Microplastics in different tissues of historical and live samples of endangered mega-fish (Acipenser sinensis) and their potential relevance to exposure pathways.

The Chinese sturgeon (Acipenser sinensis) is an endangered freshwater mega-fish (IUCN-red listed) that survives in the Yangtze River Basin, but the population of which has declined significantly in response to environmental pressures generated by human activities. In order to evaluate the interaction between Chinese sturgeon and microplastics (MPs) for the first time, we examined the gut and gills of historical samples (n = 27), in conjunction with the blood and mucus of live samples (n = 10), to explore the potential pathways involved in MP uptake. We detected MPs in 62.9 % of the field fish, with no significant difference between guts (mean=0.9 items/individual) and gills (mean=0.8 items/individual). The abundance of MPs in fish from 2017 was significantly higher than that from 2015 to 2016 with regards to both gills and gut samples. The size of MPs in gills was significantly smaller than those in guts, yet both contained mostly fibers (90.2 %). No MPs were confirmed in blood, however 62.5 % of mucus samples contained MPs. The MPs in mucus indicated the possibility of MPs entering Chinese sturgeons if their skins were damaged. The body size of Chinese sturgeons affected their MPs uptake by ingestion and inhalation, as less MPs were detected in the gut and gills of smaller individuals. Combining the evidence from historical and live samples, we revealed the presence of MPs in different tissues of Chinese sturgeon and their potential relevance to exposure pathways. Our work expands the understanding of multiple exposure pathways between MPs and long-lived mega-fish, while emphasizing the potential risks of long-term exposure in the field.

Effects of Citrobacter freundii on sturgeon: Insights from skin mucosal immunology and microbiota.

Skin mucus analysis has recently been used as a non-invasive method to evaluate for fish welfare. The present research study was conducted to examine the skin mucosal immunity and skin microbiota profiles of sturgeons infected with Citrobacter freundii. Our histology results showed that the thickness of the epidermal layer of skin remained thinner, and the number of mucous cells was significantly decreased in sturgeons after infection (p < 0.05). Total protein, alanine aminotransferase, aspartate aminotransferase, superoxide dismutase, and creatine kinase levels in the mucus showed biphasic pattern (decrease and then increase). Lactate dehydrogenase, lysozyme, and acid phosphatase activities in the mucus showed an increasing trend after infection. Furthermore, 16S rRNA sequencing also revealed that C. freundii infection also affected the diversity and community structure of the skin mucus microbiota. An increase in microbial diversity (p > 0.05) and a decrease in microbial abundance (p < 0.05) after infection were noted. The predominant bacterial phyla in the skin mucus were Proteobacteria, Fusobacteria, Bacteroidetes, Firmicutes, and Actinobacteria. Specifically, the relative abundance of Fusobacteria increased after infection. The predominant bacterial genera in the skin mucus were Cetobacterium, Pelomonas, Bradyrhizobium, Flavobacterium, and Pseudomonas. The relative abundance of Cetobacterium, Pseudomonas, and Flavobacterium increased after infection. Our current research findings will provide new insights into the theoretical basis for future research studies exploring the mechanism of sturgeon infection with C. freundii.

Indexing serum and mucous biochemical parameters of endangered Chinese sturgeon Acipenser sinensis with implications for health assessment.

The Chinese sturgeon (Acipenser sinensis) is a critically endangered aquatic fish. Health monitoring and welfare assessments are critical for the conservation of Chinese sturgeon. In this study, biochemical parameters of serum and skin mucus in Chinese sturgeon were examined to evaluate the potential biomarkers. Serum and mucous samples were obtained from Chinese sturgeon, and the levels of total protein (TP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), creatine kinase (CK), lactic acid (LD), acid phosphatase (ACP), lysozyme (LYZ), glucose (GLU), and cortisol were determined. The concentrations of ALT, AST, cortisol, and LYZ were significantly higher in the mucous group than those in the serum group (p < 0.05). In addition, the concentrations of ALP, ACP, LD, LDH, CK, and TP were significantly higher level in the serum group than those in the mucous group (p < 0.05). Moreover, the correlations between serum and mucous biochemical parameters were established. Statistical analysis showed a positive correlation between serum and skin mucous markers (ACP, cortisol, and LYZ). AST versus ALT in serum and mucus showed a significant positive correlation (p < 0.01). A significant positive correlation was found between cortisol and CK in mucus (p < 0.01). Moreover, LD versus LDH in serum showed a significant but weak positive correlation (p < 0.01). Principal component analysis revealed a complete separation between the serum and mucous groups, with the biomarkers that contributed the most being ALP, TP, ALT, and AST. This study provides baseline data and reference intervals for serum and mucous biochemical parameters in presumably healthy Chinese sturgeons. The current study has important implications for the development of conservation strategies and the conservation status of critically endangered species.

Multi-omics reveals response mechanism of liver metabolism of hybrid sturgeon under ship noise stress.

Underwater noise from ship engines can affect the metabolism and immune system of various fish species. Meanwhile, changes in the metabolic pathways in liver are important for fish to adapt to adverse environments. We used a combined multi-omics analysis to investigate the response mechanism of hybrid sturgeon to continuously played ship noise. A control group and a noise group (simulated ship noise: 12 h) were set up, and liver tissues were extracted for high-throughput transcriptome and metabolome sequencing. The results show that a total of 588 differentially expressed genes (DEGs) and 58 DEGs metabolites were detected. The joint analysis of transcriptome and metabolome showed that under noise stress, apoptosis and cell motility were intensified, DNA replication, RNA transcription and translation, and protein synthesis were inhibited, and lipid metabolism, nucleotide metabolism, and vitamin D3 metabolic pathways were also inhibited. Interestingly, the initiation of a partial immune responses ensured their normal immunity abilities. Moreover, material and energy requirements of the organism under noise stress were guaranteed by upregulation of carbohydrate and amino acid metabolic pathways.

Seasonal Changes of Growth, Immune Parameters and Liver Function in Wild Chinese Sturgeons Under Indoor Conditions: Implication for Artificial Rearing.

Seasonality has a significant effect on the physiology of fish, especially the effect of water temperature changes. In the present study, the growth, innate immune parameters and liver function indices of two rescued wild adult Chinese sturgeons under captive conditions were monitored for 1 year. The results showed that the total annual weight loss rate of the male was -4.58% and the total weight gain rate of the female was 24.12%, in which the weight of both individuals registered highly significant differences in summer, fall and winter (p < 0.01). The male Chinese sturgeon also exhibited negative specific growth rates (-0.1 to -0.8%) during spring to fall, whereas positive specific growth rates, ranging from 0.03 to 0.11%, were recorded in the female. Seasonality also affected the innate immune parameters of the two Chinese sturgeons, in which leukocytes had been increasing since spring and C-reactive protein (CRP) content was significantly higher (p < 0.05) in summer than fall in both individuals. The CRP level of the male Chinese sturgeon showed a significant increase from fall to winter (p < 0.05), suggesting that it may have contracted infection or inflammation during this study period. With the analysis of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), transaminase (AST:ALT) ratio, alkaline phosphatase, albumin to globulin ratio and triglycerides, it was found that the liver function of the captive Chinese sturgeons was adversely affected along seasonal changes, with the highest degree of liver impairment in winter. In combining observations from growth performance and changes in innate immune and liver function parameters, the present findings deduced that the male Chinese sturgeon under study was more susceptible to seasonal changes than the female. For better indoor culture of adult Chinese sturgeons, monitoring of hematological parameters to detect early signs of inflammation and liver function abnormality should be conducted with routine veterinary care during prolonged captivity.

Assessing the genetic diversity of the critically endangered Chinese sturgeon Acipenser sinensis using mitochondrial markers and genome-wide single-nucleotide polymorphisms from RAD-seq.

As a living fossil, the endangered Chinese sturgeon (Acipenser sinensis) has been considered a national treasure in China. Here, the famous Gezhouba Dam and Three Gorges Dam on the Yangtze River were built in 1988 and 2006, for economic purposes. The natural population of Chinese sturgeon has declined since then, as these dams block its migratory route to the original spawning grounds in the middle reaches of the Yangtze River. In 2013 and 2014, there was an absence of spawning where it typically happened near the Gezhouba Dam. Nevertheless, from April to June in 2015, over 1,000 larvae with different body lengths (10-35 cm) were detected along the Shanghai Yangtze Estuary; but only little is currently known about the population genetic structure of the Chinese sturgeon. Herein, we inferred population genetic parameters from 462 available Chinese sturgeon specimens based on a 421-bp fragment of the mitochondrial DNA (mtDNA) D-loop region and 1,481,620 SNPs (single-nucleotide polymorphisms) generated by restriction site-associated DNA sequencing (RAD-seq). For the D-loop dataset, 15 haplotypes were determined. Randomly picked 23 individuals, representing the 15 D-loop haplotype groups, were subsequently used for further RAD-seq validation. The average nucleotide diversity calculated from the mtDNA and RAD datasets was 0.0086 and 0.000478, respectively. The overall effective female population size was calculated to be 1,255 to 2,607, and the long-term effective population size was estimated to range from 11,950 to 119,500. We observed that the genetic variability and the effective female population size of the current population in the Yangtze River are severely low, which are similar to the data reported over 10 years ago. The deduced relatively small effective population of female fish, limiting the genetic connectivity among Chinese sturgeon, should be considered a serious threat to this endangered species.