Effects of Ethoxyquin and Lycopene Supplementation on the Growth Performance and Antioxidant Capacity of Rainbow Trout (Oncorhynchus mykiss) Fed Rubber Seed Oil-based Diet

Purpose This experiment was conducted to study the effects of different antioxidants supplementation (ethoxyquin or lycopene) on growth performance, lipoprotein level and antioxidant capacity of rainbow trout (Oncorhynchus mykiss) fed rubber seed oil-based diet, and thereby to select the suitable antioxidant for rainbow trout diets.

Methods Three isoproteic and isolipidic experimental diets were formulated with adding 0.02% ethoxyquin (EQ) or 0.02% lycopene (LCP) or without to rubber seed oil-based diet. The feeding trial lasted for 8 weeks.

Results (1) Dietary supplementation with EQ or LCP generally increased the weight gain and daily growth coefficient although no significant differences were observed. Dietary supplementation with EQ or LCP generally reduced the feed coefficient ratio and improved protein efficiency ratio. Furthermore, the growth performance and feed utilization of fish fed LCP diet were better than those of fish fed EQ diet. (2) Dietary supplementation with EQ generally increased the pepsin activity. However, dietary supplementation with LCP generally reduced the hepatic pepsin and the disaccharidase activities, but no significant differences in the intestine trypsin, amylase, disaccharidase activities, and hepatic trypsin and amylase activities were found among the dietary treatments. (3) Dietary supplementation with EQ generally increased the serum total cholesterol (TC) level; whereas dietary supplementation with EQ generally reduced the serum TC and low density lipoprotein cholesterin levels. (4) Dietary supplementation with EQ or LCP generally improved the plasma total antioxidant capacity, lysozyme, glutathione peroxidase activities and hepatic glutathione reductase activities, whereas those enzymes activities were higher in fish fed LCP diet compared to fish fed EQ diet. Dietary supplementation with EQ or LCP generally reduced the plasma malonaldehyde (MDA) level.

Conclusions Whereas, the plasma MDA level was lower in fish fed LCP diet compared to fish fed EQ diet. The results indicated that dietary supplementation with EQ or LCP may improve the growth, feed utilization ratio and antioxidant capacity of rainbow trout and LCP is a suitable antioxidant for rainbow trout diet.