Immune parameters in the common octopus (Octopus vulgaris Cuvier, 1797) naturally infected by the gastrointestinal protozoan parasite Aggregata octopiana

Health of wild and reared Octopus vulgaris is threatened by the most dangerous parasite for the octopus, the protozoan coccidia Aggregata octopiana. This host-parasite relationship was studied to analyze the effect of A. octopiana on the cellular immune parameters of O. vulgaris. A. octopiana sporocysts infecting the digestive tract of octopuses were counted in order to confirm two octopus groups of infection: 1) healthy (low parasite load, without histological caecum damage) and 2) sick (high parasite load and strong histological caecum damage). Cellular defense parameters (phagocytosis, respiratory burst (ROS) and nitric oxide (NO) production) were measured in the octopus hemolymph. In addition, i) infection degree (total parasitic infection or distributed by groups of infection (sick/healthy)), ii) octopus origin (wild or reared in floating cages), biometric data (sex, length, weight, maturity) and iii) season of collection were tested to know their contribution to the octopus cellular response. Results showed that season of collection and total parasitic infection were the most important factors affecting the phagocytic ability of hemocytes. Phagocytosis increased accordingly to the infection intensity and was particularly higher in Autumn (P < .01) relative to Winter and Spring. ROS (P < .01) and NO (P < .1) production decreased with the A. octopiana infection increase. Related to biometric data, a markedly decrease in NO was observed in heaviest octopuses (P < .01). Comparing wild and reared octopuses, the cytotoxic activity notably decreased in the former group. The present results evidenced for the first time that the intensity of infection by A. octopiana severely weaken the octopus cellular immune response. Statement of relevance: To date, the octopus rearing is still dependent of wild specimens for fattening. Wild octopuses harbor the coccidia Aggregata octopiana, which is proved to affect the octopus wellbeing at tissue and molecular level. The present study provides functional data that complement previous studies and show that coccidiosis modify the octopus cellular immune defense.