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. 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 x 10(6) mm(-3), 5.54 +/- 0.21 x 10(3) 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.