Effect of arsenic stress on the intestinal structural integrity and intestinal flora abundance of Cyprinus carpio

Aquatic organisms such as fish can accumulate high concentrations of arsenic (As), which has toxic effects on fish. However, whether the intestinal flora are involved in As damage to fish intestinal tissues and the underlying process are unclear. Common carp (Cyprinus carpio) were exposed to As (2.83 mg/L) in water for 30 days, and blood, muscle, intestine, and intestine samples were collected. Intestinal pathological sections were observed, and the lipopolysaccharide (LPS) levels in serum and the levels of As accumulation and tight junction-related factors in intestinal tissues were measured. The gut microbiota was analysed by 16S rRNA sequencing. The results showed that As treatment decreased the abundance of microbiota, increased the number of harmful bacteria, and decreased the number of beneficial bacteria in the intestine. In our experiment, the top 30 harmful and beneficial bacteria with the highest relative abundance were identified. Among the top 30 harmful and beneficial bacteria, As treatment resulted in a significant (P < 0.05) increase in harmful bacteria (such as Fusobacteriota, Bacteroidota (LPS-producing bacteria), Verrucomicrobiota, Bacteroides, Aeromonas, and Stenotrophomonas) and a significant (P < 0.05) decrease in beneficial bacteria (such as Actinobacteriota, Planctomycetota, Firmicutes, Reyranella, Akkermansia, and Pseudorhodobacter), which further demonstrated that As affects the abundance of intestinal flora. In addition, As exposure increased the LPS level in serum and the abundance of Bacteroidota (LPS-producing bacteria) in the intestine. Bacteroidota exhibits the six highest relative abundance at the phylum level, which indicates that LPS produced by Bacteroidota can increase the LPS level in serum. Additionally, the protein and gene levels of the tight junction markers ZO-1 and occludin in the intestine were reduced by As treatment, which further indicated that As exposure impaired the structural integrity of the intestine. In conclusion, the results obtained in our study indicate that the intestinal flora, LPS, and tight junctions participate in the impairment of the structural integrity of the common carp intestine resulting from As exposure

Comparison genetic diversity and population structure of four Pseudaspius leptocephalus populations in Heilongjiang River Basin based on mitochondrial COI gene

The Pseudaspius leptocephalus is a unique fish in the Heilongjiang River Basin and has important economic and ecological value. In the present study, the complete mitochondrial genome of P. leptocephalus were determined, and COI partial sequences of 85 individuals from Erguna river (EH), Mohe (MH), Fuyuan (FY), Hulan (HL) were used to evaluated the genetic diversity of four populations of P. leptocephalus in Heilongjiang River Basin. The mitogenome is 16,607 bp in length and contained one D-loop, 2 rRNA, 13 PCG, and 22 tRNA. 4 variable sites and 5 haplotypes were detected in 705 bp COI, and 705 bp COI exhibited a lower content of C + G (45.95%) than A + T (54.05%). The nucleotide diversity (π) and haplotype diversity (h) indices ranged from 0.00027 (HL) to 0.00065 (EH and FY) and from 0.192 (HL) to 0.462 (EH), respectively. The genetic distance within the population and between populations ranged from 0.0006554 to 0.0002728 and from 0.0003541 to 0.0006974, respectively. Pairwise values of FST and Nm showed that there was moderate genetic differentiation between EH population and other populations and individuals between EH population and other populations can mate randomly (0.15 > FST > 0.05, Nm > 4). Significant negative values of neutrality tests (P < 0.05) indicated that MH and FY populations may had experienced population expansion, but mismatch distribution analysis suggested that all populations have remained basically stable. These results provide strong basis for the protection and utilization of P. leptocephalus germplasm resources, and provide valuable information for the population structure and genetic diversity of P. leptocephalus

Selenium-rich Lactobacillus plantarum alleviates salinity stress in Cyprinus carpio: Growth performance, oxidative stress, and immune and inflammatory responses

Salinity is an important environmental factor that affects the health of aquatic animals, when salinity level above the tolerance threshold can pose a significant threat to the survival of aquatic animals. As a trace element necessary for animal growth, selenium participates in the body’s antioxidant reaction, and protect aquatic animals from oxidative stress damage. Biological methods for synthesizing selenium nanoparticles (bio-Se-NPs) from bacteria are safe, inexpensive, and accessible. Therefore, we synthesized selenium nanoparticles using Lactobacillus plantarum (probiotic) to study the growth, immune, antioxidant, and inflammatory responses of selenium-rich Lactobacillus plantarum (SL, a type of bio-Se-NPs) fed Cyprinus carpio under low-salinity (5 g/L salinity) and high-salinity (10 g/L salinity) stresses. Analyses revealed that the addition of SL at a concentration of 1 mg/kg significantly alleviated the growth inhibition caused by high-salinity stress. SL significantly alleviated salinity-induced liver tissue injury (numerous cytoplasmic vacuolations the accumulation, inflammatory cell infiltration, nuclear lysis, and some blood congestion). SL significantly alleviated the abnormal levels of serum ALT, AST, GGT and LDH caused by salinity stress, and improved lipid metabolism (TG, TC, LDL-C, HDL-C). SL can also regulates cytokines and antioxidant genes (TNF-α, iL-1β, iL-10, TGFβ-1, SOD, CAT, GPx1, and HO-1) through the NF-κB and Nrf-2 signaling pathways and thereby reduce the inflammatory response and increase the antioxidant level, and these effects attenuate salinity-mediated oxidative damage. In conclusion, our findings indicate that SL can significantly promote the growth and development of fish and alleviate the adverse effects of high-salinity stress and thus, SL can be a potential feed additive for alleviating oxidative stress and inflammatory responses