The purpose of this study was to investigate the effect of different levels of nanoliposome-coated astaxanthin (NA) on growth performance, body proximate composition, liver enzyme activities and pigmentation in rainbow trout (Oncorhynchus mykiss). Groups of fish weighing 31 ± 2 g each in three replicates (30 fish per replicate) were fed with 0, 25, 50, 75 and 100 mg/kg nanoliposome-coated astaxanthin for 60 days. At the end of the experiment, growth performance including final weight, weight gain (WG), feed conversion ratio (FCR), specific growth rate (SGR), survival rate (SR), daily growth rate and condition factor (CF), body crude protein, fat, ash and moisture, liver enzymes (ALT and ALP) and pigmentation (skin and muscle carotenoids and muscle astaxanthin) were measured. The results showed that the addition of NA had a significant effect on growth indices (p < 0.05). The highest final body weight (FBW) (101.46 ± 4.46 g) was related 75 mg/kg NA, and the lowest FBW (93.10 ± 0.96 and 91.98 ± 4.08 g) was seen in control and 100 mg/kg NA respectively (p < 0.05). Also, the highest amounts of protein and ash were measured in 50 and 75 mg/kg NA treatments, while the lowest levels of these occurred in control and 100 mg/kg NA. The highest amount of serum ALT and ALP enzymes was in 100 mg/ kg nanoliposome-coated astaxanthin treatment, and the lowest amount of ALT enzyme was in 50 mg/kg treatment. Also, the lowest amount of ALP enzyme was obtained in control treatment. The concentration of carotenoids in skin and fillet and fillet astaxanthin increased significantly by adding nanoliposome-coated astaxanthin to the diet (p < 0.05). The highest carotenoid quantity of skin and fillet and astaxanthin fillet was observed in fish fed 75 mg/kg nanoliposome-coated astaxanthin and the lowest amount in the control group. These results suggest that the incorporation of nanoliposome-coated astaxanthin into rainbow trout diet at the level of 75 mg/kg can have a positive effect on growth indices, reduced liver enzyme activity and improved skin and fillet pigmentation.

In recent years, chitosan has gained considerable attention due to its favorable properties such as excellent biocompatibility and biodegradability for which it can be used as a health supplement for delivering bioactive compounds in the food industry and nutrition. In the present study, the effect of nanochitosans coated with folic acid (FA) was considered on the growth performance, hematological parameters, antioxidant status, and serum immune responses of rainbow trout (Oncorhynchus mykiss) fingerlings. Graded levels of FA-coated nanochitosan (0, 0.1, 0.25, 0.5, and 1 mg kg−1 diet) were added to the basal diet, and each experimental diet was fed to three groups of fish with an approximate weight of 31 g for 8 weeks. The experimental study demonstrated that dietary FA-coated nanochitosan significantly (P &lt; 0.05) improved the weight gain ration (WGR), specific growth rate (SGR), and feed conversion ratio (FCR) of fish at the end of the feeding trial. There were also linearly increasing trends in red blood cells (RBCs), white blood cells (WBCs), hemoglobin (Hb), and hematocrit (Hct) of fish fed with increasing dietary chitosan/FA levels, whereas no significant difference was recorded in differential leukocyte count of fish among the treatments. In case of antioxidant responses, fish fed diet supplemented with 0.50 mg kg−1 FA-coated nanochitosan had the highest CAT and SOD activities, while the maximum activity of GPX was found in fish fed diet supplemented with 1.00 mg kg−1 FA-coated nanochitosan. Malondialdehyde activity also reached the lowest value in fish fed with 1.00 mg kg−1 FA-coated nanochitosan-supplemented diet (P &lt; 0.05). Measured immune responses showed a linear augmentation in lysozyme activity (LA) with increasing dietary FA-coated nanochitosan, while linearly and quadratically increasing trends were recorded in immunoglobulin M (IgM) content as well as complement component C3 and C4 activities by increasing the supplementation of nanochitosan coated with FA (P &lt; 0.05). Findings of the current study illustrated the positive effect of dietary FA-coated nanochitosan as a promising compound on improving the growth performance, feed utilization, antioxidant status, and immune responses of rainbow trout.

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