Hello cherimoya_kid, my current position is yes, fish is good, but because of the reality which humankind has created we must be responsible with how we enjoy it. Heavy metal and chemical pollution in the oceans is common knowledge. Of course you can reduce the impact by eating certain fish i.e. smaller, fattier, farther from land, etc. But the fact is oceans and their denizens are contaminated and suffering more every day.
Industries pollute with methyl-mercury, arsenic, and other heavy metals. Chemical runoff and PCB’s are infecting water systems. Plastics, oil spills, and shipping are also contaminating sea life, and the pièce de résistance, giant manmade continents of floating garbage and waste have emerged. Of all the things we’ve lost from the primal world, it is the oceans and waters which life itself depends on, which are the saddest losses.
Only a few hundred years ago the oceans were immense azure jewels of beauty and bounty. Here in eastern Canada the early explorers’ ships would frequently run aground upon schools of millions of fish, so plentiful were the fish in those days. It would be wonderful to go swimming and fishing in oceans and rivers which are clean, healthy, and sanguine with life.
Of course there is always hope: through education, activism, and legislation our societies can steer a course to restore our marine systems. As CitrusHigh mentioned, it will take sacrifice, discipline, and good managment on a global level, but having our oceans healthy and sustainable is worth it indeed.