The main reason is that the fish Lin Yang is serving was just caught, ensuring the absolute best in freshness.
"Mmm, indeed it's not bad." Taking a piece of Yellow Sea Bream into his mouth, Lin Yang nodded as he ate.
In fact, whether it's freshwater or saltwater fish, what you're eating first and foremost is the freshness, which generally can only be guaranteed by a living fish. Even the tastiest fish, once frozen, will have a significantly worse texture.
Well... that isn't to say without exception. For example, large tunas can't be eaten fresh because their muscles are very well-developed. So, they have to be treated like beef, subjected to low-temperature freezing to remove the acids before they can taste good.
However, such fish are the minority. Most fish have white flesh, which doesn't require acid removal, so maintaining their liveliness is critical. Even the most delicious freeze-caught wild fish doesn't taste as good as a living farmed one.