Interactive effects of temperature and salinity on the growth and cytotoxicity of the fish-killing microalgal species Heterosigma akashiwo and Pseudochattonella verruculosa.

Fish-killing blooms of Heterosigma akashiwo and Pseudochattonella verruculosa have been devastating for the farmed salmon industry, but in Southern Chile the conditions that promote the growth and toxicity of these microalgae are poorly understood. This study examined the effects of different combinations of temperature (12, 15, 18 °C) and salinity (10, 20, 30 psu) on the growth of Chilean strains of these two species. The results showed that the optimal growth conditions for H. akashiwo and P. verruculosa differed, with a maximum rate of 0.99 day-1 obtained at 15 °C and a salinity of 20 psu for H. akashiwo, and a maximum rate of 1.06 day-1 obtained at 18 °C and a salinity of 30 psu for P. verruculosa. Cytotoxic assays (2 × 101 - 2 × 105 cell mL-1; cells, filtrates, and cell lysates) performed at salinities of 20 and 30 psu showed a 100% reduction in the viability of embryonic fish cells exposed to intact cells of H. akashiwo and a 39% reduction following exposure to culture filtrates of P. verruculosa. Differences in the fish-killing mechanisms (direct cell contact vs. extracellular substances) and physiological traits of H. akashiwo and P. verruculosa explain the recent occurrence of very large blooms under contrasting (cold-brackish vs. hot-salty) extreme climate conditions in Chile.

Fast detection of Piscirickettsia salmonis in Salmo salar serum through MALDI-TOF-MS profiling.

Piscirickettsia salmonis is a pathogenic bacteria known as the aetiological agent of the salmonid rickettsial syndrome and causes a high mortality in farmed salmonid fishes. Detection of P. salmonis in farmed fishes is based mainly on molecular biology and immunohistochemistry techniques. These techniques are in most of the cases expensive and time consuming. In the search of new alternatives to detect the presence of P. salmonis in salmonid fishes, this work proposed the use of MALDI-TOF-MS to compare serum protein profiles from Salmo salar fish, including experimentally infected and non-infected fishes using principal component analysis (PCA). Samples were obtained from a controlled bioassay where S. salar was challenged with P. salmonis in a cohabitation model and classified according to the presence or absence of the bacteria by real time PCR analysis. MALDI spectra of the fish serum samples showed differences in its serum protein composition. These differences were corroborated with PCA analysis. The results demonstrated that the use of both MALDI-TOF-MS and PCA represents a useful tool to discriminate the fish status through the analysis of salmonid serum samples.