Short-term immune responses of Gilthead Seabream (Sparus aurata) Juveniles against Photobacterium damselae subsp. piscicida

Funding: This research was supported by project BE4AQUAHEALTH: RASTREIO NACIONAL DE PATOLOGIAS DE PEIXES DE AQUACULTURA: UMA APOSTA NA PREVENÇÃO (16-02-05-FMP0013), funded by Mar2020 Operational Programme and the European Union through FEDER and by Fundação para a Ciência e Tecnologia (FCT), through the strategic project UID/MAR/04292/2020 granted to MARE. BC was supported by FCT, Portugal (IF/00197/2015).

Photobacteriosis is a septicaemic bacterial disease affecting several marine species around the globe, resulting in significant economic losses. Although many studies have been performed related to the pathogen virulence and resistance factors, information regarding the host defence mechanisms activated once an infection takes place is still scarce. The present study was designed to understand innate immune responses of farmed juvenile gilthead seabream (Sparus aurata) after Photobacterium damselae subsp. piscicida (Phdp) infection. Therefore, two groups of seabream juveniles were intraperitoneally injected with 100 uL of PBS (placebo) or 100 uL of exponentially growing Phdp (1 x 106 CFU/mL; infected). The blood, plasma, liver, and head kidney of six fish from each treatment were sampled immediately before infection and 3, 6, 9, 24 and 48 h after infection for the broad screening of fish immune and oxidative stress responses. Infected animals presented marked anaemia, neutrophilia and monocytosis, conditions that are correlated with an increased expression of genes related to inflammation and phagocytic activity. Similar studies with different fish species and bacteria can be useful for the definition of health biomarkers that might help fish farmers to prevent the occurrence of such diseases.

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