Humans are adapted for life on land only, we wouldn’t survive in water more than few minutes. Yet without life in aquatic systems, seas, rivers and lakes, many of us wouldn’t be a life at all and even vanished away longtime ago. But do we understand the secrets of life in fresh, brackish and marine water systems, from where fish (small and big) get their food, do fish drink water, if so how do food-chains look like in aquatic systems, does life exist in surface sediments. Do fish sleep, and while swimming how do fish navigate between stones, corals, identify there way, survive the dark environments in deep regions and at nights?  Do fish get sick, have diseases and eventually die, if so why and how?

https://www.youtube.com/watch?v=1R5T9xEiOT0&feature=youtu.be