Hey yall!
This is a pic of a "floy" or spagetti tag in the back of a fish. It has been the main type of tag used in Alberta for many years to mark fish.
Often a coating of a brown algae will coat the tag and the number and color of the tag are not evident. It is not too difficult to scratch the coating off with your finger nail (NOT A KNIFE).
If you catch a fish with such a tag, scratch the tag and record the color, the number, the species of fish and the location as best you can. (a fork length in mm and a picture would be great too)
Supply this information to the nearest Fish & wildlife office (best to talk to a "fisheries person if possible). You may be helping fisheries management a lot in following fish they have marked.