Ovo-testis and disturbed reproductive cycle in the giant abalone, Haliotis madaka: possible linkage with organotin contamination in a site of population decline

Histological examination of gonads as well as chemical analysis of organotin compounds in tissues of the giant abalone, Haliotis madaka, was conducted to evaluate possible endocrine disruption and to consider the causal factors for the decline of abalone stocks in Japan. Abalone specimens were collected from two different areas, Tsushima as a reference site and Jogashima as a site representative of declining abalone populations, each month from September 1995 to November 1996. Scores were given to the development stages of reproductive cells in the ovary and testis. The degree of sexual maturation was evaluated by calculating the mean value of a histogram of these scores for the reproductive cells of each abalone. The temporal variations in degree of sexual maturation showed that female and male abalone from Tsushima matured synchronously, while those from Jogashima did not. The observed maximum reproductive developmental score in abalone from Jogashima was much lower than that from Tsushima, because immature females were present at the former site throughout the spawning season. Approximately 20% of the abalone from Jogashima were masculinized females with an ovo-testis. The masculinization of female abalone was similar to the imposex, typically induced in other gastropod molluscs by tributyltin (TBT) and triphenyltin (TPhT) from antifouling paints. Concentrations of TBT and TPhT in the muscles of abalone from Jogashima (n=83) of 4.9±4.4ng/g wet wt and 6.3±6.6 ng/g wet wt, respectively, were significantly higher than those from Tsushima (n=125) (P<0.01) of 0.8±0.8 ng/g wet wt and 0.6±1.3 ng/g wet wt, respectively. In situ exposure of abalone from Tsushima caged near a dockyard in Jogashima for 7 months (from the immature to the mature stage) resulted in spermatogenesis in the ovary of approximately 90% of females. Endocrine disruption may be caused in the giant abalone by organotin compounds from antifouling paints, which are possibly one of the causal factors for the decline of Japanese abalone stocks.