Ichthyobodo spp. – a large complex of sibling species
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PhD Candidate: Trond Einar Isaksen
Supervisor: Are Nylund
Financial support: Research Council of Norway
Flagellates belonging to the genus Ichthyobodo Pinto, 1928 are obligate ectoparasites that mainly infect fish. Massive infections (ichthyobodosis) cause destruction of the epithelial or epidermal cells and may result in severe osmoregulatory or respiratory problem to the host. In addition, epidermal damage to the skin makes the host more susceptible to secondary infections (e.g. bacteria, fungi), and proliferative gill diseases have been associated with Ichthyobodo infections on gills of salmonids in seawater. Among first feeders, ichthyobodosis often result in increased mortality without any obvious signs of disease. Ichthyobodosis is regarded as one of the most economically important parasitic diseases in Norwegian salmon farms. In addition to cause disease among salmonids reared in both fresh- and seawater, Ichthyobodo infections have also caused problem to marine species like cod (Gadus morhua), Atlantic halibut (Hippoglossus hippoglossus) and spotted wolfish (Anarhicas minor) in hatcheries and net pens.
For decades there has been a widespread assumption that the genus Ichthyobodo comprises only one cosmopolitan species, named Ichthyobodo necator (sensu lato. syn. Costia necatrix), but recent molecular studies have revealed that there are many species within the genus Ichthyobodo in both fresh-, brackish and seawater. More than 10 distinct Ichthyobodo species have so far been detected and indentified from wild, farmed and ornamental fish during the last years, but only 3 species have been described and named in accordance with the International code of Zoological Nomencalture (ICZN code):
1) Ichthyobodo necator (sensu stricto). Freshwater species that is able to infect salmonids and sticklebacks.
2) Ichthyobodo salmonis. An euryhaline species infecting Atlantic salmon in both freshwater and seawater. This species is probably the most common Ichthyobodo species in Norwegian salmon production.
3) Ichthyobodo hippoglossi. A marine species, so far only identified from farmed and wild caught Atlantic halibut.