Differential Immunostimulatory Effects of Hydrophilic and Hydrophobic Solanum trilobatum Fractions in Tilapia

Plant-derived immunostimulants stimulate the fish immune system, prevent diseases, and reduce economic losses for farmers. This study fed tilapia (Oreochromis mossambicus) either water (WSF) or hexane soluble fraction (HSF) of Solanum trilobatum leaves for 1, 2, or 3 weeks to assess their effects on nonspecific immune responses, antibody response, and disease resistance to bacterial challenge after each feeding period. Both WSF and HSF increased serum globulin levels after 3 weeks and significantly elevated lysozyme and antiprotease activity. WSF increased ROS production after 3 weeks, while HSF had a significant effect after 2 weeks. MPO content increased after 1 week for WSF and after 1, 2, and 3 weeks for HSF. The antibody response was significantly higher in the HSF-fed group across most time points. Challenge with Aeromonas hydrophila showed reduced mortality in fish fed with HSF for 1, 2, and 3 weeks, while WSF only reduced mortality at certain doses after 1 or 3 weeks. GC-MS analysis revealed that HSF contained about 40% aromatic compounds and 11% steroids, mainly phytosterols. In contrast, WSF contained several low molecular weight alcohols and carbonyls, each in proportions of less than 10%. Due to their hydrophobic nature, the aromatic compounds and steroids in HSF are likely more bioavailable, which may explain its superior immunostimulating and disease resistance properties.