Pseudochattonella cf. verruculosa is a phytoflagellate, Dictyochophyceae class that has abundant golden chloroplasts. It has two flagella, one of which, is directed forward, thereby allowing cell movement.
The cell size varies between 12 – 45 microns depending on the stage of its life cycle. Its surface, the cell is covered by specialized structures that resemble papillae or warts, hence the name “verrucous”. These structures are mucocysts through which mucus is discharged.
It is distributed in water bodies that fluctuate between 10 – 18 oC, salinities between 11-32 ppm and relatively high nitrate concentrations.
It has been reported in Germany, Denmark, Sweden, Norway, Japan and southern Chile. At the beginning of 2016, high and persistent densities of Pseudochattonella cf. verruculosa and A. catenella were detected in the estuarine and marine ecosystems of southern Chile.
The mechanism of toxicity is still unknown, but the most common effects include acute gill irritation and damage, reducing gas exchange efficiency. Osmotic stress can be considered as a determining factor because it would generate the lysis of the cell that accelerates the mortality of salmon.
The toxicity threshold for Pseudochattonella cf. verruculose, is <1 cell / mL, but at 11° C, this threshold increases significantly until reaching the value of 2150 cells / mL.
Affected fish show high mortalities, superficial swimming, lethargy, and they have branchial petechiae. Histopathology shows lamellar aneurysms and diffuse lamellar thrombosis, lamellar epithelial necrosis and branchial hyperplasia. Multifocal hepatic necrosis is also observed, no doubt due to hypoxaemia.
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