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

## TL;DR

This study shows that hydrophobic extracts from Solanum trilobatum leaves improve tilapia immunity and disease resistance better than hydrophilic extracts.

## Contribution

The novel finding is that hydrophobic plant fractions are more effective immunostimulants in fish due to better bioavailability of aromatic and steroid compounds.

## Key findings

- HSF improved immune responses like ROS and MPO more effectively than WSF.
- HSF-fed fish showed consistently lower mortality after bacterial challenge.
- HSF contains higher levels of bioavailable aromatic compounds and phytosterols.

## Abstract

Disease outbreaks in fish farms, especially under crowding and confinement, are responsible for causing major economic loss to farmers. This study has been designed to examine the ability of two extracts (water or hexane soluble fraction, WSF or HSF) from the leaves of the plant Solanum trilobatum to enhance the health of tilapia fish. The fish were fed with these extracts incorporated into their diet for 1, 2, or 3 weeks. Results showed that both extracts improved the immune system over time by enhancing globulin level, lysozyme, and anti-protease activity. HSF enhanced key immune responses like reactive oxygen species (ROS) and myeloperoxidase activity (MPO) and led to higher antibody levels than WSF. When the fish were challenged with Aeromonas hydrophila, those fed HSF had lower death rates at all time points, while WSF only helped at certain doses and days. Chemical analysis showed HSF had high levels of aromatic compounds and phytosterols which are likely easier for the fish to absorb. WSF had smaller alcohol and carbonyl compounds, but in lower amounts. Because of better absorption, HSF was more effective at strengthening immunity and protecting fish from disease.

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.