Endocrine disrupting chemicals (EDCs) including 17β-estradiol (E2) are widely distributed in the aquatic environment and are known to negatively affect the reproductive system of many animals, including fish. EDCs leading to feminization, altered sex ratio and reduced fecundity, it is possibly posing potential risks to the ecosystems. To investigate the potentially toxic effects of E2 exposure on little yellow croaker (Larimichthys polyactis, L. poliactis) who have a unique gonadal development pattern that males undergo a hermaphroditic stage. An experiment was set up where L. poliactis were maintained in tanks and exposed to E2 concentrations of 10 μg/L or no E2 exposure (the ethanol and control groups) from 30 to 90 days post-hatching (dph). After exposure, the E2 withdrawal and continual cultured to 150 and 365 dph. The morphological and histological analyses were used to compare the changes in the fish body and gonad under E2 exposure. The results showed that E2 exposure caused three major phenotypes at 30 and 60 days after treatment (dat), including ovary, ovotestis and gonadal development retardation compared with the control groups. The average ratio of these three phenotypes is 60.6%, 11.97% and 27.43%, respectively. The body length and weight of E2 exposure groups were repressed during the E2 exposure period, while it can recover after E2 withdrawal. However, the gonadal development (Gonadosomatic Index) of E2 exposure groups testis were retarded at 60 dat and doesn't recover until 365 dph. The sex determination/differentiation-related genes erα, erβI, erβII, fshβ and cyp11b2 were significantly decreased in E2-exposure male fish. This research highlights the E2 leads to feminization, disrupts testis maturation and spermatogenesis, this effect persisted into the stage of sexual maturity. Collectively, our findings provide insights into the molecular mechanisms underlying E2 disturbance of a marine economic fish reproduction.

Large yellow croaker (Larimichthys crocea), the most developing fish of China, suffering from both biotic and abiotic stressors. A genome-wide study was performed for the first time to investigate the roles of Toll-like receptor genes in large yellow croaker (LcTLRs) working in hypoxia response and Aeromonas hydrophila infection. 12 TLR genes were identified and annotated, and phylogenetic tree, analysis of structure and motifs demonstrated that TLRs were highly conserved. To further investigate the LcTLRs under environmental stress, expression pattern analysis of hypoxic response and Aeromonas hydrophila infection revealed that there were nine and six members of LcTLRs showing significant differential expression, indicating that they were concerned in hypoxia stress and disease responses. Meanwhile, their expression levels were validated utilizing qPCR. Taken together, a greater appreciation and understanding of TLRs function in the reaction to biotic and abiotic stress would ultimately lead to more efficiently environmental adaptation in large yellow croaker.

In this study, we compared the genetic diversity and structure of small yellow croaker (Larimichthys polyactis, LP), large yellow croaker (Larimichthys crocea, LC), and their reciprocal hybrids (LP ♀ × LC ♂ (LCP) and LC ♀ × LP ♂ (LPC)) using 14 microsatellite loci. Our results revealed that genetic diversity was highest in LCP, followed by LP and LPC, with LC exhibiting the lowest level. Additionally, among the two hybrid progenies, the number of loci in LCP deviating from Hardy–Weinberg equilibrium was lower. This suggests that LCP is a more appropriate choice as breeding material and has the potential to enhance germplasm resources. Based on the analysis of 14 microsatellite loci, we observed that both hybrid species clustered with their respective maternal parents. Specifically, LPC exhibited a closer genetic relationship to its maternal parent than LCP did. Furthermore, the majority of genes in LPC were inherited from its maternal parent (LP). In the LCP population, approximately 63% of individuals possessed gene profiles similar to those observed in LPC, while the remaining individuals displayed a mix from both parents. This study provides a strategic direction for the efficient utilization and management of novel germplasm resources in hybrid yellow croaker. Hybrid yellow croaker serves as an intermediate breeding material, playing a significant role in the genetic improvement of Larimichthys crocea and Larimichthys polyactis.