Experimental infection of octopus vulgaris (Cuvier, 1797) with Photobacterium damsela subsp. piscicida. Immunohistochemical tracking of antigen and tissue responses

The effect of temperature and challenge route on in vitro hemocyte phagocytosis activation after experimental challenge of common octopus, Octopus vulgaris (Cuvier, 1797) with either Photobacterium damselae subsp. damselae or Vibrio anguillarum O1

Infectious diseases in aquaculture could be associated with high mortalities and morbidity rates, resulting in negative impacts to fish farming industry, consumers, and the environment. Octopods are reared near marine fish farming areas, and this may represent a major risk since fish pathogens may cause pathologies to octopods. Up to date cephalopods immune defense and pathologies, are incompletely understood. Therefore, the aim of this study was to determine the effect of water temperature and challenge route on hemocyte phagocytosis in vitro after experimental challenge of common octopus with Photobacterium damselae subsp. damselae or Vibrio anguillarum O1. Hemolymph was withdrawn at various time-points post-challenge and the number of circulating hemocytes, and phagocytosis ability were determined. No mortalities were recorded irrespective of pathogen, route of challenge and temperature employed. Great variation was observed in the number of circulating hemocytes of both control and challenged specimens in both experiments (1.04 × 10⁵ to 22.33 × 10⁵ hemocytes/ml for the Photobacterium damselae subsp. damselae challenge and 1.35 × 10⁵ to 24.63 × 10⁵ hemocytes/ml for the Vibrio anguillarum O1 and at both studied temperatures). No correlation was found between circulating hemocytes and baseline control specimens body weight. Probably, the number of circulating hemocytes is affected by many extrinsic, and intrinsic factors such as size, age, maturity stage, natural fluctuations and temperature, as indicated in the literature. The hemocyte foreign particles binding ability observed in Photobacterium damselae subsp. damselae experiments, at 21 ± 0.5 °C and 24 ± 0.5 °C, was (mean ± SD) 2.26 ± 2.96 and 11.72 ± 12.36 yeast cells/hemocyte for baseline specimens and 7.84 ± 8.88 and 8.56 ± 9.89 yeast cells/hemocyte for control and challenged specimens, respectively. The corresponding values for Vibrio anguillarum O1 experiments were (mean ± SD) 6.68 ± 9.26 and 7.00 ± 8.11 yeast cells/hemocyte for baseline specimens and 8.82 ± 9.75 and 6.04 ± 7.64 yeast cells/hemocyte for control and challenged specimens, respectively. Hemocytes of the Photobacterium damselae subsp. damselae and Vibrio anguillarum O1 challenged specimens, were more activated at lower temperature. Apparently, temperature is an important factor in hemocyte activation. In addition, our results indicated that time post challenge, route of challenge and pathogen may influence phagocytosis ability.