Fish health and disease - grouper

Bondad-Reantaso, Kanchanakhan and Chinabut (2001) presented a review of the diseases affecting cultured groupers in SE Asia, which listed the various grouper species affected, together with the symptoms, and the country where the infection was found. The contents of this section of the report are principally drawn from that source. A summary of the major pathogens reported to have affected farmed groupers is given in Table 40.

Gram-negative bacteria, ectoparasitic protozoans and monogeneans are among the most important pathogens for groupers. The lethal “sleepy grouper disease”, seen in Singapore, was probably caused by a virus introduced with wild juvenile groupers that had been imported for cage farming (Tucker 1999). Other viral pathogens and diseases include “golden eye disease”, “red grouper retro-virus”, “spinning grouper disease”, and “viral nervous necrosis”. Pasteurellosis has been a major disease in young red-spotted groupers in Japan. Infestations of the gills, eyes and skin by monogenean or protozoan parasites, which feed on blood, skin and mucus have been reported for Western North Atlantic species (Tucker 1999).

The most common disease encountered in captive groupers is “red boil disease” characterized by inflammation, haemorrhage and ulceration of skin and musculature. Infection by the protozoan parasite Cryptocaryon irritans causes loss of scales and skin, especially in the head region (Pillay 1995; Bondad-Reantaso, Kanchanakhan and Chinabut 2001). Chou et al. (1999) found a positive correlation between increased environmental stress (transport, crowding, temperature and catching stresses, and exposure to heavy metal pollutants) and increased mortality; this correlation has also been documented in cases involving infectious haematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV).
A new grouper infection, caused by a marine leech (Zeylanicobdella arugamensis), has been documented in the Philippines, Sri Lanka, the Malay Peninsula, Singapore, India, Indonesia and along the coast of Queensland, Australia (Cruz-Lacierda et al. 2000). A didymozoid trematode (Gonapodasmius epinepheli) infection was also observed in pond-reared orange-spotted grouper (E. coioides) in the Philippines. Didymozoids are parasitic trematodes, usually living in pairs of capsules in the connective tissue of the fins, skin, mouth cavity, operculum, muscles, stomach, intestine, liver or other organs of fish (Cruz-Lacierda et al. 2001).

Table 40. Specific pathogens of cultured groupers in Southeast Asia
VIRUSES
Nodaviruses
? Viral Nervous Necrosis (VNN)
? Spinning grouper disease
? Paralytic syndrome
Iridoviruses
? Sleepy grouper disease
? GIV-1
? GIV-2
? Blister disease
Reovirus
? Red grouper disease
Astro-like virus
? Golden eye disease
? Lymphocystis
? Herpes virus
BACTERIA
? Bacteriosis caused by Pseudomonas sp.
? Pasteurella piscicida
? Red boil disease
? Flexibacter sp.
? Vibrio spp.
? Vibrio harveyi
? Vibrio parahaemolyticus
PARASITES
Protozoa
? Brooklynella sp.
? Cryptobia sp.
? Cryptocaryon irritans
? Ribosyphidia sp.
? Scyphidia sp.
? Trichodina sp.
? Vorticella sp.
Myxozoa
? Myxosoma sp.
? Ceratomyxa sp.
? Sphaerospora sp.
Microspora
? Pleistophora sp.
4 - GROUPERS 97
Monogenea
? Benedenia sp.
? B. ephinepheli
? Cycloplectanum epinepheli ? Dactylogyrus sp.
? Gyrodactylus sp.
? Haliotrema sp.
? Neobenedenia girellae ? Megacotyloides epenepheli ? Megacotyloides sp.
? Tareenia sp.
? Diplectanum sp.
? Pseudorhabdosynochus sp. ? Dactylogyridae
? Diplectanidae
Trematoda
? Allopodocotyle sp.
? Cardicola
? Ectenurus sp.
? Gonapodasmius sp.
? Helicometrina nimia
? Lecithochirium neopacificum ? Pearsonellum sp.
? Prosorhynchus pacificus ? Prosorhynchus sp.
? Pseudopecoeloides sp. ? Pseudometadena celebesensis ? Stephanostomum sp.
? Didymozidae
Crustacea
? Caligus sp.
? Ergasilus borneoensis
? Gnathia sp.
? Lepeoptheirus sp.
? Thebius sp.
Nematoda
? Contracaecum sp.
? Echinocephalus sp.
? Raphidascaris sp.
Cestoda
? Tetraphyllidae
? Cestoda sp.
Achantocephala
? Acanthocephalus sp.
Hirudinea

Apart from some virus problems in Southeast Asia, very little is known about the impact of major diseases, which may go beyond the direct effects of observed mortalities and production losses. Disease outbreaks, and the subsequent losses they create, affect all levels of aquaculture activity and are profoundly felt by small-scale farmers, who represent the backbone of many rural communities. In Asian aquaculture, the livelihoods of farmers are threatened through reduction in food availability, loss of income and employment, social upheaval and increased vulnerability (Bondad-Reantaso, Kanchanakhan and Chinabut 2001).