en Biology & physiology Biology & physiology پژوهشي Orginal research papers <span style="font-size:12pt"><span new="" roman="" style="font-family:" times=""><span style="font-size:11.5pt"><span style="color:black">Steroid hormones in teleost have an important role in gonadal development and sexual maturity. Hilsa shad (<i>Tenualosa ilisha</i>) is important for fisheries in the South of Iran. Any information on steroid hormones of Hilsa shad brooders and their relationship with the spawning period provides a vital step for studies on the propagation and culture of this species. Fish samples were captured from four location-time stations: September-fresh water (Salinity: 5.2&plusmn;0.35 ppt, Temperature: 27&plusmn;0.17 &ordm;C, DO: 7.9&plusmn;0.23 mg/L; Karoon river, Khorramshahr; 1^st station), September-marine water (Salinity: 44.01&plusmn;0.5 ppt, Temperature: 26.5&plusmn;0.41 &ordm;C, DO: 7.45&plusmn;0.52 mg/L; Bahrakan Port, Persian Gulf; 2^nd station), October-marine water (Salinity: 41.77&plusmn;0.25 ppt, Temperature: 15.27&plusmn;0.32 &ordm;C, DO: 9.36&plusmn;0.10 mg/L; Bahrakan Port, Persian Gulf; 3^rd station), and November-marine water (Salinity: 40.01&plusmn;0.28 ppt, Temperature: 14.91&plusmn;0.37 &ordm;C, DO: 9.45&plusmn;0.18 mg/L; Bahrakan Port, Persian Gulf; 4^th station). Blood samples were immediately collected by a 5 ml syringe from the caudal vein, and serum was separated after centrifuging (7640 <i>g</i>,10 min). Also, gonad developmental stages and Gastro-somatic index (GSI) were determined after necropsy of euthanized fish. The enzymatic Immunological Assay method is used for hormone measurements, including thyroxin (T4), triiodothyronine (T3), 17-&beta; estradiol (E2), and testosterone (T). More samples at the 1^st station were on the 5^th gonadal development stage with the highest GSI index. The maximum and minimum serum E2 levels were recorded at the 1^st and 2^nd stations, respectively. The serum testosterone concentration at the 1^st station was significantly higher than the other ones and the maximum T3 and T4 concentrations were recorded at the 4^th station. The results of this study proposed that Hilsa shad females&nbsp;are ready for spawning in September and this time is proposed for collecting broodstocks from the Karoon river (Khorramshahr, Khuzestan) for artificial propagation.</span></span></span></span> Persian Gulf, Karoon River, Thyroxin, Triiodothyronine, 17-β estradiol, Testosterone, Tenualosa ilisha 741 757 http://jifro.ir/browse.php?a_code=A-10-3211-1&slc_lang=en&sid=1 A. Asadi Eidivand asadasadi64@gmail.com 100319475328460046382 100319475328460046382 No Department of Fisheries, Faculty of Marine Natural Resources, Khorramshahr University of Marine Science and Technology, Khorramshahr, Iran S.M. Mousavi seied1356@yahoo.com 100319475328460046383 100319475328460046383 Yes Department of Fisheries, Faculty of Marine Natural Resources, Khorramshahr University of Marine Science and Technology, Khorramshahr, Iran S.R. Fatemi Tabatabei fatemi_r@scu.ac.ir 100319475328460046384 100319475328460046384 No Department of Basic Science, Faculty of veterinary Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran M. Zakeri mhdzakeri@yahoo.com 100319475328460046385 100319475328460046385 No Department of Fisheries, Faculty of Marine Natural Resources, Khorramshahr University of Marine Science and Technology, Khorramshahr, Iran N. Zanguee zanguee_n@yahoo.com 100319475328460046386 100319475328460046386 No Department of Fisheries, Faculty of Marine Natural Resources, Khorramshahr University of Marine Science and Technology, Khorramshahr, Iran