Imposex in Babylonia spirata (Gastropoda: Babyloniidae) from Pakistan (Northern Arabian Sea)

This is the first report of the occurrence of imposex in the neogastropod Babylonia spirata (Linnaeus, 1758) from Pakistani waters. Studies were carried out at Manora Channel, which is situated in the vicinity of Karachi port and fish harbor, the hub of commercial boating activity in Pakistan. Other two sites Buleji and Sonmiani are free of such activity and were therefore considered as reference sites. Specimens of B. spirata were morphologically and histologically examined. Specimens showing imposex were only found at Manora Channel. Incidence of imposex was 73.7% and the vas deferens sequence (VDS) were ranked to be between 1 to 4+. The average VDSI was 0.42 whereas the average relative penis length index (RPLI) was 14.45 and the relative penis size index (RPSI) was 0.32. Both normal and imposex females generally showed normal gonadal development. However, evidence of an ovo-testis was found in histological sections of normal and imposexed female of B: spirata gonads examined from Manora Channel. At Manora Channel the sex ratio was significantly in favour of females whereas at Buleji and Sonmiani, it was close to unity (1:1).