Immune adaptive response induced by Bicotylophora trachinoti (Monogenea: Diclidophoridae) infestation in pompano Trachinotus marginatus (Perciformes: Carangidae)

Fish have developed protective strategies against monogeneans through immunological responses. In this study, immune adaptive response to parasites was analysed in the pompano Trachinotus marginatus infested by Bicotylophora trachinoti. Hosts were pre-treated with formalin and after 10 days assigned to one of the following experimental treatments: (1) fish infested with remaining eggs of B. trachinoti; (2) fish infested with remaining eggs of B. trachinoti and experimentally re-infested by exposure to T. marginatus heavily infested with B. trachinoti. Samples were collected at 0, 15, and 30 days. Gills were dissected to check the presence of B. trachinoti. Blood was collected for haematological and biochemical assays. Spleen and head-kidney were dissected for phagocytosis assay. The spleen-somatic index was also calculated. Re-infested fish showed a faster and higher parasite infestation than infested ones. The parasite mean abundance at 15 days was 24.86 ± 13.32 and 11.67 ± 8.57 for re-infested and infested fish, respectively. In both groups, hosts showed an immune adaptive response to parasite infestation that was marked by an increased number of leukocytes. Also, phagocytosis (%) in spleen and head-kidney cells was stimulated after parasite infestation (92.50 ± 3.73 and 66.00 ± 9.54, respectively), becoming later depressed (77.39 ± 6.69 and 53.23 ± 9.14, respectively). These results support the hypothesis that monogenean infestation induces a biphasic response of the non-specific defence mechanisms in the pompano T. marginatus. This response is marked by an initial stimulation followed by a later depression of the non-specific defence mechanisms.