The ruff (US: ruffe) or pope is a fish. I am finding it difficult to describe this fish. Some describe it as a freshwater fish found in temperate regions of Europe and northern Asia, similar to the walleye of the Great Lakes. Here the introduction of the fish has been disastrous, damaging to local populations. Predators have been introduce and poisons specific to this fish are being investigate to try to eradicate it. The ruff is usually 4-6 inches (10 - 25 cm) in length and will never exceed 10 inches, but is a very aggressive fish for its size. The ruffe also has a large, spiny dorsal fin likely distasteful to its predators. Others describe it as a small freshwater European perch, which sounds a friendlier fish altogether. Perhaps in its own native waters the balance has meant that it does not require to be aggressive. Could you send details (and a picture) to email@example.com if you know more?