Dietary Pot Marigold (Calendula Officinalis) Extract Improved the Growth Performance, Expression of Digestive Enzymes, Antioxidant Enzymes and Immune-Related Genes in Rainbow Trout (Oncorhynchus Mykiss)

Abstract

The current study was designed to test the dietary pot marigold (Calendula officinalis) extract on growth performance and expression of genes related to digestive enzymes, antioxidant capacity and immune system in rainbow trout (Oncorhynchus mykiss) for 60 days. 240 fish (initial weight 15.33 +/- 0.26 g) were randomly divided into 12 tanks (volume of 200 L, 20 fish per tank, in triplicates). Experimental diets were supplemented with 0 (C), 0.5 (PM05), 1 (PM1) and 2 (PM2) g kg(-1) pot marigold extract. Fish were fed ad libitum until the fish reached apparent satiation with nutritionally balanced diets (48% crude protein and 18% crude lipid) three times (08.00 am, 1.00 pm and 6.00 pm) daily. At the end of the study, the fish were individually weighed to measure growth parameters, including final weight (FW), weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER), and feed conversion ratio (FCR). For gene expression analyses, the liver (antioxidant and non-specific immune parameters) and intestinal tissues (digestion) were sampled from fish (3 from each tank). Results showed that PM treatments had greater growth indices in comparison to the C group. (P < 0.05). The highest FW, WG, SGR and PER values were recorded in the PM1 treatment (P < 0.05). Similarly, the lowest, i.e. best FCR levels were obtained in the PM1 group (P < 0.05). Intestinal trypsin expression levels were significantly higher in the PM05 and PM1 treatments than in the C group, with the highest expression in the PM1 treatment (P < 0.05). Lipase expression reached the highest level in the PM1 treatment, while amylase was upregulated in all PM treatments compared to the C group (P < 0.05). Hepatic superoxide dismutase (SOD) expression levels were increased in the PM05 group, followed by PM1 and PM2 treatments (P < 0.05). Also, catalase (CAT) expression values were higher in the treatment groups than in the C group (P < 0.05). The glutathione peroxidase (GPX) expression level in the PM2 treatment was increased compared to the C group, while GPX in the PM05 and PM1 groups was significantly lower than in the C group (P < 0.05). Expression levels of interleukin-1 beta (IL-1 beta), tumour necrosis factor (TNF-alpha) and interleukin 8 (IL-8) genes relating to immunity exhibited overexpression in treatment groups compared to the C group. In conclusion, it can be concluded that diets supplemented with pot marigold extract, especially at 1 g kg(-1) level, can promote healthy growth for rainbow trout.