Introduction: In recent years, medicinal leeches have garnered considerable interest in medical therapies, disease treatment, and the cosmetic industry due to their unique biological properties. Among these features, the ability to secrete and deliver therapeutic enzymes into the host during blood feeding has positioned leeches as valuable organisms in biomedical applications (Petrauskiene et al., 2011; Montinari and Minelli, 2022). With the increasing global demand, natural populations of leeches have declined significantly, leading to the development and expansion of leech farming as a sustainable alternative (Firouzbakhsh and Sudagar, 2025). Despite its potential, leech aquaculture faces several challenges. Leeches are highly sensitive to environmental conditions, microbial infections, and physiological disorders. Common complications such as blood regurgitation and body deformities are frequently observed under suboptimal conditions. These issues not only reduce the overall productivity and market value of the leeches but also pose a risk of spreading pathogens to healthy populations (Grafskaia et al., 2019; Kwak et al., 2021; Firouzbakhsh et al., 2025). Regurgitation of ingested blood can lead to water contamination, oxygen depletion, and increased mortality within culture systems. Given these concerns, effective disease management and health-promoting strategies are crucial for the success of leech farming. The present study investigates the therapeutic potential of lincomycin, a lincosamide antibiotic, in reducing mortality and preventing body deformities and blood regurgitation in the Eastern medicinal leech (Hirudo orientalis). The findings of this research may contribute to the development of improved health management protocols in leech aquaculture systems.

Materials and Methods: In this study, a total of 90 specimens of the Eastern medicinal leech (Hirudo orientalis) were assigned to three treatment groups: matchstick leeches (Treatment 1), cosmetic leeches (Treatment 2), and medical-grade leeches (Treatment 3). Each treatment included three replicates, with 10 leeches placed in separate plastic containers per replicate. The leeches were maintained under controlled conditions at a temperature of 23 ± 1°C (Aminov et al., 2021). Approximately three liters of bovine blood were procured from certified sources for feeding purposes. To prevent coagulation during transportation and before feeding, heparin was added as an anticoagulant at a dose of 1650 IU per liter of blood, using one-gram vials of pharmaceutical-grade heparin (Manav et al., 2019; Firouzbakhsh et al., 2025). Each container was filled with three liters of dechlorinated water, to which the lincomycin antibiotic was added at a concentration of 2 mg/L. The water in each container was completely replaced every 24 hours, and the same concentration of lincomycin was re-administered after each water change (Bidmal et al., 2021; Firouzbakhsh et al., 2025).

Results and Discussion: Following the feeding of Hirudo orientalis leeches with fresh blood, daily examinations revealed the appearance of various body deformities in a subset of individuals. These abnormalities presented as irregular body shapes, including sausage-like, beaded, hourglass, and amphora forms. Additionally, regurgitation of blood post-feeding was observed in some cases, though this symptom was notably less frequent in matchstick-type and cosmetic leeches compared to medicinal ones. This may suggest a higher physiological sensitivity in larger leeches, possibly related to size, age, or metabolic rate. These symptoms are believed to result from a combination of factors, including post-feeding stress, microbial contamination—either from the blood source or the surrounding aquatic environment—and imbalances in environmental conditions such as temperature or oxygen levels. Such disturbances can significantly disrupt the leech’s physiological stability and may threaten their survival if left untreated (Wang et al., 2022). To manage these complications, treatment with the antibiotic lincomycin was initiated at a concentration of 2 mg/L for seven consecutive days. During this period, the water in the holding tanks (pet systems) was completely replaced every 24 hours, and the antibiotic was re-administered at the same dose after each water change. Environmental conditions, including a stable water temperature of 22–24°C, indirect lighting, and continuous aeration, were carefully maintained throughout the treatment period. Signs of recovery became apparent toward the end of the second week. These improvements included the gradual disappearance of body deformities, cessation of blood regurgitation, a noticeable reduction in visible microbial contamination in the water, and increased motility and responsiveness in the leeches. Final evaluation four weeks after the start of treatment showed recovery rates of 90% in matchstick-type leeches, 80% in cosmetic leeches, and 60% in medicinal leeches. The reduced response in medicinal leeches may be attributed to their larger body mass or differing physiological demands. Statistical analysis confirmed that lincomycin significantly reduced the occurrence of post-feeding deformities and regurgitation symptoms. In a related study, ceftriaxone was used as a prophylactic measure at a dose of 1 g/L immediately after feeding. After two weeks, both body deformities and mortality rates were significantly reduced. Recovery rates ranged between 70% and 90%, and no regurgitation was observed in treated leeches (Firouzbakhsh et al., 2025).

Conclusion: Emphasizing adherence to health protocols, improving water quality management, and implementing treatment procedures can help improve the health and survival of leeches. The ultimate goal is to utilize leeches as sustainable resources in the aquaculture, medical, and pharmaceutical industries through the use of modern and scientific methods.Information on blood clotting and how to treat it is very limited, making it difficult to access the literature. Therefore, the use of lincomycin can help breeders reduce the rate of blood clotting and vomiting in leeches.