The circulatory system of trout and salmon, all bony fish, share characteristics common to many other animals. Some characteristics are unique. Check out this diagram. What organs are unique to fish? What organs and processes do fist share with other animals?

Most fish, including trout and salmon, breathe through gills located on either side of the pharynx. The gills are feathery filaments containing many capillaries and a large surface area for the exchange of oxygen and carbon dioxide. Trout and salmon breathe through the mouth, pumping water the gill filaments. They exhale through a single opening, the gill slits, which is protected by a gill cover.

Like most complex animals, fish have a closed circulatory system with a heart that pumps blood through the body. The heart consists to two muscular chambers that pump the blood: An atrium and a ventricle. Blood from the body gathers in the atrium, which is then pumped into the ventricle. The ventricle pumps the blood into a muscular vessel called the aorta. Blood goes directly from the aorta to the fine capillary network in the gills, where the exchange of gas takes place. From the gills, the blood travels throughout the body providing tissue and organs with life giving oxygen and removing carbon dioxide. Once the blood has completed its journey through the body, it gathers in a thin-walled sac called the sinus venosus before entering the atrium once again.