Hatchery-reared spat obtained from native oyster stocks was cultured. The spat was placed in baskets on rafts at 12 months of age. Bimonthly samples were taken and the presence of Bonamia, other pathological conditions and mortality were estimated

A J Figueras

Galicia

N W Spain

Ria De Vigo

CiteSeerX

Bonamia status and its effects in cultured flat oysters in the 
Ria de Vigo, Galicia (N.W. Spain) 
 
A. J. Figueras 
Instituto de Investigaciones Marinas CSIC, Vigo, Eduardo Cabello 6, 36208 Vigo, 
Spain 
 
ABSTRACT 
 
Figueras, A.J., 1991. Bonamia status and its effects in cultured flat oysters in the Ria de 
Vigo, Galicia (N.W. Spain). Aquaculture, 93: 225-233. 
 
Hatchery-reared spat obtained from native oyster stocks was cultured. The spat was 
placed in baskets on rafts at 12 months of age. Bimonthly samples were taken and the 
presence of Bonamia, other pathological conditions and mortality were estimated. 
 
INTRODUCTION 
 
Production of cultured flat oyster (Ostrea edulis) has suffered a dramatic decrease since 
1974 due to the lack of oyster spat formerly supplied by French producers. This was the 
result of a crash in their culture attributed to Marteilia refringens (Masso, 1978). This 
parasite was introduced in the same way as Bonamia ostreae in the 1980s (Figueras, 
unpublished): with the spat for culture and with the adults that were imported for human 
consumption. This has contributed to the virtual disappearance of this species in culture 
in Galicia. At present the “production” of flat oyster (Ostrea edulis) is mainly an import 
business, with little or no production of native oysters. An interesting review of the 
status of Bonamia disease has been given by Grizel et al. (1988). Mortality attributed to 
a neoplastic disorder and reaching levels of 60-80% has also been described in flat 
oysters cultured in Galicia (Alderman et al., 1977). 
 
In this paper the prevalence of Bonamia and other pathological conditions and their 
relationship with mortality rates are described. 
 
MATERIAL AND METHODS 
 
Hatchery-reared spat obtained from oyster stocks at Vigo was cultured. The spat was 
placed in baskets on rafts in Domayo (Ria de Vigo, Fig. 1) at 12 months of age. From 
May 1988 to September 1989 approximately 25 to 30 oysters were collected bimonthly, 
and mortality was estimated by counting the number of dead and live oysters from a 
total of 1500 individuals. The sampled animals were fixed in order to prepare 
histological slides to detect the presence of pathogens. After shell removal all tissues 
were fixed in Davidson’s fixative (Shaw and Battle, 1957). An anterior transverse 
section was taken including digestive gland, mantle, and gills. Histological sections 
were cut 5 pm thick and stained with iron haematoxylin, acid fuchsin and aniline blue 
(Gray, 1954). 
 
RESULTS 
 
Pathological conditions 
 
The different pathological conditions detected were Bonamia sp., ciliates in gills, 
neoplastic cells, haemocyte infiltration (Alderman et al., 1977), and aggregates of 
granulocytes (granulocytoma). 
 
At the beginning of the experiment the slightly basophilic types of Bonamia were more 
abundant. One year later, when mortalities were higher, the highly basophilic Bonamia 
types were more abundant. The “neoplastic cells” had pleomorphic or spheroid nuclei, 
and they were hypertrophied, usually enlarged to two to four times the diameters of 
normal haemocytes. 
 
Only in one animal was Marteilia refringens detected in the digestive epithelium of the 
stomach, and in oocytes of a mature oyster the microsporidian Steinhausia ovicola was 
found. 
 
There was no clear relationship between the prevalence of the different pathological 
conditions and the age of the animals (Fig. 2) .There was a notable decrease in the 
prevalence of Bonamia after 2 months on the raft. 
 
The presence of different pathological conditions in the same animal was also studied 
and is shown in Table 1. The animals that had Bonamia sp. tended also to show the 
presence of general haemocyte infiltration and the presence of granulocytomas. 
 
In Table 2 the correlations between the prevalences of different pathological conditions 
and the mortality rates and mean length are shown. 
 
Mortality 
 
The mortality was relatively “low” until the oysters were 24 months old (May 1989) 
(Fig. 3). After that, it reached almost 40% in September. There was an intriguing 
decrease in mortality in July, between the higher mortality rates registered in May and 
September (1989). 
 
There was no clear relation between the mortality rate and the pattern of growth in meat 
weight, length and total weight, although after the first peak in mortality there was a 
decrease in the mean total length, meat weight and total weight (Fig. 3). This could 
indicate that the bigger oysters die before the smaller ones. In a current experiment, 
mortality rates are being monitored taking into account the oysters with higher growth 
versus the slower growing individuals. 
 
From Fig. 4 a and b, it would seem possible to culture oysters up to commercial size 
before great losses are experienced. After 14 months of culture more than 60% of 
commercial size oysters are obtained during the best commercial season in Spain 
(December). 
 
The correlation between the different pathological conditions and the mortality during 
this period is shown in Fig. 5. It is significant for the first four conditions shown. 
 
Comparison of the mortalities caused by Bonamia in 1984 (Montes and Melendez, 
1987) and in 1988 (present study) with previous mortalities attributed to Marteilia 
refringens (Masso, 1978) shows that the virulence of Bonamia is higher (Fig. 6). 
Further studies will show if there is any trend in the decrease in mortality rates. 
 
DISCUSSION 
 
Oyster growers from Vigo have confirmed that they introduced flat oyster spat from 
Bodega Bay (California) before the mortalities attributed to Marteilia refringens began 
in Galicia. Some authors believe that the origin of Bonamia is in that part of the United 
States (Elston et al., 1986). 
 
One striking aspect of the histopathological data is the almost complete disappearance 
of Marteilia refringens which was the cause of the mortalities in cultured oysters in 
Galicia during the 1970s. Masso (1978) had already indicated the lack of correlation 
between the prevalences of Marteilia refringens and the mortalities found. This makes 
one wonder whether Marteilia was the true killer or whether some other, undescribed, 
factor was responsible. 
 
The presence of the neoplastic cells is also intriguing. Alderman et al. (1977) had 
attributed a mortality that appeared in Galicia and Yugoslavia to the presence of this 
pathological condition. These authors described what they considered to be a 
disseminated sarcoma with a proliferation of atypical haemocytic cells that developed 
into a widespread degeneration and necrosis of tissues with death of the organism. They 
also were able to induce the disease in healthy oysters by placing them near “infected” 
animals in the field. On the other hand, Grizel and Hine (pers. commun.) consider the 
presence of the so-called “neoplastic cells” to be a consequence of infection rather than 
etiological. When the animal is dying because of Bonamia, the “neoplastic cells” 
appear. More research should be focused on this part of the Bonamia syndrome, to 
determine the importance of the appearance of the “neoplastic” cells and their 
relationship with Bonamia. The correlation of the frequency of appearance of ciliates 
and Bonamia could be explained by a high Bonamia infection corresponding to a 
prephase of mortality. The good correlation between the frequency of appearance of 
Bonamia and haemocytic infiltration is explained by the reaction of the cellular defence 
mechanisms to a non-self stimulus. The data also show that the pattern of the disease 
already described in different areas of the world (Grizel et al., 1988) is again 
maintained. There are no big differences between rias. 
 
It is also possible, as with other molluscan diseases, to “manage around” the disease; in 
other words, relatively high numbers of commercial size oysters can be obtained before 
the major peak of mortality occurs. 
 
With the upcoming data on the performance of fast-growing versus slow-growing 
strains of flat oysters, more light may be shed on the cause of death of oysters with 
Bonamia. This increase in knowledge of the disease will result in better management of 
the culture of this economically important species. 
 
REFERENCES 
 
Alderman, D.J., Van Banning, P. and Perez Colomer, A., 1977. Two European oysters 
(Ostrea edulis) mortalities associated with an abnormal hemocytic condition. 
Aquaculture. 10: 340-355. 
Elston, R., Farley, C. and Kent, M., 1986. Occurrence and significance of bonamiasis in 
European flat oyster Ostrea edulis in North America. Dis. Aquat. Organisms, 2: 49-
54. 
Gray, P., 1954. The Microtomist’s Formulary and Guide. Blakiston, New York, NY, 
749 pp. 
Grizel, H., Mialhe, E., Chagot, D., Boulo, V. and Bachere, E., 1988. Bonamiasis: a 
mode1 study of diseases in marine molluscs. In: W.S. Fisher (Editor), Disease 
Processes in Marine Bivalve Molluscs. Am. Fish. Sot. Spec. Publ. No. 18, pp. l-4. 
Masso, J.M., 1978. La enfermedad de la glandula digestive de la ostra (Ostrea edulis L.) 
en las rias bajas. Bol. Inst. Esp. Oceanogr., 4: 125- 140. 
Montes, J. and Melendez. MI., 1987. Données sur la parasitose de Bonamia ostreue 
chez l’huitre plate de Galice, Cote nord-ouest de I’Espagne. Aquaculture, 67: 195-
198. 
Shaw, B.L. and Battle, H.I., 1957. The gross and microscopic anatomy of the digestive 
tract of the oyster Crassostreu virginica (Gmelin). Can. J. Zool., 35: 325-346. 
 
Fig. 1. Sites sampled in the Rias Bajas (Galicia) from 1974 to 1989. 
 
Fig. 2. Relation between age in months and the prevalences of pathological conditions 
and mortality rates. 
 
Fig. 3. Relation between the age, mortality rate and the pattern of meat weight, length 
and total weight. 
 
Fig. 4. Relation between age and the proportions of the different size (4a) and weight 
(4b) classes of marketable oysters. 
 
Fig. 5. Regressions of the prevalences of diseases and parasites and the mortality rates. 
 
Fig. 6. Comparison of the mortalities attributed to Bonamia in the 1980s with previous 
mortalities attributed to Marteilia refrringens 
 
TABLE I 
Correlation between the different pathological conditions appearing in the same animal: 
Spearman rank correlation 
 
TABLE 2 
Correlations between the prevalences of different pathological conditions and the 
monthly mortality rate and mean length: Pearson product-moment correlation 
 
Table 1 
 SEX  INFILT.  GRAN. BONAM. CILIAT. NEOPL.  AGE 
SEX  1.000       
INFILT.  0.186 1 .000      
GRAN.  0.037  0.447  1.000     
BONAM.  0.005  0.517*  0.440*  1.000    
CILIAT.  0.008  0.170  0.026  0.138  1.000   
NEOPL.  0.200  0.231  0.199  0.248  0.112  1 .000  
AGE  0.183  0.318  0.101  0.336  0.270  0.298  1.000 
*Significant correlation. 
INFILT. = haemocytic infiltration; GRAN. = granuloma; BONAM. = Bonamia; 
CILIAT. = ciliates; NEOPL. = neoplastic cells. 
 
 
Table 2 
 % 
Bonam.  
% 
Infiltr.  
% 
Ciliates  
% 
Neopl.  
% 
Granul.  
Mortality  Mean 
length 
% Bonam.  1.000       
% Inliltr.  0.905*  1 .000      
% Ciliates  0.682*  0.786*  1.000     
% Neopl.  0.551  0.593  0.676*  1.000    
% Granul.  0.791*  0.522  0.164  0.240  1.000   
Mortality  0.742*  0.846*  0.876*  0.599  0.105  1.000  
Mean 
length  
0.454  0.608  0.674  0.763* 0.361 0.276 1.000 
*Significant correlation. 
% Bonam. = prevalence of Bonamia; % Infiltr. = prevalence of haemocytic infiltration; 
% Ciliates = prevalence of ciliates; % Neopl. = prevalence of neoplastic cells; % 
Granul. = prevalence of granulocytoma; Mortality = mortality rate. 


Bonamia status and its effects in cultured flat oysters in the

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=6E7E9DAE9481917F2B4E41DD34A1FF11?doi=10.1.1.1048.7876&rep=rep1&type=pdf

Bonamia status and its effects in cultured flat oysters in the

Abstract

Similar works

Full text

Available Versions

CiteSeerX