Diseases, prophylaxis and treatment of the Atlantic halibut Hippoglossus hippoglossus: a review

Abstract

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...

Biodiversity of Vibrios

“…Alternatives involving more environmentally sound aquaculture have been proposed (35). Vaccination has been successfully used to control V. anguillarum and V. vulnificus infections in fish (49,124).…”

“…The pathogenic effects of certain strains of vibrios are critical in aquaculture settings, where organisms, e.g., penaeid shrimps and salmonids, are reared at high densities under very artificial and unstable conditions (14,35,295). To maintain the productivity of such an intensive aquaculture, high inputs of fish protein originating from the sea have to be employed for feeding, together with high levels of water exchange and the massive use of antibiotics.…”

“…Vibrios are important bacterial pathogens for animals reared in aquaculture (14,35,168,236). V. anguillarum, V. salmonicida, and V. vulnificus are among the main bacterial pathogens of several fish species (14), and V. harveyi is a major pathogen of shrimp, e.g., Litopenaeus vannamei and Penaeus monodon (15,225,227).…”

Distribution of Hatschekia pagellibogneravei (Copepoda: Hatschekiidae) on the gills of Pagellus bogaraveo (Teleostei: Sparidae) from Madeira, Portugal

“…Although very little is known about the life cycle of Hatschekia spp. (Bergh et al 2001), there is no reason to suppose them to be living longer than other copepod species, thus limiting their accumulation on the host over time.…”

Ichthyobodo hippoglossi n. sp. (Kinetoplastea: Prokinetoplastida: Ichthyobodonidae fam. nov.), an ectoparasitic flagellate infecting farmed Atlantic halibut Hippoglossus hippoglossus

“…Ichthyobodo sp. infections on farmed halibut have previously been reported from Scotland (Bruno & Shields, in: Bruno 1992) and Norway (Rødseth 1995, Bergh et al 2001.…”