A. Villalba et al., SYMBIONTS AND DISEASES OF FARMED MUSSELS MYTILUS-GALLOPROVINCIALIS THROUGHOUT THE CULTURE PROCESS IN THE RIAS OF GALICIA (NW SPAIN), Diseases of aquatic organisms, 31(2), 1997, pp. 127-139
Mediterranean mussels Mytilus galloprovincialis were experimentally cu
ltured from 5 rafts located in 4 Galician Rias, following the establis
hed industrial procedure. Cultures were sampled monthly until mussels
exceeded market size. Observation of histological sections of sampled
mussels by light microscopy demonstrated symbionts which could be clas
sified into 3 groups according to their pathogenicity. The first group
consisted of symbionts with unnoticeable pathogenic effects including
: prokaryotic inclusion bodies (PIE) in digestive gland and gills, an
unidentified protistan in digestive primary ducts, a kidney coccidian,
intracytoplasmic ciliates in digestive tubules, gill ciliates and a t
urbellarian in the intestinal lumen. The second group comprised symbio
nts that could damage the host, although unlikely to be lethal, includ
ing: the microsporidian Steinhausia mytilovum, the flatworm Urastoma c
yprinae, and the copepod Mytilicola intestinalis. The third group incl
uded the protistan Marteilia refringens and the trematode Proctoeces m
aculatus, potentially lethal pathogens. In addition, mussels with haem
ocytic infiltration of tissues and granulocytomas and a few cases of d
isseminated neoplasia were detected. The qualitative composition of mu
ssel symbiont community was similar at the 5 study sites, except for 3
symbionts which were not detected at some sites. Quantitatively, symb
iont loads were higher and histological signs of stress more abundant
in Moana and Vilagarcia (the most inner sites in the Rias), intermedia
te in Illa de Arousa and Muros, and lower in Lorbe. Symbionts increase
d in prevalence as mussels grew. Some of the symbionts were detected i
n mussel seed at the beginning of the experimental cultures.