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Simple Summary: The small yellow croaker, a fish of high economic value in East Asia, faces population decline due to overfishing and environmental issues. The development of effective breeding programs for this species is crucial, and accurate parentage assignment is essential for such programs. This study developed a microsatellite marker-based multiplex PCR system for precise parentage identification in the small yellow croaker. The researchers utilized the assembled reference genome to select highly polymorphic markers and optimized a multiplex PCR system for simultaneous amplification. The system was validated using controlled mating pairs and successfully applied to a group mating scenario, demonstrating high accuracy in assigning offspring to their parents. This system offers a valuable tool for pedigree management, selective breeding, and conservation efforts for the small yellow croaker, facilitating sustainable aquaculture practices and genetic improvement. (1) Background: The small yellow croaker, an economically important fish in East Asia, has been subjected to population declines due to overfishing and environmental pressures. The development of effective breeding programs is considered crucial for the species, and accurate parentage assignment is deemed essential for such programs. (2) Methods: The assembled reference genome of the small yellow croaker was utilized to select highly polymorphic microsatellite markers. A multiplex PCR system was optimized for the simultaneous amplification of these markers. The system's accuracy was validated using controlled mating pairs and subsequently applied to a group mating scenario. (3) Results: The developed multiplex PCR system demonstrated high accuracy in assigning offspring to their parents in both the controlled and group mating scenarios. (4) Conclusions: The system is presented as a valuable tool for pedigree management, selective breeding, and conservation efforts for the small yellow croaker, facilitating sustainable aquaculture practices and genetic improvement. [ABSTRACT FROM AUTHOR]

We investigated the effects of fadrozol, an aromatase inhibitor (AI), and 17α-methyltestosterone (MT) on the induction of sex change in juvenile longtooth grouper Epinephelus bruneus, via histological observation of gonads. Changes in the mRNA expression of GtH subunits (FSH-β and LH-β) in the pituitary, and estradiol-17β (E2) and 11-ketotestosterone (11-KT) levels in the blood were also surveyed after AI and MT treatment. Juvenile longtooth groupers (113±17 g body weight; 16.2±1.2 cm body length) received intramuscular injections of AI at 3 (3-AI) and 5 (5-AI) mg/kg BW doses and MT at a 5 mg/kg BW (5-MT) dose. At week 7 post-injection, 3-AI and 5-MT oocytes were degenerated, and gonads of the 5-AI group initiated spermatogenesis. At week 21 post-injection, 3-AI- and 5-MT-treated gonads contained spermatogonia and spermatocytes, while 5-AI treatment induced advanced stages of spermatogenesis. The serum E2 level showed no significant differences throughout the experimental period, whereas that of 11-KT was significantly elevated in the 5-AI group at weeks 7 and 21 post-injection. A significant increase in the expression of FSH-β mRNA was evident in the 5-AI group at week 21 post-injection. In contrast, LH-β mRNA expression did not significantly differ among groups during the experimental period. These results imply that sex change has two stages in the longtooth grouper. In the first stage, oocytes are degenerated by the stimulation by 11-KT, and in the second stage spermatogenesis occurs, owing to the co-effects of 11-KT and FSH-β. [ABSTRACT FROM AUTHOR]