A Review of Ichthyobodo Necator (Henneguy, 1883) an Important and Damaging Fish Parasite

Abstract

Ichthyobodo necator or Costia necatrix as it is more commonly known is a very important protozoan parasite of cultured fish throughout the world. Its importance is often underestimated in the scientific literature probably because it is so often missed by scientists and fish farmers alike because of its small size and transparency when observed in the normal light microscope. However, it is probably the major cause of death of cultured salmonid fry in Scottish fish farms; even the viral disease IPN seldom causes such acute mortality as does Ichthyobodo. Because of its predilection for first feeding fry salmonid farmers generally assume that an Ichthyobodo infection is extant before investigating other possible causes and thus excessive treatment with formalin, often unnecessarily, is the norm in most farms. For such an economically important parasite it is surprising that there has been relatively little research carried out on aspects of its biology. Much of the literature on Ichthyobodo was published in the first half of the twentieth century and concentrated on trying to establish the taxonomic status of the parasite. Other reports of Ichthyobodo in the literature briefly mention the parasite in species lists for infestations of groups of fish or in parasite lists for specific countries.