The structure and function of the different fins of the rainbow trout, Oncorhynchus mykissThe rainbow trout, belonging to the family Salmonidae, class Actinopterygii (ray-finned fish), inhabits cold streams and rivers and lakes of North America. Those that live in lakes have silvery scales, except those on their backs which are dark green. They are covered with dark spots that usually do not extend beyond the lateral line. The lateral line is a line of sensory organs found on the side of the rainbow trout. It makes it possible to detect the vibrations (and therefore the movements) of the water around it. A pinkish-red band often extends the entire length of the lateral line. The shape of the rainbow trout is a characteristic shape that is not uncommon compared to that of the salmon. (Guidekenairriver.com)Fish fins evolved about 500 million years ago. A fin is a thin appendage attached to an organism's body that causes either propulsion, stabilization, or the ability to steer and brake. The median caudal, dorsal and anal fins are possessed by most fish species. Rainbow trout have six different types of fins: an anal fin, an adipose fin, a dorsal fin, a caudal fin, a pair of pelvic fins, and a pair of pectoral fins. The anal fin is located between the anus and the tail. fin, on the ventral surface of the fish. In rainbow trout, the anal fin is lined with a black margin. This is one of the characteristics of the fish that allows it to be identified. Its function is to stabilize the fish while it swims. Since the dorsal fins are located above the rolling axis of the rainbow trout, the movement of the dorsal fins would cause the fish to roll while swimming without the anal fin counteracting this movement and stabilizing the fish. (Journal of experimental Biology).The dorsa...... middle of paper ......s in the water, as well as a rapid change of pace and direction. Again, this is to escape predation. The pectoral fins are located just behind the operculum – this is the flap of skin that covers the gill slit. When swimming at a constant, steady speed, the rainbow trout's pectoral fins are pressed against its body. However, they are then stretched perpendicular to the body when the fish is hovering in the water, spinning at slow speeds, and are used to abruptly stop the fish when it is moving at fast speeds. Rainbow trout are capable of rotating these pectoral fins over a range of 30 degrees, allowing both hovering and braking sculling. (Drucker EG, Lauder GV, 2003). Evolution took millions of years (500 million) for rainbow trout to develop the fins they have today, each serving a specific purpose involved in the fish's locomotion and stability..