Explore the intricacies of the fish circulatory system in this comprehensive biology lecture designed for NEET 2021, GCSE, and IGCSE students. Delve into the unique single-circuit blood flow and two-chambered heart structure of fish, consisting of one atrium and one ventricle. Understand the processes of gill circulation and systemic circulation, and learn how this unidirectional blood flow creates an oxygen gradient throughout the fish's body. Examine the limitations this system imposes on oxygen distribution and its impact on the fish's overall metabolic capacity. Gain insights into key components such as the ventral aorta, gills, capillaries, and specialized chambers, providing a thorough foundation for advanced biology studies and examinations.