The Circulatory System of the Bony Fish
Ardan Huck July 7, 2002

The circulatory system of bony fish consists of three main components: the heart, blood, and blood vessels.

The circulatory system of the bony fish consists of one main circuit, from the heart to the gills, to the cells. The circuit is a "closed system" (it is contained in vessels and a loop).

1. Blood consists of the following (the concentration of these products is controlled through "osmosis" which controls the amount of fluid):

A. Red blood cells to transport oxygen to the cells in the fish and transport carbon dioxide away from the cells. Red blood cells are high in hemoglobin which is high in iron. The iron binds with the oxygen for transport. Red blood cells are produced in the spleen, kidney and in the bones according to some authors.

B. White blood cells are made up of several types and are discussed more in the topic about "The Immune System of the Bony Fish."

C. Platelets help with coagulation of the blood to stop bleeding. There are also other coagulation components.

D. Plasma is the liquid part of the blood to suspend the other components of the blood with in it, including food for the cells (broken down into various components by the digestive system), hormones, and waste products from the cells to the liver and kidneys.

Fishes' blood is approximately 2% of their body weight, compared to 10% in humans.

2. Blood vessels consist of:

A. Arteries carry blood from the heart to the gills and then to the rest of the organs and body tissues. The oxygenation process in the gills will be discussed in another topic about the gills and how they work.

B. From the arteries the blood goes into smaller vessels called capillaries and then into fluid surrounding the cells called “interstitial space” (around cells).

C. Veins carry carbon dioxide and waste products away from the cells, back to the heart.

3. The heart of the bony fish is unique. It only has two chambers, compared to 4 chambers in the human heart (3 chambers in an amphibian).

Blood flows back to the heart via veins. Two main veins are the "Hepatic veins" (from the liver) and the ducts of "Cuviar" (the main veins from the rest of the body). These join together into one larger vein called the "Sinus venosus" (this has a large muscle around it and some consider it another chamber). It then goes through the first valve of the heart (to keep blood from flowing backward) called the "sinuatrial valve." Blood then flows into the first chamber of the heart called the "atrium" (it is the smaller of the two chambers because it does not have to do as much work as the other chamber).

The blood then flows through another valve called the "atrioventricular" valve (named so because it is between the atrium and the ventricle). Blood continues into the largest chamber of the heart called the "ventricle." Blood then goes through one more valve and into the main artery called the "ventral aorta." Here is where the bony fish differs from the shark. In the shark there are more muscles and valves in this artery; they are absent in bony fish. In the bony fish there is another large muscle around the ventral aorta called the "bulbous ateriosus." Some call this a fourth chamber.

  • "SeaLife" by Marc Dando and Michael Burchet, 1996
  • "World Book Encyclopedia" by World Book, Inc., 1990
  • "Anatomy and Physiology" by Anthony and Thibodeau, 1983

Internet Resources:

   Website designed by: © 2001-2004, All Rights Reserved.