Background/Objectives: The Chinese soft-shelled turtle (Pelodiscus sinensis) is an important species in freshwater aquaculture. Genetic admixture and degradation due to rapid industry expansion threaten sustainable development. This study aims to assess the genetic diversity and structure of six P. sinensis populations for better management. Methods: We combined morphological analysis and microsatellite markers to evaluate the genetic diversity of six populations. A discriminant function based on morphology was developed, achieving 71.4% classification accuracy. Two SSR markers were identified to specifically distinguish the HS population. Results: The six populations were classified into three subgroups. Frequent gene flow was observed among the CY, W, and DT populations, with most genetic variation occurring within individuals. However, significant genetic differentiation was detected between populations. While gene flow enhanced diversity, it suppressed differentiation. Conclusions: This study provides insights into the genetic structure and diversity of six P. sinensis populations. The discriminant function and SSR markers offer a basis for germplasm conservation and management, supporting sustainable aquaculture development.

This study was conducted to investigate the effects of replacing fish meal with either whole-fat or defatted krill powder on the growth, body color, immunity, and related gene expression of red–white koi carp. A total of 630 red–white koi carp with an initial body mass of 13.5 ± 0.05 g were randomly divided into seven groups with three replicates per group and 30 fish per replicate. The control group was fed a basic diet (C0). The other six diets were supplemented with different levels of whole krill meal or defatted krill meal as replacements (10% whole fat, 20% whole fat, 30% whole fat, 10% defatted, 20% defatted, and 30% defatted) in the experimental groups, named W10, W20, W30, D10, D20, and D30, respectively, for a total duration of 60 days. The growth, body color, immunity and gene expression indexes were measured in the koi after completion. The results indicate the following. (1) Compared with C0, the experimental groups of koi showed a significant increase in the specific growth rate (SGR) (p < 0.05), while the hepatosomatic index (HSI) and viscerosomatic ratio (VSI) decreased. Additionally, there was a significant increase in the relative expression level of insulin-like growth factor (IGF-1) in both the liver and muscle (p < 0.05). (2) The experimental groups of koi carp exhibited a significant increase in the carotenoid content in the scales and skin, as well as an elevated relative expression level of the tyrosinase (TYR) gene in the muscle (p < 0.05). (3) The lysozyme (LZM) and superoxide dismutase (SOD) activities were significantly increased in the experimental groups compared to C0 (p < 0.05). Additionally, the SOD activity was significantly higher in the defatted groups than in the whole-fat groups (p < 0.05). Furthermore, the liver alkaline phosphatase (AKP) activity was significantly lower in the D20 and D30 groups compared to the other five groups. (4) The expression level of LPL was significantly lower in the liver and muscle of the whole-fat group compared to the defatted group (p < 0.05). Tissue section observation revealed that the hepatocytes in the W20 and W30 groups exhibited a reduced size and an increased lipid droplet count, while the vacuolar degeneration of the hepatocytes increased in the D30 group. In conclusion, replacing fish meal with whole-fat or defatted krill powder or defatted Antarctic krill meal significantly improves the growth performance, body color, and immunity of red–white koi carp. However, excessive addition of krill meal can easily cause liver damage. The recommended replacement level for whole krill powder is 20% to 30%, while defatted krill powder should be replaced at a level of 10% to 20%.

Hybridization is an effective method for the genetic improvement of breeding varieties, while establishing standardized management systems and identification methods is an important foundation for obtaining stable hybrid new varieties with desirable traits. This study conducted measurements and analyses of eight morphological indicators of three Chinese soft‐shelled turtle ( Pelodiscus sinensis ) populations: the Huangsha turtle ( P. sinensis Huangsha, HS), Japanese turtle ( P . sinensis Japanese strains, JP), and their hybrid F1 generation (HS ♂ × JP ♀, HJ). Based on several important indicators, a discriminant function was established, and after cross‐validation, the comprehensive discriminant accuracy was 86.4%. In addition, we used super‐genotyping‐by‐sequencing (GBS) sequencing technology to analyze the genetic structure and genetic diversity of the three populations. The results showed that the HJ population had a closer genetic relationship with the JP population as the maternal parent and a farther genetic relationship with the HS population. The genetic diversity was between the HS and JP populations, and the genetic distance between the HS and JP populations was far. Through fingerprint analysis technology, core SNP markers for germplasm identification were screened, and a total of 148 core SNP marker loci were obtained. One SNP marker that could distinguish the HJ population from the HS population was developed. This study will provide reference for the hybrid breeding and genetic management of Chinese soft‐shelled turtle.

The conjugation states of bile acids (BAs) have been demonstrated to affect BAs regulatory functions. This study aimed to investigate the effects of conjugated or non‐conjugated BA additions on growth performance, liver health, and BA metabolism in pearl gentian grouper ( Epinephelus lanceolatus ♂ × E. fuscoguttatus ♀), as well as to elucidate the underlying mechanisms. The 300 healthy experimental fish, each with an average initial body weight (IBW) of 15.21 ± 0.04 g, were randomly distributed into 12 tanks (300 L per tank). The experiment consisted of four dietary groups, with three replicates per group: the control diet (CD) group, the plant protein‐based diet (PD) group, the PD supplemented with conjugated BAs (CBD) group, and the PD supplemented with non‐conjugated BA diet (NBD) group. The findings indicated that, in comparison to the CD group, the grouper fed a PD exhibited deleterious effects on growth performance, BA metabolism, and liver health. This was evidenced by increased levels of of oxidative stress, endoplasmic reticulum (ER) stress, apoptosis, and inflammatory response. In comparison to the PD group, the CBD treatment demonstrated favorable outcomes with respect to growth performance and liver health in the grouper. Additionally, it facilitated BA metabolism, as evidenced by enhanced BA transport, reabsorption, and recycling. Compared to PD group, the NBD treatment further impaired BA metabolism and induced cell apoptosis. Additionally, six metabolites, 3‐Dehydrocarnitine, Stizolobate, Bilastine, S‐(‐)‐Ureidoglycolate, 5,6‐Dihydroxyindole, and 4‐O‐methylnorbelladine‐, were identified as biomarkers among the treatment groups. Moreover, high plant‐protein replacement and BAs addition both impacted the pathways associated with the “Biosynthesis of various plant secondary metabolites“ and “Central carbon metabolism in cancer. “In conclusion, the conjugated BAs improve growth performance, liver health, and BA metabolism in pearl gentian grouper fed a high plant‐protein diet.