As Mediterranean marine fish farming matures, research is increasingly exploring functional nutrition as a tool to strengthen preventive health management. A study published in Fish Physiology and Biochemistry has evaluated the use of plant extracts incorporated into feed as immunostimulants in gilthead seabream (Sparus aurata), with particularly relevant results for nettle extract (Urtica dioica).
The study analysed the effects of different doses of ethanolic nettle extract incorporated into feed over a 60-day period, using inclusion levels of 50, 100, 200 and 400 mg/kg feed. At the end of the trial, the fish were subjected to an experimental challenge with Vibrio anguillarum, a bacterium associated with significant infectious outbreaks in farmed marine fish species.
The most notable result was obtained with the 100 mg/kg dose, which achieved a 96% survival rate following infection. By comparison, the control group recorded a survival rate of 33%, while the remaining nettle treatments also improved resistance to the pathogen, with survival rates of 70%, 62% and 76% depending on the dose used.
The researchers also observed activation of several innate immune parameters, including lysozyme and myeloperoxidase activity, together with changes in the expression of genes associated with inflammatory and immune responses. According to the authors, the 100 mg/kg dose showed the most consistent balance between immune stimulation and functional protection against infection.
The study also evaluated extract from Phillyrea latifolia, a Mediterranean shrub related to wild olive species, which showed preliminary immunomodulatory effects. However, in this case the results should be interpreted more cautiously, as they could not be validated through an effective bacterial challenge comparable to the one carried out with nettle extract.
The authors conclude that supplementation with nettle extract at 100 mg/kg feed was the most promising option under the tested conditions. The findings reinforce growing interest in plant-based functional additives as part of preventive strategies aimed at improving the health resilience of gilthead seabream and reducing dependence on corrective interventions against bacterial infections.
Reference: Evaluation of Urtica dioica and Phillyrea latifolia extracts as feed additives for enhancing innate immunity in gilthead seabream (Sparus aurata L.). Fish Physiology and Biochemistry, 2026.
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