The Most Economically Important
Pathologies of the
Marine Fish Cultured in Greece and the Aegean Sea
|
Presentation by Dr. Panos Varvarigos at the 10th National Conference
of the Italian Society of Fish Pathologists |
|
CONTENTS |
Copyright (c) Dr Panos
Varvarigos
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reproduction of this website (or parts of it) is illegal and strictly
forbidden.
No rights can be derived from this website.
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 economically damaging
pathologies are still surprisingly few.
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).
Among the
viral diseases, viral encephalopathy and retinopathy (VER) or viral nervous
necrosis (VNN) of sea bass (Nodavirus) causes
excessive damage to all ages of bass. Other viral diseases, such as lympocystis of sea bream , caused by
lympocystis Iridoviruses
are not underestimated in this presentation, but the losses associated with
them are not considered severe.
Most endo-parasitic diseases are not considered yet of critical
economic importance with the exception of a myxosporidiosis
of sharp snout bream as well as sea bream caused by Enteromyxum
leei, affecting the gastrointestinal tract (enteromyxosis). Nevertheless, another sea bream endoparasitic myxosporean, Polysporoplasma sparis, is gaining
importance affecting the kidney and causing polysporoplasmosis.
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).
On the other
hand, young fish in hatcheries suffer skeletal and fin deformities, with poorly
understood aetiology. Although it is debatable whether anatomic disorders
comprise the outcome of some pathogen, malnutrition or of man-made adverse
environment, the fact remains that discarded, deformed fish comprise a serious
cost element of hatchery production.
Diseases of frequent occurrence but of moderate
economic bearing comprise other bacterial 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.
The lymphocystis viruses (Iridoviridae), which affect young bream, have rather
indirect consequences by weakening the fish and predisposing to other
pathologies.
Usual ecto-parasites found on the gills of the
farmed fish, but of unquantified economic
implications, comprise the common metazoan flatworms of the order Monogenea (either Monopisthocotylea
or Polyopisthocotylea). Gill cryptocaryoniasis
and amyloodiniasis are rare in the region and are
diagnosed occasionally in brood-stock fish.
Still unspecified, but rather moderate, is the damage to health and fish
growth of most endo-parasites belonging to the class Myxosporea (other than Enteromyxum)
causing myxosporidiosis (sphaerosporosis,
polysporoplasmosis, ceratomyxosis).
Similarly, 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.).
Last, the 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.
Many other isolated diseases
attributed mainly to parasites, bacteria and fungi as well as man-made problems
(management, water quality), are diagnosed sporadically, but do not seem to
constitute common threats for the farmed fish as yet.
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).
Licensed antibiotics against bacterial pathogens are only a few. Vaccines
against vibriosis and pasteurellosis
have been licensed, but protection against pasteurellosis
conferred by the available vaccines is limited and short-lived. There is no
vaccine against VNN yet. On the other hand, simple common sense management
measures, such as regular disinfection, cage-net washing, avoiding
over-crowding and over-feeding of the fish, combined with deep waters with
sufficient currents have proved invaluable to many farms.
The most economically
important diseases
|
Frequent occurrence with high losses/costs |
Bacterial septicaemias |
|
Occasional incidents but with high losses/costs |
Viral diseases |
Copyright (c) Dr Panos
Varvarigos
All rights reserved,
reproduction of this website (or parts of it) is illegal and strictly
forbidden.
No rights can be derived from this website.
