IMPOSEX IN SUBLITTORAL AND LITTORAL GASTROPODS FROM THE GULF-OF-THAILAND AND STRAIT OF MALACCA IN RELATION TO SHIPPING

The study aimed to survey the presence and extent of imposer in sublit toral gastropods in relation to shipping traffic in the Gulf of Thaila nd and the Strait of Malacca. Females of several species of meso- and neogastropods showed a high-incidence (up to 100%) of imposer at sever al sites. These females had a penis of variable size and a vas deferen s (sperm duct), two typically male characteristics. Imposer has been f ound to be caused by TBT from antifouling paints. The occurrence of im poser was related to the distance to the main shipping routes, but not to water depth or diet of the investigated gastropods. TBT remains ac tive far away from the target area and influences non-target animals. Some gastropods affected by imposer were found within shellfish cultur e plots and on the fish markets.