Combined effects of dietary licorice (Glycyrrhiza glabra) and ginger (Zingiber officinale) on growth performance, intestinal and hepatic health, antioxidant status, and gut microbiota composition in grey mullet (Liza ramada)

Abstract

Licorice ( Glycyrrhiza glabra ) and ginger ( Zingiber officinale ) are phytogenic feed additives with well-documented antioxidant, antimicrobial, and immunostimulatory properties; however, their combined effects in grey mullet ( Liza ramada ) remain unexplored. This trial evaluated the individual and combined effects of these additives on growth, intestinal and hepatic health, antioxidant defense, immunity, and gut microbiota of L. ramada (n = 360, initial mean weight ± SE = 35.15 ± 0.26 g). A 60-day feeding trial was conducted with four dietary treatments (n = 3 replicates; 30 fish per replicate): basal diet (D1; control), licorice (4 g/kg; D2), ginger (10 g/kg; D3), or their combination (2 g/kg licorice + 5 g/kg ginger; D4). All diets were isonitrogenous (31.27 ± 0.19% crude protein) and isolipidic (8.50 ± 0.14% crude lipid). The combined supplementation (D4) significantly ( P < 0.05) improved final body weight, weight gain percentage, specific growth rate, and feed conversion ratio compared to the control and single-supplemented groups. Gastrointestinal enzyme functions (lipase and protease) demonstrated significant enhancement in all supplemented groups compared to the control, with the most pronounced effects in D4. Histological analysis revealed increased intestinal villi length, surface area, and goblet cell count, alongside well-organized hepatic parenchyma and increased glycogen deposition in D4. Biochemical assessments showed elevated total protein and globulin levels with no adverse consequences on glucose or liver and kidney health signs. Dietary supplementation increased lysozyme level, inhibition of Streptococcus agalactiae , and nitroblue tetrazolium (NBT) reduction, with the combined group (D4) showing the maximum levels ( P < 0.05). Antioxidant responses were superior in D4, with increased superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) capacities and reduced malondialdehyde (MDA) ( P < 0.05). Furthermore, gut microbiota analysis demonstrated significant reductions in pathogenic bacteria (including Escherichia coli , Salmonella sp., Vibrio sp., and Staphylococcus sp.) and significant enhancement of acid-fermentative bacteria in all supplemented groups, with the most pronounced effects in D4. These findings underscore the potential of combining licorice (2 g/kg diet) and ginger (5 g/kg diet) as natural feed additives to promote mullet growth, health, and aquaculture sustainability.