Life-history characteristics of an age-validated established invasive African sharptooth catfish, Clarias gariepinus, population in a warm–temperate African impoundment Reece Wartenberg 1 , Olaf L.F. Weyl 2,3* , Anthony J. Booth 1 & Henning Winker 4 1 Department of Ichthyology and Fisheries Science, Rhodes University, P.O. Box 94, Grahamstown, 6140 South Africa 2 South African Institute for Aquatic Biodiversity (SAIAB), Private Bag 1015, Grahamstown, 6140 South Africa 3 Centre for Invasion Biology, SAIAB, Private Bag 1015, Grahamstown, 6140 South Africa 4 Biological Sciences, University of Cape Town, Private Bag X3, Rondebosch, 7700 South Africa Received 29 May 2013. Accepted 10 September 2013 It has been suggested that the invasive, omnivorous Clarias garipienus is capable of rapid invasions and long-term persistence in recently inhabited freshwater systems. To test this hypothesis, the life history of the established, extralimital Darlington Dam (33°10’31”S, 25°09’13”E) population was investigated. By counting post-fluorescent mark increments on otoliths from 21 chemically tagged wild fish recaptured 244–537 days later, the deposition of growth zones, comprising alternating opaque and translucent bands, was validated as annual. Examination of sectioned otoliths from 175 fish revealed that the oldest fish, two males of 840 and 1074 mm total length (TL), were 25 years old – 10 years older than previously described for any C. gariepinus population. The oldest female was 885 mm TL and 21 years old. Length- at-age was subsequently described using the von Bertalanffy growth model. Combined-sex growth was best described as L t = 931.7 ( 1 – exp(–0.15(t+2.43))) mm TL. Total mortality (Z) was calculated using catch curve analysis and the Chapman & Robson estimator to be 0.35/yr. The presence of specimens 15 years and older indicates that these fish established quickly and supports the finding that mortality rates are low, which, in turn, suggests likely long-term population persistence. Key words:annulus validation, von Bertalanffy, mortality, longevity. INTRODUCTION African sharptooth catfish Clarias gariepinus (Burchell, 1822) is a widely distributed fish that has now invaded water bodies in South America, Eastern Europe, Asia and South Africa (Cambray 2003). In South Africa it is native as far south as the Orange-Vaal river system, but inter-basin water transfer schemes (IBWTs), illegal stocking by anglers and from aquaculture has resulted in the establish- ment of extralimital populations in almost all river systems (van Rensburg et al. 2011). Within the Eastern Cape Province, C. gariepinus has invaded the Great Fish and Sundays rivers through IBWTs, that connect the Orange River to the Great Fish River and then to the Sundays River system which flows directly into Darlington Dam (Kadye & Booth 2013a) (Fig. 1). Soon after the completion of the IBWTs sharptooth catfish were recorded in Grassridge Dam in 1976 (Laurenson & Hocutt 1985), and later from Darlington Dam in 1981 (Scott et al. 2006). Although Cambray & Jubb (1977) are of the opinion that the species was translocated prior to the IBWT connection, there is now a perma- nent corridor between the Orange River and its receiving river systems that can facilitate the con- tinued introduction of non-native Orange River fishes and other aquatic biota. There is concern that highly mobile, large and omnivorous fishes, such as C. gariepinus, can nega- tively impact native fish communities (Kadye & Booth 2012a,b, 2013a,b). Understanding the biol- ogy of C. gariepinus in invaded environments is therefore important for determining its potential impacts and future invasions. While our under- standing of its potential impacts is improving (Kadye & Booth 2012a,b, 2013a,b) there have been few life history studies within its extralimital distribution range. The objective of this study was to evaluate the long-term establishment success of African Zoology 48(2): 318–325 (October 2013) *Author for correspondence. E-mail: o.weyl@saiab.ac.za