Mythical fish

These fish would be extremely rare and difficult to catch, but be very large or decorative, about 6-10 blocks long. These would function as aquarium centrepieces for decorative players or can hold large amounts of value due to their scarcity, which is far better that the now reducing prices of epic fish. They would probably be about 1/10-1/15th rarer than epic fish and may have catch conditions (rain, caught in specific biome, etc).