Imposex in Thais clavigera (neogastropoda) as an indicator of TBT (tributyltin) bioavailability in coastal waters of Hong Kong

The degree of imposer (the imposition of male characteristics onto females) exhibited by females of Thais clavigera, collected during August 1996, was assessed using the Relative Penis Size Index (RPSI) and the Vas Deferens d evelopment sequence (VDS), to ascertain the extent of TBT (tributyltin) bio availability in Hong Kong's coastal waters. All sites showed some degree of imposer development. The most affected areas were Victoria Harbour and Abe rdeen where up to 92% of females were effectively sterilised by the develop ment of a vas deferens, thereby, blocking the oviduct (VDS scores of 4-6 an d RPSI of 32-41%). There is some evidence of this affecting the population structure of T. clavigera, i.e., a dominance of males in affected populatio ns. A Tolo Harbour site, at Starfish Bay, remote from major shipping routes was the least affected having an 88% incidence of imposer (VDS scores of 0 -2 and RPSI of <0.1%).