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In this study, we investigated the effects of dietary lipids (DL) on the growth and lipid deposition of steelhead trout (Oncorhynchus mykiss) confined underwater using various equipment. Three diets formulated with 6%, 13%, and 20% DL (F6, F13, and F20) were fed to the fish. Fish (initial weight: 75.01 ± 1.36 g) in each dietary group were randomly cultured in three equipment groups: the control group; the submergence group, in which mesh and airstones were used to keep the experimental fish from the water surface; and the replenisher group, in which an air replenisher and airstones were utilized under the mesh. The results of this 70-day study showed that the growth and crude lipid content of the steelhead trout fish body increased significantly with increasing DL levels. No significant differences were observed in the liver among the different equipment groups, whereas the lipid contents in the muscle and the viscerosomatic index significantly decreased in the submerged group fed F20. The fitted curve analysis showed that the energy expenditure of continuous swimming and the success of replenishing the swim bladder may determine the strategy adopted by trout to cope with negative buoyancy. If the swim bladder was easily replenished, steelhead trout tended to convert excess energy into lipid stored in muscles, thereby reducing body density and maintaining neutral buoyancy. Otherwise, trout must burn lipid in their muscles to ensure energy supply to keep swimming for lift. We concluded that a high-lipid diet compensated for the loss of the energy used in resistance to negative buoyancy, and growth performance of steelhead trout improved.

To examine the growth and immune response of steelhead trout (Oncorhynchus mykiss) under conditions of differing light color, we investigated the effects of different red and blue light color combinations on plasma non-specific immunity, hepatic antioxidant capacity, and GH/IGF-1 axis gene expression in juvenile steelhead trout (initial weight: 34.67 ± 2.69 g). The 16-week trial was set up with six treatments in which light color varied at a constant light intensity of 150 lx: 12 h white light + 12 h dark (12 W), 12 h blue light + 12 h dark (12B), 12 h red light + 12 h dark (12 R), 1.5 h blue light + 9 h red light + 1.5 h blue light + 12 h dark (3B9R), 3 h blue light + 6 h red light + 3 h blue light + 12 h dark (6B6R), total 12 h of blue and red light + 12 h dark (T12BR). The results revealed that the 12B and 3B9R light environments significantly enhanced plasma immunoglobulin M levels in steelhead trout, and that the 3B9R light environment also promoted significant increases in the gene expression of hepatic growth hormone receptor, insulin-like growth factor 1, and insulin-like growth factor-binding protein. The 3B9R light environment was also found enhance the antioxidant capacity of trout by increasing hepatic superoxide dismutase, catalase, and glutathione peroxidase activities. In contrast, trout exposed to the 6B6R light environment showed significant reductions in growth and immune performance, and there were similar reductions in hepatic antioxidant capacity. Furthermore, fish exposed to the 12R light environment were found to be characterized by elevated levels of lipid peroxidation and malondialdehyde, which are indicative of hepatic stress. In addition, we observed that in response to light variation, there were elevations in the activities of glutamic oxaloacetic transaminase and lactic dehydrogenase in the plasma of steelhead trout, thereby indicating an inhibition of cardiomyocyte function. In summary, our findings indicate that a 3B9R light environment simulates the blue-red-blue daily rhythm of light color variation in natural underwater environments, which is beneficial with respect to enhancing the growth and immunity of steelhead trout, and could accordingly be used to provide suitable light conditions in commercial trout production. However, sudden changes in light color should be avoided in the aquaculture of trout.

Transportation is common and necessary in aquaculture practice. A series of physiological changes in fish are caused by transportation stress. The present study investigated the effects of transportation of rainbow trout Onchorhynchus mykiss. Juvenile rainbow trout were placed in plastic bags, and sampled before transportation (P1), two hours after transportation (P2) and 48 h after transportation (P3). The water temperature, dissolved oxygen (DO), ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N) and nitrite nitrogen (NO2–-N) were analyzed. The relative expression of genes involved in stress and immunity (IL-1β, IL-8, TNF-α, LYZⅡ, HSP70 and HSP90), hypoxia tolerance (hif-1α, GLUT-1) and NF-kB pathway related (NF-kB, Ikb and Ikb2) were analyzed by RT-QPCR. In addition, oxidative damage, antioxidant and immune parameters (the activity of malondialdehyde MDA, superoxide dismutase SOD, catalase CAT and total antioxidant capacity T-AOC, acid phosphatase ACP, alkaline phosphatase AKP and total nitric oxide synthase NOS) were determined. The level of DO at P2 point was significantly decreased compared with P1 and P3 point. The NH4+-N concentration was significantly higher than that at P1 and P3. Further, there was a significant increase in HSP70 expression in gill and muscle during transportation. The expression of TNF-α, IL-1 β and IL-8 in gill and IL-1 β and IL-8 in muscle were significantly up regulated during transportation. The HSP70/90, TNF-α, IL-1 β and IL-8 genes can be used as bio-indicators to monitor stress. Moreover, ACP enzyme activity in liver and muscle, AKP in gill and MDA contents in gill and muscle were significantly higher at P2. The activity of NOS and T-AOC in gill was significantly higher at P3, and showed an increasing trend. In general, this study provides basial information of transportation, and will be helpful to choose more suitable conditions for successful transportation of juvenile rainbow trout.