power totem} in the form of fish or shark and often depicted as a fishman or sharkman. Dahomey Bocio art objects are made to appear arcane and mysterious with an intentional roughness. Being Dahomey would explain the lack of Benin City {Nigeria} traditional imagery. This is assuming that it is not something from the Cross River region of the Nigerian/Cameroon border but is does fit with Dahomey recade norms. Some links and picture. You can also search this site for basic info.
http://www.quaibranly.fr/uploads/tx_..._Abomey_EN.pdf
Note the bottom line.
http://raai.library.yale.edu/site/in...&image_id=1696