paul greenberg, good to have you on the program, sir. >> good to be here. tavis: given all that we are hearing about the oil spill and what it is doing to lives of the fish that we love to eat. why a book called "four fish"? why these four fish? >> well, when you look around at all the land mammals that we eat. four we domesticated. cows, pigs, sheep and goats. you look at all the birds, turkeys, chickens, ducks and geese. where we're at with fish now, we have huge problems with overfishing. fish farming is the largest production of food production now. tavis: and they are? >> they are salmon, sea bass, that applies to a lot of fish but in this case, the european sea bass and cod fish and tuna. tavis: you used a phrase a moment ago. overfishing. define that for me. >> well, overfishing is a relatively new concept that has come out. it means that you're catching more fish than the ecosystem can replace over time. generally, a lot of times it is considered when you go over 40% of the -- excuse me, over 60% of the historical population of any one species of fi