In order to meet the demand of salmon market, Chinese scientists and entrepreneur are working on salmon mariculture far offshore in the Yellow Sea, China. A fully submersible ocean farming cage (Deep Blue No 1) was conducted in China since 2016. However, submergence causes loss of air from the swim bladder, leading to negative buoyancy, modified swimming behaviours, and reduced growth and feed utilisation. The objective of this study is to evaluate the response of rainbow trout to the negative buoyancy and gas replenisher in tanks.
Rainbow trout (N=3; initial weight 63.84 g) were distributed to four treatments with different devices (control, mesh, dome & mesh, and airstone & mesh) at a density of 13 fish per tank over a 40-day feeding trial. The mesh in the tank was used to isolate rainbow trout from the water surface to simulate the submerged sea-cage. The gas replenisher is designed as an underwater gas domes or airstone at the bottom of tank. The meshes and gas replenishers treatments were compared with the control group to ensure that gas replenishers can effectively solve the negative buoyancy.
At the end of the trial, the final mean weight ranged between 77.69 and 90.00 g, weight gain varied from 7.09 to 40.51%, survival ranging from 76.92 to 100.00%, and FCR was between 1.33 and 2.43 (Table 1). Results of the study showed the mesh treatment had a significant effect on the growth of rainbow trout. The dome & mesh treatment can successfully eliminated the effect of the mesh. More physiological index will be further analyzed and reported.