As global aquaculture continues to expand, increasing efforts are focusing on assisted reproductive technologies. This study sought to test whether salmon GnRH [D-Arg6, Pro9NEt]) analogue (sGnRHa) + domperidone injection at 0.25 mL/body weight (BW; 5-μg sGnRHa + 2.5-mg domperidone), 0.5 mL/kg BW (10-μg sGnRHa + 5-mg domperidone), or 1.0 mL/kg BW (20-μg sGnRHa + 10-mg domperidone) affects spawning performance and gamete quality in wild-caught Levantine scraper, Capoeta damascina. The ability of these treatments to elicit a response was further examined by in vivo stimulation of estradiol (E2) and 17α,20β-dihydroxy-4- pregnen-3-one (DHP) and by its in vivo potency to induce oocyte maturation (OM). Females that received saline injection (control) did not spawn, whereas sGnRHa + domperidone induced ovulation and spawning across the hormonal gradient. Spawning success was highest with the 0.5 mL/kg dosage (80%) and female latency period decreased with increasing dosage. Females treated with 0.5 mL/kg had a significantly higher fecundity than those injected with 0.25 or 1.0 mL/kg. Mean oocyte diameter significantly increased in females treated with 0.5 or 1.0 mL/kg. Fertilization success, hatching rate, larvae morphology, and survival were not affected by hormonal treatment. At 12 h postinjection, E2 levels significantly declined in females treated with 0.5 or 1.0 mL/kg, whereas DHP levels significantly increased across the hormonal gradient. This steroidogenic shift is supported by histological analyses, where OM was accelerated by administration of sGnRHa + domperidone in a dose-dependent manner. In conclusion, the 0.5 mL/kg dosage of sGnRHa + domperidone is recommended for assisted reproduction of Levantine scraper.
