*2.3. Determination of Water Quality*

During the trophic period, water temperature, salinity, dissolved oxygen, and pH were measured by an automated water quality analyzer (YSI-556, Beverly, MA, USA) once a day. The total ammonia nitrogen was measured once a week using a hash water quality detector (NA8000, Beverly, MA, USA).

The total number of bacteria and vibrio in the water of the tank in ship was measured by the plate counting method [20] and tested once a week. The TSA and TCBS (Sangon Biotech, Co., Ltd., Shanghai, China) was selected as medium. Water samples were collected in the culture tanks, diluted 100 times with sterile seawater, and then coated with 100 μL on the medium and placed at 28 ◦C for 24 h. Finally, the plate was observed and counted.

#### *2.4. Experimental Sampling*

For the period of the test, the number of dead fish and daily food intake of large yellow croaker of two groups per day were recorded to count the survival rate and the feed conversion ratio. A total of thirty fish were randomly collected from each tank in the ship every 15 days, and their body weight and body length were measured. At the same time, their visceral fat was dissected and weighed. After the experiment, large yellow croaker of two groups was starved for 24 h, thirty fish were randomly collected from each tank and cage to measure body weight, body length, and weight of visceral fat. Then, ten fish in each tank and cage were obtained with skinless muscle samples, which were placed at −80 ◦C for nutrient detection.
