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Simple Summary: The DKK gene family plays an important role in immune mechanisms and embryonic development, but studies on Pelodiscus sinensis have not been reported. In this study, for the first time in the context of P. sinensis, we analyzed the relevant features of the DKK gene family using bioinformatics methods and constructed transcriptional profiles and tissue expression profiles. The DKK1 and DKK3 genes were found to be highly expressed in the ovaries, while DKKL1 and DKK4 were significantly differentiated in the testes. In this study, we preliminarily investigated the function of the DKK gene family in the context of P. sinensis, and this study lays the foundation for further systematic research on the molecular mechanism of sex differentiation in P. sinensis. The DKK family is a canonical small family of WNT antagonists. Though recent studies have suggested that the DKK gene family may be involved in sex differentiation in Pelodiscus sinensis, there are still a lot of things about the DKK gene family that we do not know. In this study, we used bioinformatics methods to identify members of the DKK gene family in P. sinensis and analyzed their phylogeny, covariance, gene structure, structural domains, promoter conserved sites, signal peptides, gonadal transcription factors, transcriptional profiles, and tissue expression profiles. Additionally, qRT-PCR results were utilized for the validation and preliminary investigation of the function of the DKK gene family in P. sinensis. The results showed that the DKK gene family is divided into six subfamilies, distributed on six different chromosomal scaffolds containing different gene structures and conserved motifs with the same structural domains, and all of the members were secreted proteins. Our transcriptional profiling and embryonic expression analysis showed that DKKL1 and DKK4 were significantly expressed in the testes, whereas DKK1 and DKK3 were significantly upregulated in the ovaries. This suggests a potential function in sex differentiation in P. sinensis. Our results may provide a basic theoretical basis for the sex differentiation process in P. sinensis. [ABSTRACT FROM AUTHOR]

Simple Summary: The Asian yellow pond turtle (Mauremys mutica) is widely traded in China, and its artificial breeding has now become a major industry. However, the insufficient offspring supply and reproductive decline of farmed turtles make wild turtles more vulnerable. The present study was mainly designed to quantify the fecundity of M. mutica and attempt to screen for good reproductive performance in females. The parent–offspring relationships of all offspring in four consecutive years were confirmed using sixteen microsatellite loci. We also summarised the reproductive results of all females and counted the annual number of offspring and the variation in the number of offspring. The females were then divided into three types (stable, undulating and levelling off) according to the continuity. This study can provide the basis and materials for the creation of a good reproductive group and the study of the reproductive biology of turtles in M. mutica aquaculture. The Asian yellow pond turtle (Mauremys mutica) is widely traded in China, and its artificial breeding has now become a major industry. However, the insufficient offspring supply and reproductive decline of farmed turtles make the wild turtles more vulnerable. The present study was mainly designed to quantify the fecundity of M. mutica and attempt to screen for good reproductive performance in females. The genetic variability of the population and its genetic structure were also analysed. The parent–offspring relationships of all offspring in four consecutive years were confirmed using sixteen microsatellite loci. The genetic variability between the parents and offspring was low, and offspring of different years also showed little variability. We summarised the reproductive results of all females and counted the annual number of offspring and the variation in the number of offspring. The females were then divided into three types (stable, undulating and levelling off) according to the continuity. We selected seven females with good reproductive ability, which provided 16.94% of the annual contributions, while there were two females that had no offspring in four years. We also analysed the possible reasons for this difference and the importance of carrying out a family survey. This research can provide the basis and materials for the creation of a good reproductive group and the study of the reproductive biology of turtles in M. mutica aquaculture. [ABSTRACT FROM AUTHOR]

Simple Summary: In aquaculture, the survival and health of aquatic organisms are influenced greatly by external environmental factors. Photoperiod is one of the key environmental factors that affect the early growth, survival, metabolism, and immune system of crustaceans significantly. The aim of the present study was to investigate the impact of photoperiod on the growth, survival, enzyme activity, body color, and expression of growth-related genes in juvenile redclaw crayfish. Five photoperiod experimental groups were established (0L:24D, 6L:18D, 12L:12D, 18L:6D, and 24L:0D), each with three replicates, and reared for 30 days. The group with an 18L:6D photoperiod had higher juvenile crayfish survival rates, better growth performance, stronger antioxidant stress response, and immune defense capabilities. Additionally, artificial photoperiods altered the body color of the redclaw crayfish. The results of the present study lay a foundation for the elucidation of the mechanisms underlying photoperiod regulation of the physiological and biochemical responses of juvenile redclaw crayfish. Through a 30-day experiment, this study investigated the effects of five photoperiods (0L:24D, 6L:18D, 12L:12D, 18L:6D, and 24L:0D) on the survival, enzyme activity, body color, and growth-related gene expression of redclaw crayfish (Cherax quadricarinatus) juveniles. The results showed that C. quadricarinatus juveniles under 18L:6D and 24L:0D photoperiods exhibited the highest survival rate, which was significantly higher than the survival rates of juveniles under the other three photoperiods (p < 0.05). However, the 0L:24D group had the highest final body weight and weight gain rate, significantly surpassing those of the 12L:12D, 18L:6D, and 24L:0D groups (p < 0.05). Regarding enzyme activity and hormone levels, juveniles under the 18L:6D photoperiod exhibited relatively higher activity of superoxide dismutase (SOD), acid phosphatase (ACP), and lysozyme (LZM) enzymes than those under other photoperiods, but their levels of melatonin and cortisol were relatively low. In addition, the 24L:0D group showed the highest malondialdehyde (MDA) content. Analysis of gene expression levels revealed that retinoid X receptor (RXR) and α-amylase (α-AMY) genes in C. quadricarinatus juveniles exhibited significantly higher expression levels under the 18L:6D photoperiod than those under the other four photoperiods (p < 0.05). With increasing daylight exposure, the body color of C. quadricarinatus changed from pale blue to yellow–brown. In summary, C. quadricarinatus juveniles achieved high survival rates, good growth performance, strong antioxidant stress response, and immune defense capabilities under an 18 h photoperiod. Therefore, in the industrial seedling cultivation of redclaw crayfish, it is recommended to provide 18 h of daily light. Further, the study demonstrated the ability to manipulate the body color of C. quadricarinatus through controlled artificial photoperiods. These findings provide essential technical parameters needed for the industrial cultivation of C. quadricarinatus juveniles. [ABSTRACT FROM AUTHOR]

Male and female Chinese soft-shelled turtles (Pelodiscus sinensis) have sex-dimorphic growth patterns, and males have higher commercial value because of their larger size and thicker calipash. Thus, developing sex-specific markers is beneficial to studies on all-male breeding in P. sinensis. Here, we developed an accurate and efficient workflow for the screening of sex-specific sequences with ZW or XY sex determination systems. Based on this workflow, female and male P. sinensis reference genomes of 2.23 Gb and 2.26 Gb were obtained using de novo assembly. After aligning and filtering, 4.01 Mb female-specific sequences were finally identified. Subsequently, the seven developed sex-specific primer pairs were 100% accurate in preliminary, population, and embryonic validation. The presence and absence of bands for the primers of P44, P45, P66, P67, P68, and P69, as well as two and one bands for the PB1 primer, indicate that the embryos are genetically female and male, respectively. NR and functional annotations identified several sex-determining candidate genes and related pathways, including Ran, Eif4et, and Crkl genes, and the insulin signaling pathway and the cAMP signaling pathway, respectively. Collectively, our results reveal that a ZW-type sex-determination system is present in P. sinensis and provide novel insights for the screening of sex-specific markers, sex-control breeding, and the studies of the sex determination mechanism of P. sinensis. [ABSTRACT FROM AUTHOR]