and Circulatory System
Perch (Perca flavescens)
Taxonomy and Evolution
- Kingdom - Animalia
- Phylum - Chordata
- Class - Actinopterygii
- Order - perciformes
- Family - Percidae
- Genus - Perca
True perch have "rough" or ctenoid scales. On the anterior side of the head are the maxilla and lower mandible for the mouth, a pair of nostrils, and two lidless eyes. On the posterior sides are the opercula which protect the gills, and the lateral line system, which is sensitive to vibrations in the water. They have paired pectoral and pelvic fins, and two dorsal fins, the first one spiny and the second soft.
Closed Circulatory System
- Blood collected from throughout the fish's body enters a thin-walled receiving chamber, the atrium.
- As the heart relaxes, the blood passes through a valve into the thick-walled, muscular ventricle.
- Contraction of the ventricle forces the blood into the capillary networks of the gills where gas exchange occurs.
- The blood then passes on to the capillary networks that supply the rest of the body where exchanges with the tissues occur.
- Then the blood returns to the atrium