After substantial investments in research, the Atlantic halibut Hippoglossus hippoglossus is now being cultivated commercially in Norway, Iceland, Scotland and Canada. As with other domesticated species, disease problems have been experienced. This review summarizes the current state of knowledge of diseases of the Atlantic halibut, and their diagnosis, prophylaxis and treatment. In economic terms, the most important losses have been suffered at the larval and juvenile stages. The most important infections are caused by nodaviruses, causative agents of Viral Encephalopathy and Retinopathy (VER), which are the major reason why Norway's production of halibut fry has been level since 1995. An aquatic birnavirus, Infectious Pancreatic Necrosis Virus, is also an important agent of mortality. Vibrio anguillarum, Flexibacter ovolyticus and atypical Aeromonas salmonicida are the major bacterial pathogens. The protozoan parasites recorded include Ichthyobodo sp., the microsporidium Enterocytozoon sp., Trichodina hippoglossi, and the metazoan pathogens include myxozoans, helminths, Entobdella hippoglossi, Lepeophtheirus hippoglossi and other parasitic copepods. Experimental vaccines have been tested against V. anguillarum and atypical A. salmonicida, with good results. A recombinant vaccine against nodaviruses is under development. A few trials have been carried out on non-specific immunostimulants, but no such treatment is currently available. A number of efficacy and pharmacokinetic trials with various antibacterial agents have also been published.
KEY WORDS: Atlantic halibut · Diseases · Prophylaxis · Treatment
Resale or republication not permitted without written consent of the publisherDis Aquat Org 48: [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74] 2001 unknown may accidentally compromise the defence systems of the host. Thirdly, disease conditions that may be common among wild fish are largely unrecognised by humans. However, in aquaculture systems the fish farmer will recognise signs of disease such as reduced growth, abnormal behaviour and increased mortality, all of which rapidly call for attention by veterinarians and scientists.The main challenge experienced by halibut farms has been to achieve adequate survival rates, particularly during the early life stages. Thus, since the early 1990s, the amount of experience and knowledge of diseases of viral, bacterial or parasitical etiology of the Atlantic halibut has grown significantly. The evidence for the importance of diseases that affect the early life stages, such as infections by birnaviruses (Biering et al. 1994), nodaviruses (Grotmol et al. 1995(Grotmol et al. , 1997, or various opportunistic bacteria (Bergh et al. 1992b) has now been demonstrated by different challenge experiments (Table 1).The parasite fauna of wild Atlantic halibut have not been widely studied, for which reason our knowledge of potential harmful parasites in farmed fish is limited. Studies of parasites on wild halibut have mainly concentrated on desc...