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 (<i>Oreochromis mossambicus</i>) either water (WSF) or hexane soluble fraction (HSF) of <i>Solanum trilobatum</i> 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 <i>Aeromonas hydrophila</i> 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.