*3.2. Parameters of Culture Environment*

The daily average dissolved oxygen, temperature, salinity, pH, and weekly average total ammonia nitrogen of water in the ship and cage are recorded in Figure 3. During the experiment, the temperature of the cage increased steadily and kept at a relatively high level on the whole, ranging from 23.3 to 28.5 ◦C, 26.6 ◦C on average. The water temperature of the ship remained stable for the first 5 weeks, below the cage temperature. After the ship was moved to the sea area of Qingdao due to the typhoon, the temperature increased significantly and remained until the end of the test, similar to that of the cage group. The temperature of water in ship was maintained between 21.5 and 28.5 ◦C, with an average of 25.5 ◦C during culturing (Figure 3A). In the cage group, the salinity did not change significantly during the 8-week experiment, staying at 25–30‰, with an average of 29.4‰. The salinity of the ship increased steadily in the first 6 weeks from 20.7‰ to 29.1‰, which was lower than the cage during this period. It remained stable at around 30‰ for the next 2 weeks until the experiment was completed, when the salinity was similar to that of the cage group. The whole process was maintained between 20.7 and 31.8‰, with an average of 26.9‰ (Figure 3B). In addition, the level of dissolved oxygen on the ship was higher than that in the cage most of the time (Figure 3C). There was a similar pH between the two groups during the trial (Figure 3D). The ammonia nitrogen concentration of the two groups

remained at a low level during the experiment, both of which were lower than 0.08 mg/L (Figure 3E). In this trial, environmental conditions in the ship group were harsh, including higher waves and stronger winds (Supplemental Data, Figure S1).

**Figure 3.** Comparison of water temperature (**A**), salinity (**B**), dissolved oxygen (**C**), pH (**D**), and ammonia nitrogen (**E**) in the ship and cages throughout the experiment period.

#### *3.3. Total Number of Bacteria and Vibrio in Water*

The total number of bacteria and vibrio in the tank of the ship were detected by the plate method, which remained stable at a low level and tended to increase slightly with the increase of breeding time. Still, there was no significant difference (Figure 4). The total number of bacteria was maintained at 1.2 ∗ <sup>10</sup>3–1.6 ∗ <sup>10</sup><sup>3</sup> CFU/mL, and the total number of vibrio was maintained at 1.2 ∗ <sup>10</sup>2–1.8 ∗ <sup>10</sup><sup>2</sup> CFU/mL.

**Figure 4.** Changes in the total number of bacteria and vibrio in the fish tank of offshore aquaculture ship throughout the experiment period. Bars with different superscripts on the same microorganism are statistically different (*p* < 0.05, n = 3).
