I just watched a programme 'Preserve Our Planet' on National Geographic Channel in which they showed how the well being of fish is linked to our planet's well being.
First they showed the link between disappearing animals in the forests of Ghana to the depleting fish population in its sea waters. This has also caused the population of baboons to increase manifold thus creating havoc in the forest ecosystem there.
Later the focus shifted to a mysterious phenomenon in a small stretch of coastal Namibia. A nasty smell engulfs the coast with the sea waters changing colours and finally hordes and hordes of dead fish washing ashore. A marine biologist is intrigued by the phenomenon and choses to look deeper into the source while others turn a blind eye. She discovers that phytoplanktons in the sea waters, when dead, fall to the sea bed. Over years a thick layer of these dead phytoplankton is formed on the sea bed. This layer decays releasing hydrogen sulphide along with methane. When the concentration of methane has reached a critical level, the layer of dead planktons burst like a bomb releasing methane and H2S gas. The H2S gas suffocates the nearby shoals of fish, also the sulphur changes the water colour. One who has studied chemistry will obviously know how nasty is the smell of hydrogen sulphide - like that of rotting eggs. The resutling release of methane contributes heavily towards global warming.
Well, fish feed on phytoplanktons. Since the fish population is dwindling, phytoplanktons thrive in large numbers and litter the sea bed, when dead. This is observed in Namibia because the country is one among the top most fishing countries in the world. It won't be long before similar marine tragedies occur elsewhere if mindless fishing is not checked in time.
Moral of the story - Protect fish to protect our planet, our home.