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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]

Simple Summary: We explored the effect of maternal size on offspring size and number using a 4-year dataset based on paternity analyses in Asian yellow pond turtle, Mauremys mutica, and found that the maternal size significantly affected the offspring number but not offspring size. The offspring size was significantly correlated with maternal age. Our results suggest that the offspring size-number trade-off theory does not apply to cultured M. mutica and also provides basic data for the efficient artificial breeding management of M. mutica in captivity. Offspring size-number trade-off is a critical component of life-history theory and is important for further understanding the reproductive strategies of animals. The relationship between this trade-off and maternal size has been explored in several turtle species, except for the Asian yellow pond turtle, Mauremys mutica. To investigate how the maternal condition affects offspring size and number, we explored the relationships among the maternal body size and the number and size of cultured M. mutica hatchlings using a 4-year dataset. Our results showed that different females not only produced different sizes of offspring but also produced different numbers of offspring. No trade-off in egg size number was detected. According to regression analysis, we did not find that the maternal body size significantly influenced the offspring mass; however, we detected that the offspring size was significantly correlated with the clutch size and maternal age. The mean body mass of offspring increased with maternal age, and the clutch size varied significantly over four years, which was correlated with offspring size, maternal body size and age. However, the number of offspring per female increased with the maternal plastron length rather than age. Our results were inconsistent with the optimal offspring size theory in that females did not increase their offspring size but rather increased the offspring number to increase their fitness, which will also provide a basis for the efficient cultivation management of turtles. [ABSTRACT FROM AUTHOR]

Simple Summary: Pelochelys cantorii is critically endangered and rarely seen in the wild, and only 13 adults are being kept in captivity in China. For the purpose of reinforcing the conservation and management of P. cantorii, the Pearl River Fisheries Research Institute (Chinese Fishery Academy of Sciences) successfully bred more than 800 turtles from 2015 to 2020. In this study, we developed and characterized 10 simple sequence repeat markers from the RNA transcriptome of P. cantorii, established two multiplex PCR systems, and obtained the genetic structure and genetic diversity of the artificially conserved population. The aim was to obtain viable second-generation P. cantorii with the highest genetic diversity to implement population recovery plans for this species. To understand the genetic structure of the protected turtle species Pelochelys cantorii we used transcriptome data to design more than 30,000 tri- and tetranucleotide repeat microsatellite primer pairs, of which 230 pairs were used for laboratory experiments. After two screenings, only 10 microsatellite markers with good specificity, high amplification efficiency, and polymorphisms were obtained. Using the selected primers, two multiplex PCR systems were established to compare and analyze the genetic diversity of artificially assisted breeding generations from four parents (two females and two males) continuously bred over two years. A total of 25 alleles were detected among the 10 microsatellite loci of the offspring. The polymorphism information content (PIC) was 0.313–0.674, with an average of 0.401, among which two loci were highly polymorphic (PIC ≥ 0.5). The number of alleles was 2–5 and the number of effective alleles was 1.635–3.614. The observed heterozygosity was 0.341–0.813, with an average of 0.582, whereas the average expected heterozygosity was 0.389–0.725, with an average of 0.493. Moreover, on the basis of Nei's genetic distance and the Bayesian clustering algorithm, the 182 offspring were divided into two subgroups, and the results corresponded to the two maternal lines. This is the first study to investigate the molecular markers of P. cantorii, and the results obtained can be used to protect genetic resources and provide a genetic basis for the design of population recovery plans. [ABSTRACT FROM AUTHOR]

Simple Summary: Spermatogenesis in Pelodiscus sinensis has distinct seasonal characteristics. Spats1 acts a key function in germ cell differentiation in mammals, yet its study in P. sinensis has not been reported. Here, we cloned the coding sequences (CDS) of Spats1 for the first time and characterized its expression in different tissues. In addition, the expression characteristics of Spats1 in the testis during different seasons and the expression pattern in embryos and adults after steroid hormone treatment were also investigated. The present research provides a preliminary study on the physiological regulation of Spats1 in P. sinensis, and lays the foundation for further systematic investigation of the molecular mechanisms of spermatogenesis and release in P. sinensis. Spats1 (spermatogenesis-associated, serinerich 1) has been characterized as a male-biased gene which acts an important role in the germ cell differentiation of mammals. Nevertheless, the function of Spats1 in the Chinese soft-shelled turtle (P. sinensis) has not yet been reported. To initially explore the expression of Spats1 in P. sinensis and its response to sex steroid treatment, we cloned the CDS of Spats1 for the first time and analyzed its expression profile in different tissues, including the testes in different seasons. The Spats1 cDNA fragment is 1201 base pairs (bp) in length and contains an open reading frame (ORF) of 849 bp, which codes for 283 amino acids. Spats1 mRNA was highly expressed in the testes (p < 0.01) and barely detectable in other tissues. In P. sinensis, the relative expression of Spats1 also responsive to seasonal changes in testis development. In summer (July) and autumn (October), Spats1 gene expression was significantly higher in the testes than in other seasons (p < 0.05). Spats1 mRNA was found to be specifically expressed in germ cells by chemical in situ hybridization (CISH), and it was mainly located in primary spermatocytes (Sc1), secondary spermatocytes (Sc2) and spermatozoa (St). Spats1 expression in embryos was not significantly changed after 17α-methyltestosterone (MT)and 17β-estradiol (E2) treatment. In adults, MT significantly induced Spats1 expression in male P. sinensis. However, the expression of Spats1 in testes was not responsive to E2 treatment. In addition, the expression of Spats1 in females was not affected by either MT or E2 treatment. These results imply that Spats1 is a male-specific expressed gene that is mainly regulated by MT and is closely linked to spermatogenesis and release in P. sinensis. [ABSTRACT FROM AUTHOR]