Among immunostimulants used in aquaculture, herbal is promising due to their propensities to improve growth performance, fish immunity, and their antimicrobial properties, as they are good alternatives to chemical treatments and antibiotics. As medicinal herbs are eco-friendly, cost effective, have minimal side effects, and they have gained attention in the prevention and treatment of fish diseases. Plant-derived compounds are reported to stimulate fish immunity due to the presence of many bioactive secondary metabolites, and studies comprising gene expression, proteomics, and metabolomics have improved the understanding of the effects that herbal compounds can have on fish immune status. The current review summarizes findings pertaining to the role of plant-derived compounds with immunostimulant properties in fish.