The Heart
Because these perch you are using are not injected you will only exanime the heart of this aquatic chordate. To expose the pericardial (heart) cavity extend the ventral incision approximately 2 cm anterior to the pelvic fins. Extend this incision dorsally under the gills to the lateral line. The pericardial membrane should adhere to this flap of body wall you have cut. Gently free the membrane as you raise the cut flap.
You will notice a heavy membrane separating the pericardial and abdominal cavities. It is termed the transverse septum. The fish heart consists of four distinct parts (Figure 8 and 9). Posterior to anterior (in the same direction as blood flow) these are the sinus venosus, atrium, ventricle and bulbus arteriosus. These parts are not arranged in a straight line in the adult fish, but have folded over one another to produce a S-shaped organ. The top of the S, the sinus venosus, receives blood from two common cardinal veins and the hepatic sinus. The sinus venosus is thin walled and opens directly into the atrium. The atrium is equivalent to the paired atria of higher vertebrates. It is thicker walled and larger than the sinus venosus. The ventricle itself is a thick muscular structure. Like the atrium, it has a single internal chamber. Backflow of blood from the ventricle during contraction is prevented by a valve. The last portion of the perch heart is the bulbus arteriosus. The bulbus arteriosus is really an enlarged, very muscular portion of the ventral aorta, the vessel in which blood flows away from the heart and toward the gills. Backflow of blood from the bulbus arteriosus is also prevented by the presence of valves. Figure 10 traces the flow of blood through the perch heart.
FIGURE 8 HEART OF THE PERCH - VENTRAL VEIW
FIGURE 9 HEART OF THE PERCH - RIGHT LATERAL VIEW
FIGURE 10: PATH OF BLOOD FLOW THROUGH PERCH HEART
