B.G. Kapoor & Ewa Kulczykowska 
Biological Clock in Fish [PDF ebook] 

Each organism has its own internal biological clock, which is reset by environmental cues (Zeitgebers), thus keeping it synchronized with the external environment. It is a chemically based oscillating system within cells, relying on molecular feedback loops. Circadian biological clocks exist in most organisms.What is so special about the clock in f