Journal of Marine Biology

Protozoan Trichodina parasites that attach to the skin, gills, and fins of freshwater and marine fish cause tissue damage and secondary infections and, under intensive aquaculture conditions, are regarded as a serious threat to fish health and farm productivity due to their direct life cycle and rapid transmission. Environmental stressors such as poor water quality, temperature fluctuations, and increased organic loads that suppress the fish immune system promote the rapid proliferation and spread of these parasites. Clinical signs include excessive mucus secretion from the skin and gills, respiratory distress, inflammation and cutaneous lesions, reduced appetite, and abnormal behavior; in severe cases, these may lead to sudden mortality, particularly in fry and juveniles. Accurate diagnosis of Trichodina relies on sampling and microscopic examination to identify the parasite’s characteristic morphology, silver nitrate staining, and, more recently, molecular approaches (PCR) and gene sequencing. Treatment of trichodiniasis commonly involves a combination of chemical methods, including formaldehyde (formalin), sodium chloride, and acriflavine, which improve fish health by disrupting parasite cellular structures, reducing parasite burden, and preventing replication. Peracetic acid is also effective in reducing parasite loads and controlling pathogenic bacteria such as Aeromonas hydrophila. In addition, medicinal plants and probiotic supplementation, as biological and immunostimulatory strategies, together with optimized husbandry practices reducing stocking density and maintaining water quality are of particular importance. Overall, effective control of Trichodina in aquaculture requires a thorough understanding of parasite biology, an integrated application of chemical and biological interventions, and appropriate environmental management to minimize economic losses and ensure fish health and sustainable production.