Sensitivity of different biological responses to accumulation and depuration of butyltins in the neogastropod Thais clavigera: implications for biomonitoring Ka Ming Chan Æ Siu-Gin Cheung Æ Zongwei Cai Æ Jian-Wen Qiu Accepted: 14 July 2008 / Published online: 25 July 2008 Ó Springer Science+Business Media, LLC 2008 Abstract We conducted a 3-month reciprocal transplant of the neogastropod Thais clavigera in cages between a site heavily contaminated with tributyltin and a relatively clean site to compare the sensitivity of its reproductive and physiological responses to accumulation and depuration of butyltins. Transplanting T. clavigera from the relatively clean site to the contaminated site resulted in a higher butyltin tissue concentration, higher relative penis size index (RPSI), as well as lower scope for growth (SFG) and lower Oxygen : Nitrogen (O:N) ratio. Nevertheless, growth and vas deferens sequence index (VDSI) were unaffected. Transplanting T. clavigera from the contaminated site to the relatively clean site resulted in a significant decline in tissue burden of butyltins and an elevation of scope for growth (SFG) and O:N ratio; however, there were no marked changes in growth, RPSI or VDSI. Our results thus indicated that growth is not sensitive enough for use in short-term transplant study, SFG and O:N ratio can be used as sensitive biomarkers of both accumulation and depura- tion of butyltins, whereas RPSI can be used only as a biomarker of accumulation of butyltins. Keywords Neogastropod  Butyltin  Scope for growth  O:N ratio  Imposex Introduction Biomonitoring is an important tool in environmental assessment because it can establish causal relationship between exposure to chemical contamination and adverse biological effects (Connell et al. 1999). Many marine biomonitoring programs are designed to detect trends in short temporal scales (i.e. several months to one year), which demand the use of sensitive biological responses (Salazar and Salazar 1995; Shindo and Otsuki 1999; Rome ´o et al. 2003; The ´bault et al. 2005). Growth, scope for growth (SFG), and oxygen: nitrogen (O:N) ratio are commonly used biological responses (Con- nell et al. 1999). Growth reflects the fitness of an individual organism and has an important impact on the sustainability of natural populations (Connell et al. 1999; Shumway and Parsons 2006). Scope for growth reflects the balance between energy intake and energy expenditure (Widdows et al. 1997; Shumway and Parsons 2006), and is an inte- gration of several key physiological responses, such as respiration rate, excretion rate, ingestion rate, clearance rate, and absorption efficiency. It is a proxy of fitness because a positive value indicates that energy is available for growth, maintenance and reproduction; whereas a negative value indicates that the body energy reserve must be utilized to maintain basic life processes. The ratio between oxygen consumption and nitrogen excretion (O:N ratio) is a measure of the relative utilization of protein in energy metabolism (Stickle and Bayne 1982). A low O:N ratio indicates a high rate of protein catabolism relative to carbohydrate and lipid, and is indicative of a stressed condition (Gao et al. 2002). K. M. Chan  J.-W. Qiu (&) Department of Biology, Hong Kong Baptist University, Hong Kong, People’s Republic of China e-mail: qiujw@hkbu.edu.hk S.-G. Cheung Department of Biology and Chemistry, City University of Hong Kong, Hong Kong, People’s Republic of China Z. Cai Department of Chemistry, Hong Kong Baptist University, Hong Kong, People’s Republic of China 123 Ecotoxicology (2008) 17:860–868 DOI 10.1007/s10646-008-0249-2