Bee glue for fish farms: propolis shows promise as a natural immunostimulant and antimicrobial

Propolis, the resinous bee glue that honeybees use to seal and defend their hives, is emerging as one of the most versatile natural candidates for replacing synthetic chemicals in fish farming. A review published in Aquaculture Science and Management on 26 February 2026 pulls together decades of research on this sticky substance, which bees manufacture from plant buds, exudates and pollen blended with salivary enzymes such as beta-glucosidase that hydrolyse flavonoid glycosides into their active aglycone forms. The review, led by Mutum Sardalini and colleagues, argues that propolis deserves a central place in the search for sustainable aquaculture additives, while also flagging the knowledge gaps that still stand between laboratory promise and commercial practice.

The timing is significant. According to the Food and Agriculture Organization’s 2024 figures cited in the review, global fisheries and aquaculture output reached 223.2 million tonnes in 2022, with aquaculture contributing 51 percent and exceeding capture fisheries for the first time. That milestone underscores how rapidly the sector is growing, but intensification has come at a cost. Chemical treatments are routinely deployed to control disease, improve larval survival, enhance feed efficiency, reduce transport stress and maintain water quality, and their continued use raises concerns about toxic effects on farmed species, surrounding ecosystems and human health. This has fuelled interest in natural alternatives, and propolis has drawn particular scientific attention for its antiseptic, antimicrobial, antioxidant, anti-inflammatory and bacteriostatic properties.

Chemically, propolis is a complex matrix containing more than 200 bioactive compounds, including flavonoids such as flavones, flavanones, flavonols, chalcones and dihydroflavonols, phenolic acids and esters, terpenes, steroids, aromatic alcohols and aldehydes, sesquiterpenes and stilbene derivatives. On average, raw propolis consists of roughly 50 percent resins and balsams, 30 percent beeswax, 10 percent essential oils, 5 percent pollen and trace levels of other elements. Its composition varies with botanical and geographical origin: poplar-type propolis dominates in Europe, North America and non-tropical Asia, Brazilian green propolis derives from Baccharis dracunculifolia, red propolis from Clusia species originates in Cuba and Venezuela, and birch and Mediterranean conifer types have also been described. This variability is not trivial. The review stresses that biological efficacy is intrinsically linked to chemical profile, and it calls for quantification of key constituents such as caffeic acid phenethyl ester, artepillin C and other phenolic markers, along with HPLC fingerprinting, to enable meaningful cross-study comparisons.

The growth-promoting evidence is strikingly species-dependent. In Nile tilapia, supplementation with ethanolic extract of propolis at 10 grams per kilogram enhanced specific growth rate, feed conversion ratio and feed efficiency, while crude propolis at 1.83 to 2.74 grams per kilogram increased weight gain. Water extract at 25 grams per kilogram improved body length and feed metrics. In rainbow trout, ethanolic extract at 2 to 4 grams per kilogram improved weight gain, specific growth rate, feed efficiency and protein efficiency ratio, and higher inclusion levels of 10 to 30 grams per kilogram further enhanced growth, though lower doses of 0.5 to 2 grams per kilogram did not yield significant benefits. In other species, crude propolis at 2.5 to 5 grams per kilogram improved growth in Japanese seabream, water extract at 2.5 grams per kilogram enhanced specific growth rate in European seabass, and extract at 2 to 10 grams per kilogram improved growth rate in Pangasius djambal. Yet in common carp, ethanolic extract at 1 to 4 grams per kilogram produced no significant growth improvements, a reminder that propolis is not a universal growth promoter.

The immunostimulatory picture is more consistent, though still shaped by species, dose and delivery route. In gilthead seabream, intraperitoneal injection of water and ethanolic extracts at 5 milligrams per millilitre failed to elicit measurable immune improvements, but the same extract incorporated into the diet at 10 grams per kilogram produced notable immunostimulatory effects, suggesting oral delivery may be more effective for that species. In gibel carp, injection of water extract at 50 milligrams per millilitre significantly stimulated leukocyte activity, and in turbot, injection of ethanolic extract at 15 milligrams per millilitre enhanced lysozyme activity and superoxide dismutase. In Nile tilapia, crude or ethanolic extracts at 10 grams per kilogram improved lysozyme activity, hematocrit values and lymphocyte counts, and further work showed increased thrombocyte levels at doses of 5, 10 and 20 grams per kilogram. In rainbow trout, bath treatments with ethanolic extract at 20 to 30 milligrams per litre elevated leukocyte counts and antioxidant responses, while dietary supplementation at 1 to 4 grams per kilogram increased total antioxidant capacity, lysozyme activity and superoxide dismutase.

Freshwater species have provided particularly strong evidence of mucosal and cellular immune benefits. In Wuchang bream, dietary crude propolis combined with Herba epimedii in a 3:1 ratio significantly enhanced plasma lysozyme activity and phagocytic capacity, indicating synergistic effects with herbal immunostimulants. In Japanese eel, dietary crude propolis at 2.5 to 5 grams per kilogram enhanced lysozyme activity in both serum and mucus, reinforcing mucosal immunity. In European seabass, water extract at 2.5 grams per kilogram reduced plasma cortisol and glucose levels, suggesting propolis also alleviates stress. In channel catfish, injection of ethanolic extract combined with truncated C5a peptidase improved survival rates, enhanced antibody production and increased lysozyme activity, pointing to potential as a vaccine adjuvant. Beyond immunity, the review documents protective effects against chemical stressors including metrifonate, malathion, arsenic, glyphosate, chromium, chlorpyrifos and oxytetracycline, and in tilapia exposed to malathion toxicity, bee pollen with propolis decreased chromosomal abnormalities, DNA fragmentation and micronuclei formation.

Antimicrobial and antiparasitic activity rounds out the therapeutic profile. Propolis antibacterial effects are attributed to flavonoids, phenolic acids and their esters, phenolic aldehydes and ketones, with compounds such as quercetin, naringenin, caffeic acid and caffeic acid phenethyl ester disrupting cytoplasmic membrane integrity, dissipating membrane potential, inhibiting bacterial motility and suppressing enzyme activity. A notable antiparasitic trial by de la Cruz-Cervantes and colleagues evaluated an ethanol extract of propolis against the monogenean Ligictaluridus floridanus in channel catfish. In vitro assays at 5, 30 and 60 milligrams per litre showed a clear dose-dependent response, with 60 milligrams per litre significantly reducing parasite survival time. In a complementary in vivo trial involving 72 naturally infected fish given one-hour propolis baths every 72 hours over 16 weeks, repeated exposure to 60 milligrams per litre markedly decreased parasite intensity and abundance on the gills, with no mortality or adverse effects observed. The review identifies this as the first documented challenge test confirming anthelmintic potential of propolis against this parasite in catfish.

Reproductive performance adds another dimension. Feeding Nile tilapia water-extract propolis at 25 grams per kilogram for 21 days greatly increased semen quality and overall fertility, and propolis added to fish diets at 0.8 to 1 milligram per kilogram has been shown to protect sperm cells against cryo-induced damage, with preserved DNA integrity during freezing and thawing attributed to antioxidant scavenging of excess reactive oxygen species. Ogretmen and colleagues reported notable enhancements in sperm motility, viability and post-thaw hatching success in common carp, confirming protective effects during sperm storage. These findings position propolis as a promising natural additive for enhancing reproductive outcomes, both under normal conditions and during bioprotective sperm preservation.

Safety considerations temper the enthusiasm. Propolis and several of its constituents, most notably caffeic acid esters such as 3-methyl-2-butenyl caffeate, benzyl caffeate, phenethyl caffeate and geranyl caffeate, are strong sensitizers. In guinea pig maximising tests, 19 out of 25 animals became sensitised, and occupational contact allergy in beekeepers has been documented since the first reported case in 1915. However, the review notes there is currently no evidence of allergen transfer from propolis-fed fish to human consumers, and food safety studies to date show propolis residues in foods to be low and not associated with toxicological concern. Critically, no studies have specifically quantified propolis residues in fish muscle, and preservation-focused investigations, including xanthan gum coatings enriched with propolis extract at 1 to 2 percent that extended the shelf life of refrigerated mackerel fillets for up to 20 days while suppressing microbial growth, did not quantify transfer or accumulation of propolis-derived compounds in edible tissue. Similarly, no occupational allergy cases have been documented among aquaculture workers handling propolis-supplemented feeds or fillets, though sensitization patterns in beekeepers and cosmetic-industry workers suggest repeated dermal or aerosol exposure could present a risk.

The review’s synthesis distils several consistent themes. Dose-dependency is a key determinant of efficacy, with 0.5 percent ethanolic extract consistently eliciting the strongest immune responses in common carp, where immune metrics improve but growth does not. Nile tilapia and rainbow trout exhibit both growth and immune enhancement, while Japanese eel require higher propolis levels for immune activation, with 0.25 to 0.5 percent supporting optimal growth and 0.5 to 1 percent needed for enhanced immune function and disease resistance. Ethanolic extracts outperform aqueous extracts and crude propolis across species due to higher solubility of phenolics and flavonoids, and dietary application has proven the most consistent delivery method, while injection and bath treatments may enhance immunity in select species but have limited large-scale practicality. The authors conclude that current evidence supports propolis as a versatile natural additive capable of improving immunity, mitigating oxidative stress, enhancing reproductive performance and reducing dependence on synthetic chemicals, but they emphasise that standardized extraction protocols, detailed chemical profiling, long-term safety and toxicity assessments, allergenicity and residue transfer evaluation, and field-scale validation trials remain essential before propolis can be deployed with confidence across commercial production systems.

Subject of Research: Propolis as a natural immunostimulant and antimicrobial feed additive in aquaculture

Article Title: From hive to pond: exploring propolis as a natural immunostimulant and antimicrobial in aquaculture

Article References: Sardalini, M., Iqbal, G., Rashid, F., Kent, B., Asimi, O., & Saba, K. (2026). From hive to pond: exploring propolis as a natural immunostimulant and antimicrobial in aquaculture. Aquaculture Science and Management, 3(1), Article 3. https://doi.org/10.1186/s44365-026-00032-y

Image Credits: AI Generated

DOI: 10.1186/s44365-026-00032-y

Keywords: propolis, aquaculture, immunostimulant, antimicrobial, fish health, Nile tilapia, rainbow trout, common carp, Japanese eel, feed additive, natural alternatives, bee products