These two stamp cards are part of a larger series, British River Fishes, issued in 1983. The other two which I no longer have were salmon and trout.
I've always said that collecting postcards, and in this case also stamp collecting, is educational. In many parts of France, they fish and eat a river fish called "sandre". They happily told me it was a hybrid of pike and perch but I see now from the stamp cards that in fact pike and perch are not only different species but different families.
So I investigated further and Wikipedia tells me that "sandre" or zander is called pike-perch only because it resembles both fish. Apparently it's considered a delicacy in many places in Europe. I can certainly vouch for it being very pleasant to eat.
Back to the present, and the task in hand. This is a post for Sunday Stamps, hosted by Violet Sky at "See it on a Postcard!" As usual, click on the link to see some other fishy tales.