One of the reasons these fish were able to survive in the manor was because there were very few people around, but the most important reason was because of the trees. Although the fire fish were very picky, the roots of this tree was one of things they eat. Since the trees were large, their hairy roots were long enough to reach into the ditch, becoming food for the fish. However, during the winters, a lot of the fish would still die, either because of the cold or because the trees didn't provide enough nutrients. Only a few fish had managed to survive.
Because of the difficulty of raising fire fish, not many merchants were able to sell this fish even though they were worth a lot of money. A single fire fish had a minimum price of two gold coins. Not many people could afford this price. And even if you could afford them, any fire fish will go directly to royalty or nobility.
If oil fruits and bamboo rice were one of the favorite foods of commoners, then fire fish were one of the favorite foods of the aristocracy. So no matter how much fire fish you had, you didn't have to worry about no one buying it.
Zhao didn't quite know this, but Meirin knew. Fire fish would make them money faster than selling radishes or oil from the oil fruits.
It was because she understood this that Meirin was so happy that the fire fish could be raised inside the space. She had only heard of a few places on the Continent that could raise fire fish, and they were able to make a fortune. The previous owner of the manor probably tried to make his own fortune off of these small fire fish, but then gave up when he couldn't raise enough.
Looking at these fire fish in the hot springs, Meirin felt happy. "This is really great! As long as we raise these fire fish, we won't have to worry about money."