Chippy Williams, age 10, of Charlotte, North Carolina, for his question:
Do fish have hearts?
When a zoologist examines the body of a strange animal, he knows just where it belongs in his huge system of classifications. This clear cut system is organized according to basic bodily features. One important clue is the heart. The type of heart may be the one feature that determines the group in which an animal belongs.
The amoeba, like many other simple little fellows, has no heart at all. The single cell from which his body is made must carry on all the duties of living. A but¬terfly is a larger, more complex animal with a body made from numerous cells that accom¬plish the chores of living by becoming specialists. Groups of cells are arranged in units called organs which carry on only one or two of the many duties. The different organs work together as a team to carry on the complicated, interrelated living processes of the whole body.
In the body of a sizable animal, all the fixed cells must be provided with food and fuel. It must have systems to bathe and repair them and trash systems to dispose of their waste materials. One of the vital organs, in this busy biological teamwork is a heart. It must circulate oxygen fuel to the assorted cells and bathe them in soothing, nourishing fluid, wash away their waste materials and send the circulating blood stream to be purified and replenished for another round of duties.
This heart may be a rather simple organ. The heart of a butterfly is merely a little tube with branching blood vessels leading through the cells. The body of a fish is more complicated. It has a bony skeleton with a jointed spine and spiky ribs, a skull with a pair of toothy jaws. It has a nervous system linked to keen senses of sight and smell. The fish's survival in the teeming ocean often depends on speed. And his body has a system of smooth, energetic muscles to keep him on the move.
The fish needs a heart to keep this biological system in operation, but it does not have to be as fancy as the super, four chambered heart of a chimpanzee. The fish's heart requires only two chambers to carry out its duties. Naturally, it is connected to the networks of branching blood vessels throughout his fishy body. One set of branches carries used blood to the gills to be purified and replenished with fresh oxygen. Other branches carry fresh blood among the cells, to the liver and kidneys and other organs.
A system of valves in his heart act like faucets to control the flow of blood between the two separate chambers. Used blood gathers into the thin walled auricle chamber. The thick, muscular ventricle chamber contracts with a rhythmical beat to pulse the blood the the gills. The same pulsing beat also pushes the blood stream on its circuit throughout the fish's body.
The fish, of course, has no complex thermostat system. He is a so called cold¬blooded animal, unable to adjust his body temperature. All animal bodies need just .. the right amount of heat to carry on their work. But the poor fish gets hot or cold with the water. He depends upon his surroundings to keep his body in working condition.