Optimization of a protocol for fertilized egg production in Japanese eel using recombinant gonadotropins, LHRHa, pimozide, and 17α-hydroxyprogesterone

Abstract

Recently, two types of Japanese eel recombinant gonadotropins (rGths), recombinant follicle-stimulating hormone (rFsh) and luteinizing hormone (rLh), have been successfully produced. However, the protocol for obtaining fertilized eggs using rGths has not yet been optimized. In this study, to establish a new protocol for obtaining fertilized eggs from Japanese eel, we decided to use rFsh as an inducer of vitellogenesis and focused on optimizing the final oocyte maturation (FOM) and ovulation induction method using rLh, 17α-hydroxyprogesterone (OHP), Lh-releasing hormone analog (LHRHa), and pimozide. Our findings indicates that OHP injection is crucial for stable ovulation induction. Quality evaluations revealed that the FOM and ovulation induction methods using LHRHa, pimozide, and OHP significantly improved the egg quality (fertility, hatchability, and larval survival) better than the methods using rLh and OHP (P < 0.05). Furthermore, effects of different doses of LHRHa and pimozide on egg quality were examined. We found that 0.5 mg/kg BW LHRHa, 10 mg/kg BW pimozide, and 2.0 mg/kg BW OHP injections was an effective and economical induction method, and this method was defined as the rGths method. When comparing the quality and quantity of eggs and larvae obtained by the rGths method with those obtained by the conventional method, the former displayed superior quality. In addition, the number of eggs, fertilized eggs, and normal larvae at 6 days post hatch was significantly higher in broodstock matured by the rGths method compared to the conventional method (P < 0.05). These results suggest that the new rGths method is a promising alternative for the artificial sexual maturation Japanese eel, potentially leading to a higher yield of larvae.