Spawning of Siberian sturgeon A. baerii was induced hormonally using mammalian gonadotropin-releasing hormone analogue GnRHa ([D-Ala(6), Des Gly(10)]-LHRH Ethylamide) in Uruguay (35 degrees S) and results were compared with treatments made in France (45 degrees N). Testosterone, estradiol-17 beta and 17, 20 beta-dihydroxy-4-pregnen-3-one (17, 20 beta P) blood plasma concentrations were measured by RIA before and after GnRHa treatment. Females (6 years old) injected in Uruguay with a single dosis of 10 mu g kg(-1) of GnRHa ovulated spontaneously between 25 and 39 h post-treatment, while males (6 years old) released sperm after 26 h of stimulation. Hormonal induction was made at 18-19 degrees C. Eggs and larvae of medium quality were obtained. In France, females (10 years old) induced with two doses of 5 mu g kg(-1) b.w. of GnRHa (similar to 15 degrees C) did not finish their follicle maturation, while males (16 years old) released up to 100 ml of good quality sperm after a single injection with 5 mu g kg(-1) b.w. of GnRHa. The 17, 20 beta P levels showed a co-evolution with the sperm volume released by 16 years old males suggesting that this could be the maturing inducing steroid (MIS) for A. baerii males. The 17, 20 beta P levels were undetectable before GnRHa treatment and showed an increase in two females with maturing follicles, but more studies must be done in order to conclude about the physiological role of this hormone as MIS in female A. baerii. To our knowledge this is the first time that spawning induction and egg and larvae of Siberian sturgeon were obtained in a southern hemisphere country, with a warmer climate than in the north while also being exposed to a shift in seasonal temperature and light cycle.