Dietary effect of liquorice (Glycyrrhiza glabra) aqueous extract powder on some skin mucus immune parameters and protein pattern in juvenile rainbow trout (Oncorhynchus mykiss)

Today, the use of herbal supplements based on medicinal plants in aquatic nutrition has become widespread due to their high effectiveness, availability, and environmental friendliness. Accordingly, the effects of liquorice extract powder in improving some skin mucus immune parameters of rainbow trout were studied. 270 pieces of juveniles with an average weight of 9.46±0.11 g were distributed in 15 plastic tanks with 18 fish per tank density and after two week of adaptation to the new environmental conditions , they were fed with different levels of liquorice aqueous roots extract powder including 0 (control), 0.5, 1, 2, and 3 % for 56 days. The skin mucosal lysozyme activity was measured manually and other mucosal immune parameters were evaluated by a biochemical autoanalyzer. Also, the skin mucus protein pattern was performed by vertical electrophoresis of sodium dodecyl sulfate polyacrylamide gel (SDS-PAGE). The results showed that lysozyme activity (15.94±0.51 U mL/min), mucosal total protein content (4.87±0.19 mg/dl), total immunoglobulin content (4.89±0.14 U/L) and activity of alkaline phosphatase enzyme (42.0±0.89 U/L) of mucus in fish fed with 2 % of liquorice treatment was higher than other experimental groups (P<0.05). Also, the results of skin mucus SDS-PAGE confirmed the existence of significant differences between mucosal protein units in different treatments (p<0.05). The experimental results showed that the use of liquorice as a medicinal plant, especially at the level of 2%, can have positive effects on safety indices and protein patterns of rainbow trout skin mucus.