As any wise fisherman will tell you, nobody is really sure what they will catch and with mixed lakes and similar speicies crossbreeding is not uncommon. In fact, three days ago I caught what I am almost sure was a bluegill/pumkinseed hybrid, it had the shape of and fins of a bluegill but the coloration and mouth type of a pumkinseed plus a little bluegill color. Anyway, panfish breed easily with each other and hybrids among them are more than common but other speicies spawn with each other as well, for example , some hybrids are known and others are not named. For example if a male brook trout spawns with a female lake trout, you get what is called a splake, it is similar in size and shape to a brook trout but has the markings of a lake trout. Another form of hybrid that also involves a lake trout is a fish that you will catch in lake superior known as a ciscowet. If a walleye mates with a sauger the offspring is known as a saugeye and if a northern pike and a muskie spawn, you get a tiger muskie. On rare ocassions anglers catch mutant speicies like the silver pike, a mutant speicies of Nothern pike. Different forms of the same fish can be caught, a few examples are the northern largemouth bass and the florida largemouth bass and the northern bluegill and the florida bluegill. The muskie is divided into three subspeicies, the spotted muskie, the barred muskie and the clear muskie. You may catch a number of crossbreeds and subspeicies or evan mutants so if you catch a fish you don't know, look into it, you may be suprised. In the picture to the left, this is a Saugeye
