Gills of healthy fishes are their lifeline to meet the challenges arising from their changing environment: oxygen gradient, alkalinity, temperature fluctuations and the added pollutants. The diverse and ever changing aquatic environment has a major impact on the organization of various organ-systems of fishes. This book contains seventeen chapters covering bony fishes which are focal to the current study. The chapters primarily cover fish respiration but also include osmoregulation, these being the two main functions of gills. Concurrently, cardiorespiratory synchronization has been well addressed.