Effects of short periods of warm water fluctuations on reproductive endocrine axis of the pejerrey (Odontesthes bonariensis) spawning Mariano Elisio, Tomás Chalde, Leandro A. Miranda ⁎ Laboratorio de Ictiofisiología y Acuicultura, Instituto de Investigaciones Biotecnológicas-Instituto Tecnológico de Chascomús, (CONICET-UNSAM), Intendente Marino Km. 8,200 (B7130IWA), Chascomús, Buenos Aires, Argentina abstract article info Article history: Received 7 March 2012 Received in revised form 3 May 2012 Accepted 4 May 2012 Available online 11 May 2012 Keywords: Global warming Pejerrey Reproduction Sex hormones The aim of this study was to assess fluctuations in daily water temperature in Chascomús Lagoon during one year, and to evaluate whether the highest temperature recorded during pejerrey spawning season can pro- duce an endocrine disruption on brain–pituitary–gonads axis. Fish were subjected to daily temperature fluc- tuations: 17 °C to 19 °C (reproductive control), 19 °C to 25 °C, and 19 °C to 27 °C. After 8 days, ten fish per treatment were sacrificed and gene expression of gonadotropin-releasing hormone (GnRH-I, GnRH-II, GnRH-III), gonadotropin subunits-β (FSH-β, LH-β), glycoprotein hormone-α (GPH-α), gonadotropin recep- tors (FSH-R, LH-R), and gonadal aromatase (cyp19a1a) was analyzed. Also, plasma levels of sexual steroids and gonadal reproductive status were studied. Fish exposed to high temperature fluctuations quit spawning, presenting clear signs of gonadal regression. Fish recovered its spawning activity 11 weeks after heat treat- ment. At endocrine level, GnRH-I and FSH-β in both sexes, LH-β and GPH-α in males and FSH-R, LH-R and cyp19a1a in females decreased significantly in treated fish. Also, a strong reduction in plasma sex steroid levels was found for both sexes. This study demonstrated that pulses of warm water in natural environment during pejerrey spawning season can disrupt all levels of the reproductive axis, impairing reproduction. © 2012 Elsevier Inc. All rights reserved. 1. Introduction Over the past 100 years, the global average temperature of the Earth as well as the frequency of extreme asymmetric climatic events increased and it has been projected to rise at a rapid rate (IPCC, 2007; Brander, 2010). This phenomenon known as Global Warming, has led to an increase in temperature of several water bodies, affecting the quality of aquatic environment (Ficke et al., 2007). In this context, several studies have attempted to understand and predict the conse- quences of recent global warming on community structures of lake fish and the potential effects on the ecosystem function (Jeppesen et al., 2010). Nevertheless, studies of the possible consequences of global warming on fish reproduction in natural environments are still scarce (Pankhurst and King, 2010; Strüssmann et al., 2010). In teleosts, as in other vertebrates, the reproductive cycle is con- trolled by the brain–pituitary–gonadal axis. The pituitary gonadotropins (GtHs), namely follicle stimulating hormone (FSH) and luteinizing hor- mone (LH), play central roles in the regulation of gametogenesis and the production of sexual steroids (Zohar et al., 2010). Moreover, the regula- tion of gonadotropin secretion in fishes is a complex process, involving the reception of environmental cues, through brain pathways, mainly involving the gonadotropin-releasing hormone (GnRH) system and ste- roid feedback mechanisms (Popesku et al., 2008; Levavi-Sivan et al., 2010). It is well known that temperature is one of the main environ- mental factors influencing endocrine regulation of fish reproduction and that even small changes in this variable can cause alterations in the reproductive cycle (Pankhurst and King, 2010; Strüssmann et al., 2010). In this context, it has been demonstrated that high water tem- peratures affect brain–pituitary–gonad function, impairing gonadal de- velopment and reproduction of some fish species (Van der Kraak and Pankhurst, 1997; Tveiten et al., 2001; King et al., 2003, 2007; Okuzawa et al., 2003; Pankhurst and King, 2010; David and Degani, 2011; Hermelink et al., 2011; Levy et al., 2011). However, it has not been stud- ied if this variable can differentially affect all the levels of the reproduc- tive endocrine axis. The pejerrey (Odontesthes bonariensis Valenciennes 1835) is a rep- resentative fish from lagoons of the Pampas region of Argentina. The high quality of its flesh and its attractiveness as a game fish make it a good candidate for aquaculture (Gómez et al., 2007; Somoza et al., 2008). This species is a multiple spawner fish with a marked seasonal reproductive cycle, possessing a major spawning period during spring and a smaller one in autumn, alternated with periods of reproductive inactivity in summer and winter (Calvo and Morriconi, 1972; Strüssmann, 1989; Miranda et al., 2006). It has been reported that pejerrey spawning season starts at the end of winter, beginning of spring, when the photoperiod increases and water temperatures reach approximately 13 °C to 15 °C (Strüssmann, 1989; Miranda et Comparative Biochemistry and Physiology, Part A 163 (2012) 47–55 ⁎ Corresponding author. Tel.: + 54 2241 430323; fax: + 54 2241 424048. E-mail address: lmiranda@intech.gov.ar (L.A. Miranda). 1095-6433/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.cbpa.2012.05.178 Contents lists available at SciVerse ScienceDirect Comparative Biochemistry and Physiology, Part A journal homepage: www.elsevier.com/locate/cbpa