Chromosomal study of spatial variation of the prevalence of a gill neoplasia inMacoma balthica(L.) from the Gulf of Gdansk (Baltic Sea)

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Abstract
Spatial variation of the prevalence of a gill neoplasia in the bivalve Macoma balthica was investigated by chromosomal study of individuals from ten different sites in the Gulf of Gdansk. The prevalence of gill neoplasia, individually identified by the occurrence of abnormal metaphases with higher chromosome numbers than normal metaphases (2n = 38), ranges from 0 to 94% of individuals, according to the site studied. Sites Hel 45 m and Vistula 30 m, located in the zone of the thermocline and halocline were the most affected, probably related to very unstable hydrological conditions at these sites. Out of a total of 152 animals studied from the Gulf of Gdansk, 33% showed the occurrence of gill neoplasia. A chromosome number from 59 to 109 was scored in 29 abnormal metaphases. Karyotypes were constructed from 14 abnormal metaphases and showed a similar general pattern. This study showed that chromosomal abnormalities involving numerical and morphological changes imply similar disorders among the sites studied. Etiology of this disease is still unknown but the seriously polluted Gulf of Gdansk can be used as a model basin to assess the relationship between the incidence of neoplasia and the possible controlling factors of environmental instability and/or level of environmental contaminants.