Host-parasite relationship Octopus tehuelchus - Aggregata valdessensis in Patagonian coast, southwestern Atlantic Ocean

Abstract

Histological lesions associated with the apicomplexan Aggregata valdessensis on wild population of Octopus tehuelchus was studied. Moreover, the digestive gland index, total hemocyte counts, and growth parameter (RNA/DNA ratio) were analyzed to assess the effect of the disease. To establish which factors (seawater temperature, size, sex and maturity gonad stages of octopuses) explain the prevalence and the infection intensity of parasites, Generalized Linear Models (GLMs) were applied. Lesions including loss of intestinal epithelium and destruction of the tissue organ architecture as well as the replacement of host tissue by parasites were associated with infection. The infection caused an inflammatory defensive response in form of hemocytic infiltration and encapsulation. Prevalence of apicomplexan increased with octopus size (GLM, t = 2.68; p = 0.007). Infection intensity was significant higher in males octopus (GLM, t = 2.69; p = 0.009) and decreased at higher temperatures (GLM, t = -2.42; p = 0.018). The digestive gland condition index did not significantly vary with infection intensity, and no significant relationship between total hemocyte counts and coccidian infection was found (Lineal Model, t = 0.46; p = 0.64). The acid nucleic ratio was significantly lower in octopuses infected by A. valdessensis (Kruskal Wallis test, H = 4.8; p = 0.02), suggesting a detrimental effect on O. tehuelchus growth caused by the coccidian.