Devastating farmed abalone mortalities attributed to yessotoxin-producing dinoflagellates.

A large dinoflagellate bloom in Walker Bay (South Africa) in January 2017 impacted 3 land-based abalone farms resulting in the death of several million animals. Satellite-derived images of Chl-a from the Ocean and Land Colour Imager (OLCI) on board the European Space Agency Sentinel-3 A showed bloom initiation in late December 2016 and dispersal in mid-February 2017. The bloom was dominated by two dinoflagellate species identified by light microscopy as Gonyaulax spinifera (Claparède & Lachmann) Diesing, 1866 and Lingulodinium polyedrum (Stein) Dodge, 1989. These morphologically based identifications were confirmed by phylogenetic analysis using partial sequences of the large subunit rDNA of both dinoflagellates. The appearance of yessotoxins (YTX) in abalone clearly coincided with increases in dinoflagellate concentrations. Yessotoxins in both the plankton and abalone were dominated by the two analogues homo-YTX and 45-hydroxy-YTX. The absence of toxins in a clonal culture of L. polyedrum implicated G. spinifera as the likely source of YTX. Toxin concentrations were found to be highest in the gills which showed the most significant pathology, including severe, generalized disruption of the gill epithelium characterized by degeneration and necrosis of epithelial cells accompanied by a modest inflammatory response. Some farms undertook pre-emptive or emergency harvesting to reduce financial losses.

Ichthyobodo necator (Kinetoplastida)--a complex of sibling species.

Ichthyobodo necator is a parasitic flagellate that attacks fishes, causing disease problems in freshwater worldwide. Findings of similar flagellates in strictly marine fishes have indicated that ichthyobodiosis may be caused by more than 1 flagellate species. We obtained partial small subunit rDNA (ssu rDNA) sequences of 14 Ichthyobodo isolates originating from fishes in Norway, Japan, Singapore, South Africa and Brazil, and identified 8 strains or species, including 2 species infecting cultured salmon in Norway. An Ichthyobodo species isolated from the skin of Atlantic salmon parr in freshwater is suggested to represent L. necator sensu stricto, while another species, showing particular affinity for the gills, infects salmon in both fresh- and seawater. Atlantic cod is infected with a marine Ichthyobodo species unrelated to those infecting salmonids; 2 cyprinids originating from different parts of the world had related Ichthyobodo strains/species, and 2 isolates from unrelated North and South American fishes were also closely related. The phylogenetic relationships of the Ichthyobodo isolates is described, and the implications of the molecular findings on past and future morphological studies of Ichthyobodo spp. are discussed.