Effects of dietary nanoliposome-coated astaxanthin on haematological parameters, immune responses and the antioxidant status of rainbow trout (Oncorhynchus mykiss).

BACKGROUND: Astaxanthin is the most prevalent carotenoid in the marine environment and is widely used as an additive in formulated aquafeeds. OBJECTIVES: A 60-day feeding trial was conducted to consider the effect of dietary nanoliposome-coated astaxanthin (NA) on haematological parameters, serum antioxidant activities and immune responses of rainbow trout, Oncorhynchus mykiss. METHODS: A total of 450 healthy fish weighing 31.00 ± 2.09 g were randomly assigned in triplicate (30 fish per replicate) to 5 dietary treatments: 0 (control), 25.00, 50.00, 75.00, and 100.00 mg kg-1 NA. RESULTS: Fish fed the diet supplemented with 50.00 mg kg-1 NA exhibited the highest values of red blood cells, white blood cells, haemoglobin and haematocrit of 1.64 ± 0.01 × 106 mm-3, 5.54 ± 0.21 × 103 mm-3, 8.73 ± 0.24 g dL-1 and 46.67% ± 0.88%, respectively, which were significantly higher than those fed the basal diet (p < 0.05). The lowest and highest percentages of lymphocytes (67.67% ± 0.33%) and neutrophils (27.33% ± 1.20%) were also obtained in fish fed 50.00 mg kg-1 NA compared to those fed the basal diet (p < 0.05). Fish receiving diet supplemented with 50.00 mg kg-1 NA revealed the highest serum activity in superoxide dismutase, catalase, glutathione peroxidase, lysozyme and alternative complement and the lowest level of total cholesterol, cortisol, aspartate aminotransferase and alanine aminotransferase than fish receiving the basal diet (p < 0.05). Serum immunoglobulin (Ig) and ACH50 contents significantly increased with increasing dietary NA supplementation to the highest values of 43.17 ± 1.46 and 293.33 ± 2.03 U mL-1, respectively, in fish fed diet supplemented with 50 mg kg-1 NA (p < 0.05). CONCLUSIONS: Supplementation of NA in rainbow trout diet at 50 mg kg-1 exhibited a positive effect on haematological parameters, antioxidant capacity and immune responses. Administration of such dosage can enhance rainbow trout immune responses against unfavourable or stressful conditions, for example disease outbreaks, hypoxic condition, thermal stress and sudden osmotic fluctuations, which usually happen in an intensive culture system.

Dietary supplementation with dandelion (Taraxacum officinale) flower extract provides immunostimulation and resistance against Streptococcus iniae infection in rainbow trout (Oncorhynchusmykiss).

Dandelion flower is a well-known phytomedicine due to its therapeutic effects on dyspepsia, bile duct disorders, spleen and liver complaints, and inflammatory diseases. This study aimed to assess the effect of dietary dandelion flower extract (DFE) on skin mucosal and humoral immunity, immune-related gene expression, and disease resistance in rainbow trout. The fingerlings (N = 300, 20.1 ± 0.9 g) were randomly assigned to 15 tanks and fed with different levels of DEF including 0 (control), 1, 2, 3, and 4 g/kg for 56 days. At the end of the trial, the total leukocyte and lymphocyte counts were significantly enhanced in DFE-added groups compared to the control group. Complement components, immunoglobulin M, total protein, and lysozyme showed significantly higher values in the fish treated with dietary DFE at 3 g/kg than others (P < 0.05). The enzymatic activities of the skin mucus samples in the fish fed dietary levels of DFE were significantly higher than the control fish. Skin mucus protein was also improved significantly in 2 and 3 g/kg DFE compared to others. The transcription levels of interleukin-1ß and interleukin-6 genes were up-regulated in the fish fed with 3 and 4 g/kg DFE. Interleukin-8 and lysozyme gene expression levels were elevated in 3 g/kg DFE group compared to the control group. Fish mortality after challenging with Streptococcus iniae was significantly reduced from 43.33% in the control group to 73.33% in 3 g/kg DFE group. This study confirmed the beneficial effects of DFE as an immunostimulant in rainbow trout diet and the recommended dose of DFE is 2.49-2.74 g/kg based on the polynomial regression models.