To assess the optimal dietary protein requirement of adult red swamp crayfish (Procambarus clarkii) farming in the rice field, six isoenergetic and isolipid diets were formulated to contain graded levels of 28%, 31%, 34%, 37%, 40% and 43% crude protein (called Diet 28–43 group). Each diet was assigned to a triplicate of 20 experimental crayfish with the average initial body weight of (15.17 ± 0.23) g for 42 days. Our results showed that the final body weight, weight gain rate and specific growth rate of red swamp crayfish adult in the Diet 34, Diet 37, Diet 40 and Diet 43 groups were significantly higher than those of other groups (P < 0.05), but no significant difference was found in meat yield, hepatosomatic index and survival rate among all groups. The highest crude protein content of muscle was found in crayfish fed the diet containing 37% protein (P < 0.05). Hemolymph total protein, globulin and total bilirubin concentration showed a positive correlation with dietary protein level, but alanine transaminase activity was negatively correlated with dietary protein level (P < 0.05). Different dietary protein level had no significant effect on the aspartate transaminase activity of crayfish (P > 0.05). Activities of trypsin and lipase in the intestine were significantly affected by dietary protein levels (P < 0.05), while amylase activity showed no significant difference (P > 0.05). Moreover, higher dietary protein significantly increased the antioxidant and non-specific immunity enzyme activity. Broken-line regression analysis based on weight gain rate and specific growth rate showed that the optimal dietary protein level for maximum growth performance of crayfish was 32.68%. According to the present study on the growth performance, the muscle of Diet 28 group (SM) and Diet 34 group (LM) individuals were selected for transcriptome sequencing. The results showed that there were 444 differential genes in SM and LM, of which 282 genes were up-regulated and 162 genes were down-regulated. DEGs of SM and LM groups differential genes were mainly enriched in citrate cycle, pyruvate cycle, glycolysis/gluconeogenesis, etc. Beyond that, transcriptomic results also hinted that glycolysis/gluconeogenesis and citrate cycle signaling pathways might be its growth change mechanisms. In addition, the aldo, eno, pk, pdhb, adh, sdha, fh, mdh2, cs were also identified as the key factors involved in glycolysis/gluconeogenesis and citrate cycle pathways. In conclusion, combining growth performance and transcriptome data, we recommended that diets with 32.68%− 34.00% protein were optimal for red swamp crayfish in the rice-shrimp farming pattern.

Cipangopaludina chinensis, as a financially significant species in China, represents a gastropod in nature which frequently encounters starvation stress owing to its limited prey options. However, the underlying response mechanisms to combat starvation have not been investigated in depth. We collected C. chinensis under several times of starvation stress (0, 7, 30, and 60 days) for nutrient, biochemical characteristics and transcriptome analyses. The results showed that prolonged starvation stress (> 30 days) caused obvious fluctuations in the nutrient composition of snails, with dramatic reductions in body weight, survival and digestive enzyme activity (amylase, protease, and lipase), and markedly enhanced the antioxidant enzyme activities of the snails. Comparative transcriptome analyses revealed 3538 differentially expressed genes (DEGs), which were significantly associated with specific starvation stress-responsive pathways, including oxidative phosphorylation and alanine, aspartate, and glutamate metabolism. Then, we identified 40 candidate genes (e.g., HACD2, Cp1, CYP1A2, and GPX1) response to starvation stress through STEM and WGCNA analyses. RT-qPCR verified the accuracy and reliability of the high-throughput sequencing results. This study provides insights into snail overwintering survival and the potential regulatory mechanisms of snail adaptation to starvation stress.

The rice flower carp ( Cyprinus carpio ) is an important fish in integrated rice-fishery farming. Here, we performed the first genome-wide association study (GWAS) for seven growth traits (including body mass, total length, body length, body height, body width, caudal-peduncle depth, and eye spacing) in 200 rice flower carp samples using 369,688 high-quality SNPs and 42,225 indels obtained by double-digest genotyping-by-sequencing (ddGBS). The morphometrics of these traits were highly correlated (Pearson’s correlation coefficients = 0.74–0.99, p < 0.001). GWAS detected 15, 5, 4, 26, 7, 16, and 17 loci significant associated (-log10P ≥ 5) with body mass, total length, body length, body width, body height, caudal-peduncle depth, and eye spacing, respectively. Subsequently, within the 50 kb upstream and downstream regions surrounding these significant loci, 38, 19, 18, 20, 52, 27, and 37 candidate genes for the seven growth traits were detected, respectively. Importantly, B6_4352672 and A8_4978825 were significantly associated with more than five growth traits. These results showed loci significantly associated with more than five growth traits will be helpful for future marker-assisted selection (MAS). Interestingly, chromosomes A8 and B25 had many loci significantly associated with growth traits, most of which were shared among multiple growth-related traits. These results indicated that chromosome A8 and B25 may be closely related to growth traits. Our findings not only help understand the genetic architecture of growth traits in fish but facilitate the identification of candidate genes for marker-assisted selection towards breeding faster-growing rice flower carp in the future.

An ecotoxicological feasibility study was conducted to investigate the effects of ammonia-N(NH4Cl)(0 mg/L 、50 mg/L、150 mg/L、250 mg/L) stress on the activities of GST in livers of wild four-naris carp population and farmed four-naris carp population to ammonia-N exposure in fresh water for 15 days.The results showed that:under the same ammonia concentrations and the same stress time,the change trends of activity of GST enzyme of the wild four-naris carp population was similar to the farm four-naris carp population.The activity of GST enzymes of the wild population was higher than the farm population markedly,except for 250 mg/L groups in the 5 d and 10 d.Under the high concentration stress of ammonia,the GST activity in the livers of the wild population reached the top level faster than the farm population,it suggested that the wild four-naris carp population has a stronger resistance to ammonia stress.