Why was the rearing of marine species in tank aquaculture so difficult before yonathan zohar figured out how to do it?

I believe this problem has the following choices:

a. It was hard to get the fish to breed and produce offspring for the aquaculturist to raise.

b. Because the fish were stressed in tanks, they required much more food, reducing the profitability of rearing the fish this way.

c. The fish had to be raised in a community with several species of fish in the same tank, and they would attack and eat each other.

d. Marine fish are more aggressive than their freshwater relatives and they tended to fight a lot, often killing some of the other fish in the tank.

The correct answer is:

c. The fish had to be raised in a community with several species of fish in the same tank, and they would attack and eat each other.