157 Bol. Inst. Esp. Oceanogr. 16 (1-4). 2000: 157-165 BOLETÍN. INSTITUTO ESPAÑOL DE OCEANOGRAFÍA ISSN: 0074-0195 © Ministerio de Agricultura, Pesca y Alimentación, 2000 Restoration of Acipenser sturio L., 1758 in Germany: Growth characteristics of juvenile fish reared under experimental indoor conditions F. Kirschbaum 1 , J. Gessner 1 and P. Williot 2 1 Department of Biology and Ecology of Fishes, Institute of Freshwater Ecology and Inland Fisheries, PO Box 850123, D-12561 Berlin, Germany. E-mail: fkirschb@igb-berlin.de 2 Cemagref, Continental Aquatic Resources Unit, 50 avenue de Verdun, F-33612 Cestas, France Received September 1999. Accepted June 2000. ABSTRACT The survival of the highly endangered Acipenser sturio L., 1758 depends nearly exclusively upon the establishment of captive broodstocks. Such measures were initiated in Germany in 1996, due to a transfer of 40 artificially reproduced individuals from France under a co-operation agree- ment. We report the results of rearing these fish for a period of 3 years under freshwater condi- tions. During the first year the fish being exclusively fed frozen chironomid larvae (N = 40) grew from a median of 27 cm (with range of 23-31 cm), averaging 71 g (42-112 g), to 43 cm (38-51 cm) and 280 g (168-505 g) at a mean temperature of 20 °C (13-27 °C). Following their transfer to larg- er tanks (approx. 5 m 3 ) at a mean temperature of 21 °C (17-24 °C), the fish (N = 27) reached a length of 68 cm (56-76 cm), averaging 1 281 g (512-2 097 g) at the end of the second year. Decreasing growth and increasing food conversion rates (FCR) during the first four months of the third year made us change the food composition (addition of large chironomids, krill and small marine fish). An increase in growth and a decrease in FCR was observed over the next four months resulting in a median length of 76 cm (58-89 cm), with a weight of 1 827 g (855-3 462 g) at the end of the third year (N = 27). Our fish showed rather large differences in growth, with some individuals reaching the maximum weight gain observed in wild fish, thus indicating the potential to optimise results by future testing involving additional natural food items in order to develop a formulated diet to stimulate early sexual maturation. Key words: Growth curve, recovery, broodstock, behaviour, sexual maturation, semiclosed sys- tem. RESUMEN Recuperación de Acipenser sturio L., 1758 en Alemania: características del crecimiento de los peces juveniles mantenidos en condiciones experimentales de interior La supervivencia del altamente amenazado Acipenser sturio L., 1758 depende casi exclusivamente del establecimiento de stocks de cría en cautividad. Tales medidas fueron iniciadas en Alemania en 1996, gra- cias a la transferencia desde Francia bajo un convenio de cooperación de 40 individuos reproducidos artifi- cialmente. Presentamos los resultados de la cría de estos peces por un periodo de tres años en condiciones dul- ceacuícolas. Durante el primer año los peces (N = 40) siendo alimentados exclusivamente con larvas congeladas de quironómidos crecieron desde una media de 27 cm (con rango de 23-31 cm), promediando 71 g (42-112 g), a 43 cm (38-51) y 280 g (168-505 g) a una temperatura media de 20 ºC (13-27 °C). A con- tinuación de su traslado a tanques más grandes (de aproximadamente 5 m 3 ) a una temperatura media de 21 ºC (17-24 ºC), los peces (N = 27) alcanzaron una longitud de 68 cm (56-76 cm), promediando 1 281 g (521-2 097 g) al final del segundo año. La disminución del crecimiento y el incremento de las tasas de con-