tuna / important commercial fish / many countries by the Mediterranean / specially / Japan.

A. Tuna are important commercial fish in many countries by the Mediterranean, specially in Japan.

B. Tuna that are important commercial fish in many countries by the Mediterranean, specially in Japan.

C. Tuna, they are important commercial fish in many countries by the Mediterranean, specially in Japan.

D. They are, tuna, important commercial fish in many countries by the Mediterranean, specially in Japan.