Tilapia aquaculture faces constant health challenges. Among them, vibriosis, caused by bacteria of the genus Vibrio, such as Vibrio alginolyticus, generates significant economic losses. A recent study explores the potential of the “undulated surf clam” Paratapes undulata as a natural and sustainable biocontrol agent, offering a ray of hope for managing this disease in red tilapia (Oreochromis sp.) fish farming.
Researchers from the Animal Health Research Institute (AHRI) and Zagazig University published their study in the journal Scientific Reports, where they demonstrate the therapeutic potential of the undulated surf clam to mitigate Vibrio alginolyticus infection in red tilapia.
The growing problem of vibriosis and antibiotic resistance
Vibriosis not only affects the growth and survival of red tilapia, a commercially important species, but also increases the dependence on antibiotics in aquaculture. This dependence carries the risk of developing resistant bacterial strains, a public health and environmental problem of growing concern.
The study highlights that V. alginolyticus is particularly problematic in open culture systems, where red tilapia is more vulnerable. In fact, isolates of V. alginolyticus were identified with a high prevalence of virulence genes and a concerning profile of multidrug resistance, including extensively drug-resistant (XDR) phenotypes.
Paratapes undulata: a new ally from the sea
Given this scenario, scientific research has focused on finding sustainable alternatives. The study in question focused on Paratapes undulata, a locally abundant bivalve clam, selected for its unique profile of bioactive compounds such as terpenoids, alkaloids, and polyphenols. These compounds suggest a robust natural defense mechanism that could be harnessed in aquaculture. Unlike other natural antimicrobial agents, P. undulata stands out for its potential broad-spectrum activity, high compound stability, and ease of access.
How was the clam’s effect investigated?
The researchers conducted an in vivo study to evaluate the efficacy of P. undulata. Red tilapias were divided into four experimental groups:
- G1 (Negative Control): Healthy fish without treatment or infection.
- G2 (Infected Control): Fish infected with V. alginolyticus without clam treatment.
- G3 (Clam-treated Control): Healthy fish exposed to water from tanks with P. undulata.
- G4 (Clam-treated Infected): Fish infected with V. alginolyticus and exposed to water from tanks with P. undulata.
For 16 days (including 7 days for acclimation and infection istered on the 9th day), researchers monitored key parameters such as growth performance, mortality rates, and clinical signs, and hematological, biochemical, histopathological, and gene expression analyses were performed. Additionally, a methanolic extract of P. undulata was prepared to evaluate its antimicrobial activity in vitro.
Surprising results: healthier and more productive tilapia
The study’s findings are notably positive and open a new avenue for health management in tilapia aquaculture.
Significant growth improvement
The tilapia groups that were in with P. undulata (G3 and G4) showed significantly greater growth. Compared to the untreated infected group (G2), growth in the G3 group (treated control) was approximately 362% higher, and in the G4 group (treated infected) 284% higher. Higher final weight, weight gain, and a better feed conversion ratio (FCR) were observed in the clam-treated groups, even in the presence of infection.
Drastic reduction in mortality
Exposure to P. undulata dramatically reduced mortality. Group G3 recorded no mortalities, while group G4 (infected and treated) had a 75% reduction in mortality compared to group G2 (infected untreated). In group G2, mortality peaked on the third day post-infection, whereas no deaths occurred in groups G1 and G3.
Alleviation of clinical signs and tissue damage
Fish treated with the clam showed a notable decrease in clinical signs associated with vibriosis and a significant reduction in tissue damage in organs such as gills, liver, spleen, and intestine. Histopathological examination revealed a marked improvement in organ integrity in the treated groups.
Strengthening of the immune system and reduction of oxidative stress
P. undulata positively modulated the tilapia’s immune response. Researchers observed a balance in cytokines, leaning towards an anti-inflammatory response (increase in IL-10 and IL-18 and decrease in pro-inflammatory ones like IL-1β and IL-6). Furthermore, the antioxidant capacity of the fish was enhanced, with an increase in the expression of genes like SOD and CAT. Levels of liver enzymes (ALT, AST, LDH), which rise due to cellular damage, were significantly lower in the treated fish, indicating liver protection.
Direct action against Vibrio alginolyticus
The study demonstrated that P. undulata not only strengthens the fish but also directly combats the pathogen. According to its results, an inhibition of V. alginolyticus virulence was observed, with a reduction in the expression of key pathogenicity genes (tdh, trh, and toxR). The methanolic extract of the clam showed potent in vitro antimicrobial activity, with a 30 mm inhibition zone and a minimum inhibitory concentration (MIC) of 4 µg/mL against a pan-drug resistant strain of V. alginolyticus.
What makes Paratapes undulata so special? The bioactive compounds
Through Gas Chromatography-Mass Spectrometry (GC-MS) and Fourier-Transform Infrared Spectroscopy (FTIR) analyses, a rich diversity of bioactive compounds was identified in the P. undulata extract. Among them, phenols, fatty acids and their esters, amides, and sterols stand out. Compounds such as desmosterol (a cholesterol precursor with potential anti-inflammatory properties), stigmasterol (a plant sterol exhibiting anti-inflammatory, antioxidant, and anti-cancer activities), and ergosterol (a vitamin D precursor with potential anti-microbial properties) were particularly noteworthy. These compounds, likely acting synergistically, would be responsible for the observed beneficial effects.
Implications for more sustainable and healthier tilapia aquaculture
The results of this study are highly promising and establish Paratapes undulata as a natural and effective biocontrol agent for vibriosis in red tilapia aquaculture. Its use could contribute to:
- Reducing dependence on antibiotics: Offering a natural alternative for managing bacterial diseases.
- Improving fish health and welfare: By strengthening the immune system and reducing stress.
- Increasing productivity: By improving growth and decreasing mortality.
- Promoting environmental sustainability: By using a natural resource and reducing the environmental impact associated with chemicals.
The researchers suggest that P. undulata could be incorporated into fish feed or water treatments, facilitating its practical application in fish farms.
Conclusion
This pioneering study conclusively demonstrates the therapeutic potential of Paratapes undulata to mitigate Vibrio alginolyticus infection in red tilapia. The reduction in mortality, improvement in fish health parameters, and effective modulation of the immune response highlight its multifaceted protective capabilities. The identification of its bioactive compounds opens the door for the development of optimized formulations.
While more research is needed to refine extraction processes, study the synergistic effects of the compounds, and conduct commercial-scale validations, clams are emerging as an innovative and sustainable strategy for disease control in aquaculture, contributing to safer food production and the health of aquatic ecosystems.
Azza SalahEldin El-Demerdash
Laboratory of Biotechnology, Department of Microbiology, Agricultural Research Center (ARC), Animal Health Research Institute (AHRI)
Zagazig, 44516, Egypt
Email: [email protected]
Reference (open access)
Mowafy, R.E., Megahed, H.M., Khadra, S.H.A. et al. Innovative vibriosis control in open aquaculture: Paratapes undulata as a sustainable growth and resistance enhancer in red tilapia. Sci Rep 15, 17750 (2025). https://doi.org/10.1038/s41598-025-01026-x
Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.
