Determining the optimal time for artificial propagation in Hilsa shad (Tenualosa ilisha) based on thyroid and steroid hormones levels

Steroid hormones in teleost have an important role in gonadal development and sexual maturity. Hilsa shad (Tenualosa ilisha) 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±0.35 ppt, Temperature: 27±0.17 ºC, DO: 7.9±0.23 mg/L; Karoon river, Khorramshahr; 1st station), September-marine water (Salinity: 44.01±0.5 ppt, Temperature: 26.5±0.41 ºC, DO: 7.45±0.52 mg/L; Bahrakan Port, Persian Gulf; 2nd station), October-marine water (Salinity: 41.77±0.25 ppt, Temperature: 15.27±0.32 ºC, DO: 9.36±0.10 mg/L; Bahrakan Port, Persian Gulf; 3rd station), and November-marine water (Salinity: 40.01±0.28 ppt, Temperature: 14.91±0.37 ºC, DO: 9.45±0.18 mg/L; Bahrakan Port, Persian Gulf; 4th station). Blood samples were immediately collected by a 5 ml syringe from the caudal vein, and serum was separated after centrifuging (7640 g,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-β estradiol (E2), and testosterone (T). More samples at the 1st station were on the 5th gonadal development stage with the highest GSI index. The maximum and minimum serum E2 levels were recorded at the 1st and 2nd stations, respectively. The serum testosterone concentration at the 1st station was significantly higher than the other ones and the maximum T3 and T4 concentrations were recorded at the 4th station. The results of this study proposed that Hilsa shad females are ready for spawning in September and this time is proposed for collecting broodstocks from the Karoon river (Khorramshahr, Khuzestan) for artificial propagation.