Yellow croaker Spanish mackerel has a liver-shaped stomach, which is the testis of male fish, also called fish white.

Some fish have eggs in their bellies, while others have white fish. Those with fish eggs are females, and those with fish white are males. Two pieces of fish white * * *, wrapped in film, taste slightly astringent but delicious after cooking. "Fish white" is the reproductive organ of male fish. It contains a special protein called protamine, which is the simplest alkaline protein in nature.