Vibrio parahaemolyticus, Perkinsus sp. AND PHYCOTOXINS: AN ASSESSMENT OF THE HEALTH STATUS OF OYSTERS CULTURED IN PARANAGUA BAY, BRAZIL

While feeding, oysters can retain in their tissues pathogenic microorganisms and toxins produced by microalgae, being a potential source of damages to the aquaculture and to the public health. This study conducted between 2016 and 2017 evaluated sanitary aspects of Crassostrea sp. in two farms, PO and MED, located in the Estuarine Complex of Paranaguá (CEP), Paraná-Brazil. Fermentation in multiple tubes indicated the occurrence of Vibrio parahaemolyticus; culture in Ray Fluid Thioglycollate Medium (RFTM), histopathology and Polymerase Chain Reaction (PCR) determined the prevalence of Perkinsus sp.; count in inverted microscope for quantification of potentially toxic microalgae; and liquid chromatography (LC-MS/MS and HPLC) detected phycotoxins in oyster tissues and the particulate fraction of seawater. Biological variables were related to dominant abiotic factors and to each other to evaluate the existence of significant interactions in the environment

Water temperature was higher in april/17 (26.5±0.6°C) and lower in october/16 (21.3±0.5°C). Salinity values ​​differed between MED (20 to 22) and PO (24 to 36). Conversely, the concentrations of phosphate, silicate and ammonium did not differ between sites over time. This study made the first report of the presence of Perkinsus marinus and P. cf. olseni in oysters Crassostrea sp. from the CEP. The intensity of the infection was predominantly low, except in june/17, considered intense. The prevalence ranged from 30 to 75% by RFTM and 10 to 75% by PCR, is consistently higher in november/16 in oysters from PO.

Vibrio parahaemolyticus was found in oysters from both MED and PO, with the highest densities (> 1.100 NMP.g^-1) recorded in november/16 and april/17. In water, the densities of V. parahaemolyticus were higher in april/17 (> 1.100 NMP.mL^-1). In the plankton, diatoms were more abundant than dinoflagellates throughout the study period, with total microalgae abundance higher in april/17.

Potentially toxic microalgae occurred in both sites: the dinoflagellate Dinophysis cf. acuminata (617 cel.L^-1 in MED and 121,265 cel.L^-1 in the PO) and the diatoms Pseudo-nitzschia calliantha (252,989±163,600 cel.L^-1) and Pseudo-nitzschia punges (6,779±11,732 cel.L^-1) in april/17. Low concentrations of ocadaic acid in plankton were detected in june/17 in MED (0.24-4.10 μg.L^-1) and PO (1.57-1.83 μg.L^-1) , and high concentrations in the digestive glands of the bivalves, in june/16 in the PO (639±287 μg.L^-1). However, the domoic acid was not detected in either plankton or oysters.

The results suggest that phytoplankton may favor the microbiological growth and dispersion of pathogens in the medium also provide a higher concentration of this pathogen in soft tissues of oysters, since phytoplankton is its main food component. Consequently, they may affect the susceptibility of bivalves to pathogens, such as the Perkinsus genus. The densities of V. parahaemolyticus, D. cf. acuminata, Pseudo-nitzschia spp. and Perkinsus spp. found in this work generate concern about the maintenance of the cultivation activity also the potential damages to human health.