AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS Aquatic Conserv: Mar. Freshw. Ecosyst. 19: 797–805 (2009) Published online 26 March 2009 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/aqc.1028 Growth and reproduction of threatened native crucian carp Carassius carassius in small ponds of Epping Forest, south-east England ALI SERHAN TARKAN a,b , GORDON H. COPP a,c,Ã , GRZEGORZ ZIE ˛ BA a,d , MICHAEL J. GODARD a and JULIEN CUCHEROUSSET a,c a Salmon & Freshwater Team, Centre for Environment, Fisheries & Aquaculture Science, Pakefield Road, Lowestoft, Suffolk, NR33 0HT, UK b Mug ˘la Universitesi, Su Urunleri Fakultesi, 48000, Ko ¨tekli, Mug ˘la, Turkey c School of Conservation Sciences, Bournemouth University, Dorset House, Talbot Campus, Fern Barrow, Poole, Dorset BH12 5BB, UK d Department of Ecology & Vertebrate Zoology, University of Lo ´dz´, Banacha 12/16, 90-237 Lo ´dz´, Poland ABSTRACT 1. The crucian carp Carassius carassius is a species of cyprinid fish native to south-east England, but few studies exist on its growth and reproduction in England, and the species is threatened by introductions of its Asiatic congener, goldfish Carassius auratus. To increase knowledge of the crucian carp as a means of aiding its conservation, the present study assesses the growth (back-calculated length at age, body condition) and reproduction (fecundity, egg size, length and age at maturity) of crucian carp in small ponds of Epping Forest (north-east London, England). 2. Evaluation of growth and reproduction data with published data for populations from northern Europe (i.e. latitude X501) suggest that growth is very variable, even within the same area, and that data on reproductive indices, in particular length and age at maturity, are scarce. In England, the length at age trajectory of crucian carp living in sympatry with feral goldfish Carassius auratus did not differ significantly from allopatric crucian carp populations, but crucian carp body condition and relative fecundity (eggs per body weight) were highest, and mean age and standard length at maturity were lowest in sympatry with goldfish. 3. These data suggest that somatic growth and reproductive output may be maximized in crucian carp when confronted by coexistence with feral goldfish. However, the potential impact of goldfish introductions on crucian carp growth and reproduction requires further study, involving a much larger number of crucian carp populations, both in allopatry and sympatry with feral goldfish populations. r Crown copyright 2009. Reproduced with the permission of Her Majesty’s stationery Office. Published by John Wiley & Sons, Ltd. Received 14 July 2008; Revised 17 December 2008; Accepted 10 January 2009 KEY WORDS: endangered species conservation; sympatric compensatory growth; feral goldfish; illegal releases; acclimatization INTRODUCTION One of the less-well studied of the fish species native to parts of the British Isles is the crucian carp Carassius carassius. Indeed, until the recent papers by Copp et al. (2008a,b), the only known study of crucian carp biology in England was that of Marlborough (1967). The crucian carp was previously classed as non-native to the British Isles (Maitland, 1972), believed to have been introduced along with the common carp Cyprinus carpio in the late 15th century. However, the crucian carp was re-classified by Wheeler (1977) as native to south-east England for two reasons: (1) crucian carp pharyngeal bones were found in an archaeological site from the Roman period, which pre- dates the known introduction of common carp in the 14th *Correspondence to: G.H. Copp, Salmon & Freshwater Team, Centre for Environment, Fisheries & Aquaculture Science, Pakefield Road, Lowestoft, Suffolk, NR33 0HT, UK. E-mail: gordon.copp@cefas.co.uk r Crown copyright 2009. Reproduced with the permission of Her Majesty’s Stationery Office. Published by John Wiley & Sons, Ltd.