DIFFERENT SIZES OF BUBBLES ON AIR SUPPLY OF RAINBOW TROUT IN SUBMERGED CULTURE SYSTEM

Submerged cage culture represents an effective solution to challenges posed by high temperature, typhoon, and fish lice infection in open sea aquaculture. However, it leads to the adverse effects on physostomous fish like salmon such as gas loss in the swim bladder, slow growth, skeletal deformity, and high mortality. In order to investigate the effects of different bubbles sizes on the growth, behavior, energy budget, antioxidant capacity and body morphology of submerged rainbow trout (Oncorhynchus mykiss), this experiment established five groups with different aquaculture equipments as follows: the control group (without mesh and air supply device), the no-bubble group (adding mesh for isolation) and the three bubble groups (adding mesh for isolation and three kinds of air stone under the mesh for air supplement, with bubble diameter of 1.02, 0.33 and 0.11 cm, respectively). After a 28-day trial, the results showed that the final body weight and specific growth rate of rainbow trout in the large and medium bubble groups were significantly higher than those in the small and no bubble groups. The swim bladder volume and buoyance generated by swim bladders of rainbow trout in the large and medium bubble groups were significantly greater than those in the small and no bubble groups. These indicate that the large and medium bubbles effectively supplemented gas in the swim bladder of rainbow trout and restored its growth. The activities of SOD and CAT of rainbow trout in the bubble group were significantly lower than those in the control group, and MDA and LPO were significantly decreased, indicating that the anti-oxidation system of rainbow trout was damaged by diving stress. However, the IBR_v2 of the antioxidant index of rainbow trout in the large and medium bubble groups was closer to the control group than the small and the non-bubble group, indicating that it could alleviate the negative effects of submerged culture to a certain extent. The body of rainbow trout in the bubble group was more streamlined than that in the control group, with an increased relative area of fin and tail, which may be an improvement measure for rainbow trout to cope with the lack of buoyancy. In conclusion, the large and medium bubbles are more effective in alleviating the negative buoyage of rainbow trout, probably because the large bubbles are more conducive to being swallowed by the fish and compressed to the swim bladder tube.