COMPARISON OF IMPOSEX RESPONSE IN 3 PROSOBRANCH SPECIES

A comparative study of the three gastropod species Nucella lapillus (L .), Ocenebra erinacea (L.) and Hinia (Nassarius) reticulata (L.) revea ls that Nuccella is the most TBT sensitive species while Hinia is the least sensitive. Of the two imposer indices VDSI and RPSI, good inters pecies correlations were obtained only for VDSI. The three species can be considered as complementary not only in terms of their ecology but also for their levels of sensitivity. Indeed, Nucella and Ocenebra ar e useful test species at TBT concentrations below 2 ng Sn l(-1) while Hinia is the more appropriate species at higher TBT levels. For the fi rst time, two sterilised Hinia females are recorded. This sterilizatio n does not seem to be due to proliferation of vas deferens tissue in t he vaginal opening and further investigation is needed to find interme diary VDS stages between stage 4(+) and sterilization. Studies using N ucella show that the use of narcotization in imposer analysis leads to an underestimation of RPSI compared with non-narcotization methods. I ndeed, narcotization straightens the penis and increases its length wh en compared with non-narcotized animals, but this increase is proporti onally higher in males than in females.