Its not the answer of my question. Good day.

Fish play a significant role in ecosystem either in marine or fresh water. It maintains zooplankton/ phytoplankton population by consuming as food, and  serves as prey for higher  trophic level animals.  Besides this fish is exploited partially from ecosystem for human consumption. Fish role is important because it converts phytoplankton/ zooplankton into edible form (fish ) for human consumption, serving as a source for omega-3 and omega-6 fatty acids and protein that promote health of common man.When fish exploitation exceeds optimum level ecosystem balance will be disturbed and common man will be deprived of  essential fatty acids as well as protein source.