Economically
Important Pathologies of the
Marine Fish Cultured in Greece and the Aegean Sea
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Based on the presentation by Dr. Panos Varvarigos at the 10th National Conference of
the Italian Society of Fish Pathologists 9-11 October 2003 |
Copyright (c) Dr. Panos Varvarigos.
AquaHealthTM
Laboratory.
Reproduction
of this website (or parts of it) is illegal and strictly forbidden.
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The major marine fish
grown in the Eastern Mediterranean basin are sea bass (Dicentrarchus
labrax, family Serranidae)
and sea bream (Sparus auratus,
family Sparidae). Additional species enter
intensive farming at an increasing rate. These belong mainly to the family Sparidae (breams), such as sharp snout bream (Diplodus puntazzo), white
bream (Diplodus sargus),
striped bream (Lithognathus mormyrus),
red porgy (Pagrus pagrus),
pandora (Pagellus erythrinus) as well
as dentex (Dentex dentex).
More recently, Dover
sole (Solea solea) and
meagre (Argyrosomus regius)
are successfully hatched and grown.
The contribution of all these alternative
species to the total farmed output, as compared to sea bass and sea bream
production, remains marginal, but is expected to increase in line with the
accumulation of research experience, nutrition and stock management know-how.
The production challenges of the industry relate to stock management and
welfare, application of new technologies, environment protection, fish
nutrition, disease prevention and control (fish health management).
Bacterial, viral and parasitic diseases are caused often by relatively
poorly studied pathogens that are common across the warm Mediterranean waters.
The severity of infection and hence mortality and the associated treatment cost
is usually fish size, farm site (and management) and water temperature (season)
dependent. Nevertheless, despite the intensification of production, the
prevailing damaging pathologies are still few.
BACTERIA
The most frequent, widespread, deadly and economically
important bacterial fish pathogens are Vibrio anguillarum
causing vibriosis to sea bass, and Photobacterium damsela subsp. piscicida (Pasteurella
piscicida) causing pasteurellosis (or pseudotuberculosis) to both sea bass and bream (plus many
of the new entrants to aquaculture).
Other bacterial diseases of frequent occurrence but of moderate economic
bearing comprise those septicaemias caused by several strains of vibrio (Vibrio vulnificus, V. alginolyticus),
cytophaga like filamentous bacteria (Flexibacter
spp., Tenacibaculum spp., Flavobacterium spp.),
as well as strains of motile aeromonads (Aeromonas
hydrophila, A. sobria), photobacteria
(Photobacterium damselae) and staphylococci. Most of these bacterial
infections occur more frequently in hatcheries after omissions in hygiene or
larval nutrition.
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VIRUSES
Among the viral diseases, viral encephalopathy and retinopathy (VER) or
viral nervous necrosis (VNN) of sea bass (piscine beta Nodavirus) causes
excessive damage to all ages of bass. Lympocystis of
sea bream, caused by lympocystis Iridoviruses should not be underestimated, but often the
losses associated with it are not severe. The lymphocystis
viruses affect young bream and have rather indirect consequences by weakening
the fish and predisposing to other pathologies. Nonetheless, lymphocystis produces appalling skin lesions and is
economically damaging to fry suppliers.
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ENDO- PARASITES
Most endo-parasitic diseases
are caused by parasites belonging to the class Myxosporea.
Myxosporidioses (sphaerosporosis, polysporoplasmosis,
ceratomyxosis). produce
non-quantified, but rather moderate damage to fish health and growth and are
not considered of critical economic importance with the exception of enteromyxosis. The latter is a myxosporidiosis
of sharp snout bream as well as sea bream caused by Enteromyxum
leei, affecting the gastrointestinal tract. Another
endoparasitic myxosporean, Polysporoplasma sparis, is gaining
importance affecting the kidney and causing polysporoplasmosis
to sea bream.
Mild but not precisely studied is the consequence of the
gut endo-parasitism by protozoa of the subclass Coccidia causing coccidiosis
(Goussia spp., Eimeria
spp.).
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ECTO- PARASITES
Among the ecto-parasites,
the cymothoid isopod Ceratothoa
oestroides usually infests sea bass and bream
reared in net cages. Apart from fry mortality, the isopods provoke growth
retardation and devalue the end product (isopodosis).
Usual ecto-parasites commonly found on the gills of all farmed
fish species, comprise the common metazoan flatworms of the order Monogenea (either Monopisthocotylea
or Polyopisthocotylea). The most detrimental among
these gill monogenetic trematodes (flukes) are the haematophagus species Sparicotyle chrysophrii infesting sea bream gills
and Sciaenocotyle panceri found
attached on the gills of meagre. Intense haematophagy
results in chronic anaemia, growth stunning, skin discolouration and
ulceration, liver and myocardium damage, ascites and
eventually death of the host.
Gill cryptocaryoniasis and amyloodiniasis
are rare in the region and are diagnosed occasionally in brood-stock fish.
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NON-INFECTIOUS
Non-infectious diseases comprise skeletal and fin
deformities with poorly understood aetiology. Although it is debatable whether
anatomic disorders are due to malnutrition or of man-made adverse environment,
the fact remains that discarded, deformed fish comprise a serious cost element
of hatchery production.
Winter (or Spring) syndrome manifests itself on sea bream after
exceptionally cold winters with variable losses among bream. It is believed to
result from metabolic imbalance and immuno-suppression
caused at sea temperatures below 14°C.
Chronic copper toxicity results from the prolonged exposure to elevated
copper and copper compound levels in sea water. Copper oxides comprise the
active compound contained in net antifoulants.
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Treating infectious diseases is not always feasible, or economically
acceptable in practice, nor always environmentally compatible. For example,
there are no suitable drugs against endo-parasites,
whereas knowledge gaps exist in the environmental compatibility of most antiparasitic bath treatments (formalin baths, antilouse baths with pyrethroids
and organophosphates). Licensed antibiotics against bacterial pathogens are
only few. Vaccines against vibriosis and pasteurellosis have been licensed, but protection against pasteurellosis is limited and short-lived. There is no
vaccine against VNN as yet. On the other hand, simple common sense management
measures, such as regular disinfection, clean net maintenance, avoiding
over-crowding and over-feeding of the fish, combined with deep waters with
sufficient currents ensure stock welfare and enhance natural resistance to
pathogens.
Author:
Dr. Panos Varvarigos
Freelance
Veterinarian - Fish Pathologist, Athens, Greece.
AquaHealthTM
Laboratory.
Reproduction
of this website (or parts of it) is illegal and strictly forbidden.
No rights can be derived from this website.
Disclaimer:
Every effort has been made to ensure that the
information is accurate until the date of last editing. It is based upon the
accumulated personal experience of applied veterinary work. The author cannot
take responsibility for incorrect interpretation or any resulting consequences.
The contents may be used as an educational guide and are definitely not meant
to become a stand-alone diagnostic tool or operations manual.
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