Secretory/Excretory Protein (SEP) profiling of Lepeophtheirus salmonis (Gulen strain) copepodites induced by Dopamine: A comparative analysis between natural and artificial sea water

Background Lepeophtheirus salmonis ( L. salmonis ) is a crustacean ectoparasite that significantly impacts the salmon aquaculture industry. The copepodite stage is critical for successful host infestation, as failure to attach to the host results in the parasite's death. Once attached, copepodites must evade the host immune system to establish infestation and grow. Secretory/Excretory Proteins (SEPs) released by copepodites are hypothesized to play a role in immune evasion, supported by the mild inflammatory response observed in certain salmon species, particularly Atlantic salmon. Methods SEPs were collected from 1000 copepodites (n = 3) incubated in filtered artificial seawater (ASW) and filtered natural seawater (NSW), both with and without dopamine stimulation. After incubation, copepodites were removed, and SEP samples were buffer-exchanged, trypsin-digested, and analyzed using LC-MS/MS for protein identification and quantified. Identified proteins were classified into various functional categories. Results A higher number of protein classes were identified in SEPs from the artificial seawater group with dopamine stimulation (ADC) compared to the natural seawater group (NDC). Specifically, 1039 proteins were identified in the ADC group, while 263 proteins were identified in the artificial seawater group without dopamine stimulation (AC). Identified proteins included proteases (metalloproteases, serine proteases, cysteine proteases, aspartic proteases), protease inhibitors, peroxidases, oxidoreductases, vitellogenins, calcium-binding proteins, ferritin, NK-lysin, metabolite interconversion enzymes, cytoskeletal proteins, and heat-shock proteins. Conclusions This study highlights the diversity of SEPs released by L. salmonis copepodites. However, further characterization of these proteins is necessary to identify their specific roles in host immune evasion and infestation success and might inform strategies to mitigate its impact on aquaculture.