rock cod; black-saddled grouper
Refers to the fish species Epinephelus akaara, a type of grouper found in East Asian waters. The name 小豆鱒 is a Japanese common name; it is not a trout despite the 鱒 kanji.
The rock cod is known as a high-class fish.
I found fresh rock cod at the market.
The name 小豆鱒 (azukimasu) literally means 'azuki bean trout', but the fish is a grouper, not a trout. The origin of this name is uncertain; it may refer to the fish's reddish spots resembling azuki beans.