Spawning induction and hormonal levels during final oocyte maturation in the silver perch (Bidyanus bidyanus) Berta Levavi-Sivan a, * , Rima Vaiman a , Ofer Sachs b , Itai Tzchori b a Department of Animal Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University, P.O. Box 12, Rehovot 76100, Israel b Aquaculture Research Station-DOR, M.P Hof Hacarmel 30820, Israel Received 18 November 2002; received in revised form 11 April 2003; accepted 15 April 2003 Abstract The silver perch (Bidyanus bidyanus Mitchell) (Teraponidae), is a native Australian freshwater fish that, due to its high potential for aquaculture, was introduced to Israeli fish farming. The objective of this study was to find an optimal method for inducing spawning of silver perch. The agents tested for this purpose were: human chorionic gonadotropin (hCG; 150 or 200 IU/kg BW); salmon gonadotropin releasing hormone analogue (sGnRHa at 10, 20, 30, or 40 Ag/kg BW); mammalian GnRH analogue (mGnRHa at 30 Ag/kg) and the combination of sGnRHa at 20 Ag/kg and domperidone at 5 mg/kg BW. Based on spawning success and relative fecundity, sGnRHa at the dose of 30 Ag/kg was found to be more efficient than hCG, mGnRHa or sGnRHa with domperidone. Since domperidone does not improve the GnRHa effect on final oocyte maturation (FOM) and spawning, it is suggested that the dopaminergic inhibition during the stages of FOM in the silver perch is weak. Therefore, the use of GnRHa alone is sufficient to induce spawning in this fish. Immunoreactive gonadotropin (IR-GtH) and estradiol levels increased after a single injection of sGnRHa, and peaked after 24 h. Plasma levels of 17a,20h-dihydroxy-4-pregnen-3-one (17,20-P) also increased significantly 24 h after the injection of mGnRHa, 12 h before spawning, suggesting that 17,20-P is the maturation-inducing steroid in silver perch. In order to reveal whether the heterologous gonadotropin may elicit an immunological reaction, silver perch was subjected to prolonged treatment with hCG. This treatment resulted in no detectable titer of antibodies against the mammalian gonadotropin. In conclusion, although hCG has no deleterious effects in this fish, and is the more commonly used for spawning induction, sGnRHa at 30 Ag/kg is the recommended 0044-8486/$ - see front matter D 2004 Elsevier Science B.V. All rights reserved. doi:10.1016/S0044-8486(03)00349-1 * Corresponding author. Tel.: +972-8-9489988; fax: +972-8-9465763. E-mail address: sivan@agri.huji.ac.il (B. Levavi-Sivan). www.elsevier.com/locate/aqua-online Aquaculture 229 (2004) 419 – 431