Starvation is a major environmental stress, which has a broad effect on the physiology and ecology of aquatic animals. In this study, Monopterus albus was starved for 30 days at (20 +/- 0.5) degrees C, and the activities of protease, trypsin, amylase and lipase in its digestive organs were measured on the 0, 3rd, 5th, 10th, 15th, 20th, and 30th day of starvation. The results showed that starvation had definite effects on the activities of all test enzymes. With the prolongation of starvation, the activities of test enzymes decreased, which was most significant when the fish was starved for 5-10 days. After 10 days of starvation, the decreasing trend of the enzyme activities became less obvious.
The use of artificial substrates and biofloc technology can favor fish culture and improve water quality. The aim of this study was to evaluate whether artificial substrates and carbon source additions modify the microbial activity of water bodies. The diversity and structure of microflora in the water after adding artificial substrates and carbon sources to the ponds were analyzed using high-throughput sequencing based on the V3-V4 region of 16S rRNA genes. The results showed that there was no difference in the richness and diversity of intestinal microflora between the control and experimental groups. Principal coordinate analysis (PCoA) and nonmetric multidimensional scaling (NMDS) showed that artificial substrate and carbon source addition changed the structure of the microflora. The results of a linear discriminant analysis (LDA) effect size (LefSe) indicated 11 biomarkers in the EGˍst group. Spearman correlation heatmap analysis showed that environmental factors affected the bacterial communities, and the results of a redundancy analysis indicated that chemical oxygen demand was a critical factor in controlling the bacterial communities in the water. These results provide an understanding of the effect of artificial substrate and carbon source addition on bacterial diversity and community composition in water.
The experiment was carried out to investigate the effects of intermittent food-deprivation on growth,digestive enzyme activities and some serum biochemical indices in the rice-field eel,Monopterus albus.A 64-day growth trial with five feeding regimes was conducted using the live tubificid worms(Limnodrilus hoffmeisteri)as the food at(25±1)℃.Groups of fish were deprived of food for 1,2,4,8 day(s)and then followed by satiation re-feeding for the corresponding day(s),respectively(i.e.S1F1,S2F2,S4F4 and S8F8 groups).The fish fed to satiation daily throughout the experiment served as the control group(i.e.C).The results showed that,deprived fish had significantly lower specific growth rates(SGR),relative weight gains and final body weights,but significantly higher actual feeding rates,than that of the control fish(P0.05).Moreover,the fish in S1F1 group had significantly higher feed conversion efficiency(FCE)than those of any other groups(P0.05).It indicated that the partial growth compensation was elicited by various extents of intermittent food-deprivation,and that the fish of S1F1 group showed the best growth compensation.The protease activity of stomach in the S1F1 group was significantly higher than that in the S2F2 group(P0.05),and the protease activities of stomach in both of the two groups were significantly higher than those in other groups(P0.05).There was no difference in amylase activities of liver,stomach,foregut and hindgut among fish in all groups(P0.05).In the liver and hindgut,the S1F1 group had significantly higher lipase activities than other groups of the control,the S4F4 or the S8F8(P0.05).In all groups of the deprived fish,the serum total protein contents and glucose contents were slightly higher and lower than that in the control group,respectively,however,there was no significant difference among the five treatments(P0.05).There was no significant difference in serum total cholesterol level between the control group and S1F1 group(P0.05),and the serum total cholesterol levels in these two groups were significantly higher than that of any other group(P0.05).In contrast,among the groups of S2F2,S4F4 or S8F8,the serum total cholesterol level gradually descended with the more serious intermittent food-deprivation.These results suggested that the growth compensation in the rice-field eel could be achieved partially through the enhancement of the activities of some of digestive enzymes,food utilization efficiency,and the physiological adaptability of digestion,and the desirable growth compensation could be elicited through mild intermittent food-deprivation that incorporates one-day of feed-deprivation with one-day of re-feeding.
Hyperthermy stress is a common environmental condition in the cultivation of red swamp crayfish, Procambarus clarkii that is a major economic crustacean in China. In this study, the reaction mechanism of the P. clarkii to hyperthermal stress at 35 °C for 25 days was explored by investigating the survival rate, hepatopancreas histopathology and intestinal microbial responses. The results indicated that under the hyperthermy stress the survival rate significantly reduced, the hepatopancreas tissue structure was severely damaged including hepatocyte vacuolization and enlarged lumen, and which caused the disorder of intestinal flora. High-throughput 16S ribosomal DNA (rDNA) sequencing revealed that the hyperthermy stress significantly reduced intestinal microbial diversity and altered microbial composition. Specifically, Proteobacteria and Firmicutes were significantly decreased, Bacteroidota (mainly Bacteroides) and Fusobacteriota (mainly Fusobacterium) were significantly increased. The abundance of the beneficial bacterium Citrobacter decreased while that of the pathogenic bacterium Shewanella increased. PICRUSt functional prediction analysis showed that the hyperthermy stress could significantly alter pathways related to Organismal Systems and Environmental Information Processing, and significantly decreased pathways associated with Metabolism, Cellular Processes, and Genetic Information Processing. In conclusion, sustained hyperthermy stress (35 °C) for 25 d caused adverse effects on P. clarkii. Our study revealed the response mechanism of P. clarkii to hyperthermy stress, which can provide a theoretical basis for better understanding the healthy culture of this crayfish in high temperature season.
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