A fish is a fish...right? Not quite. Lampreys and eels are fish; as are sharks, skates and rays. The sea horse also fits into the classification of a fish, though to look at one you might think otherwise. Some fish can survive "out of water" and some have actual lobed fins like the limbs of other animals. Scientists place the types of fish in the world into three categories or groups: the jawless fish (Class Agnatha); those that have a skeleton made of cartilage, a firm, flexible connective tissue made of protein (the cartilaginous fish or Class Chondrichthyes) ; and those that have a skeleton made of bone (the bony fish or Class Osteichthyes). The groups differ in their means of reproduction. In bony fish and jawless fish, the majority of females discharge their eggs into the water for fertilization by milt (semen) from the males. In most cartilaginous fish, as in mammals, the eggs are fertilized within the bodies of the females. Since cartilaginous fish (sharks, skates and rays) are typically marine, they are not found in the present day lakes of Saskatchewan. The Chestnut Lamprey, a jawless fish, can be found in some locations in the province. Bony Fish (Osteichthyes) Scientists classify all organisms into groups using a set of parameters. Bony fish belong to the Kingdom Animalia, Phylum Chordata and Class Osteichthyes. Further classification places fish with more similar characteristics together into orders, families, genera and, species. Bony fish are characterized by the presence of a skeleton made of bone (as opposed to one made of cartilage like sharks, rays and skates). Bony fish can be further subdivided into two groups based on the construction of their fins. Ray-finned fish encompass the majority of bony fish living in Saskatchewan waters. As the name states, the fins of these fish are constructed of skinny rays and flesh. These rays are easily seen on the fins of pike, sauger or any other popular angling fish. Lobed-fin fish are present elsewhere in the world, but do not have any representatives in Saskatchewan. As the name suggests, these fish have fins comprised of bones similar to bones that make up limbs (like in a whale, or seal.) Some of these fish also have the capability to breathe air, having developed "lungs".