In vitro hemocyte phagocytosis activation after experimental infection of common octopus, Octopus vulgaris (Cuvier, 1797) with Photobacterium damselae subsp. piscicida or Vibrio alginolyticus at different temperatures and infection routes

[Display omitted] •Experimental animals infected with Vibrio alginolyticus showed evidence of disease development and discomfort and the pathogen may be impacting negatively hemocyte mobilization or success.•Levels of circulating hemocytes showed great individual variability within the same season, being probably influenced by many intrinsic and extrinsic factors, and making interpretation of reactions a difficult task.•Pathogen species could be playing an important role and on phagocytosis ability.•Temperature apparently affects circulating hemocyte numbers as well as hemocyte phagocytosis activity.•Specimens infected with Photobacterium damselae subsp. piscicida showed more activated hemocytes at lower temperature and different levels of stimulation in any given route of infection. Due to the fast growth rate, the short life cycle, the high market price and the high food conversion efficiency, O. vulgaris is considered as a good candidate for aquaculture. One of the prerequisites for the successful integration of new species, such as octopi, into industrial-scale production, is the knowledge of the pathological conditions that may arise, with emphasis on infectious diseases caused by microorganisms and para-sites transmitted through wild populations, especially for the farmed organisms cul-tured in cages in proximity to teleost fish. The main objectives of this study were to investigate the sensitivity of common octopus to experimental infection with pathogenic bacteria, to assess the activation of hemocytes and more specifically their phagocytic activity after infection and to associate sensitivity of the species and phagocytic activity of hemocytes to temperature changes, route of infection and pathogen. Common octopus individuals were intramuscularly and intravenously infected with either Photobacterium damselae subsp. piscicida or Vibrio alginolyticus. The hemocyte phagocytosis activation in vitro at two temperatures (21 ± 0.5 °C and 24 ± 0.5 °C) was studied, in an effort to relate these aspects to climate change. Hemolymph was withdrawn on days 0, 3 and 7 post infections/injections. Number of circulating hemocytes/ml hemolymph, phagocytosis ability and Phagocytosis Particle Binding Intensity index were determined. Correlations between hemocytes and bodyweight and between hemocytes and phagocytosis ability were also determined. No mortalities were recorded irrespective of pathogen, route of infection and temperature employed. Circulating hemocytes in