Immunoprophylactic potential of parasite-derived antigens for controlling Lernaea cyprinacea infection in Ctenopharyngodon idella.

Lernaea cyprinacea, an invasive ectoparasitic copepod, poses a significant threat to freshwater aquaculture due to its high pathogenicity and association with severe epizootics leading to mass fish mortalities. The present study evaluated the immunogenic potential of parasite-derived antigens in Ctenopharyngodon idella (grass carp) as a immunoprophylactic strategy against L. cyprinacea infection. Crude antigens isolated from L. cyprinacea were administered intraperitoneally to the experimental group, whereas the control group received phosphate-buffered saline (PBS), and a naturally infected group received no treatment. Immunological and physiological responses were assessed through hematological profiling, quantification of protein and assessment of non-specific immune parameters, including protease and lysozyme activities, at defined post-immunization intervals. After 28 days of immunization, fish were experimentally challenged with live L. cyprinacea to evaluate protective efficacy. Immunized fish demonstrated significant improvements in hematological indices, with serum protein concentrations comparable to uninfected controls but markedly higher than those of infected fish, reflecting enhanced immune competence. Lysozyme activity exhibited a consistent and significant elevation, surpassing both control groups and indicating potentiation of innate immune defenses. Similarly, enhanced protease activity at post-immunization suggested acute immune activation. Challenge trials confirmed a notable reduction in parasite load among immunized fish, underscoring the protective efficacy of antigen-based immunization. These findings highlight L. cyprinacea-derived antigens as a promising immunoprophylactic strategy for sustainable lernaeosis control in freshwater aquaculture.