Potential risk assessment of different sizes of microplastics on the digestive system of hybrid sturgeon

Abstract

Microplastics are pollutants that are widely present in aquatic environments. This study utilized polyethylene microplastic particles of 1 μm and 5 μm to expose hybrid sturgeon (Acipenser baerii ♂ × A. schrenckii ♀), analyzing changes in intestinal ultrastructure, digestive enzyme activity, and gut microbial composition (based on high-throughput sequencing of the 16S rRNA V3–V4 region). The results indicate that MPs of both particle sizes cause changes in intestinal ultrastructure and digestive enzyme activity. The alpha and beta diversity of gut microbiota in the exposed groups were significantly higher than those in the control group. At the phylum level, the relative abundances of Bacteroidetes, Actinobacteria, and Desulfobacterota significantly increased (P < 0.01); at the genus level, the abundances of Pseudomonas, Lactobacillus, Enterobacter, Desulfovibrio, HIMB11, and Muribaculaceae also significantly increased (P < 0.01). Furthermore, functional predictions of the microbiota indicated that the abundance of functions related to diseases, cellular processes, and organism systems increased in the 5 μm treatment group, while the abundance of functions related to genetic information processing significantly decreased (P < 0.05, FDR < 0.05). This study reveals the potential risks of MPs to the digestive physiology and intestinal digestive system of sturgeon, providing a basis for further exploration of the mechanisms by which different particle sizes of MPs affect freshwater fish.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10653-026-03028-8.

Introduction

Microplastics refer to plastic particles with a diameter of less than 5 mm, which are ubiquitous in marine and terrestrial ecosystems, including various foods, drinking water, and air (Duong et al., 2025; Singh & Yadav, 2025). These particles can be easily inhaled or ingested, leading to oxidative stress, inflammatory responses, and metabolic disorders (Chen et al., 2022). MPs typically originate from cosmetics, textiles, and plastic packaging (Izlal et al., 2025), and are often inert materials that can break down into smaller fragments due to environmental interactions. They have the capacity to adsorb a range of persistent organic pollutants and potentially toxic elements, such as polychlorinated biphenyls polycyclic aromatic hydrocarbons, Fe, and Pb, resulting in lasting impacts on the environment and living organisms (Liu et al., 2025; Priya et al., 2022; Saha et al., 2025). Research indicates that aged MPs enhance their selective adsorption capacity through surface oxygen-containing functional groups, serve as a source of free radicals, increase environmental oxidative conditions, and even affect the expression of antibiotic resistance genes, thereby significantly altering their environmental behavior and ecological risks (Li et al., 2025). The intestine is an important digestive organ in animals, containing a variety of microbial communities, including bacteria, fungi, archaea, and viruses, collectively referred to as the gut microbiota (Antfolk & Jensen, 2020). The ingestion of MPs by animals may lead to intestinal tissue damage, alterations in intestinal enzyme activity, and even changes in the composition of gut microbiota, thereby affecting digestive function (Gu et al., 2020a, 2020b). α-amylase, trypsin, and lipase are key digestive enzymes responsible for breaking down carbohydrates, proteins, and fats, respectively. Changes in the activity of these enzymes can serve as direct indicators of how microplastic exposure affects the intestinal digestive capacity of fish (Ko et al., 2020).

MPs not only pose a threat to aquatic environments but can also endanger human health through the bioaccumulation process within the food chain (Yuan et al., 2022). Currently, researchers have detected the presence of MPs in various human organs, including the liver, small intestine, and kidneys (Cao et al., 2025). Studies have found that MPs can damage the intestinal barrier, hepatocytes, and the central nervous system, causing irreversible harm to the human body (Parkhurst et al., 2025; Zha et al., 2024; Liu et al., 2023). Particle size is a key factor influencing the toxicity of MPs. Research on zebrafish indicates that exposure to polystyrene MPs of different sizes can have varying degrees of adverse effects on the species. Specifically, the smallest MPs (0.1 μm) significantly impact the diversity of the intestinal microbiota in zebrafish. Furthermore, compared to larger sizes (5 μm and 200 μm), smaller MPs (100 nm) have been shown to modify the expression of genes associated with the production of reactive oxygen species (Gu et al., 2020a, 2020b; Yu et al., 2023). While the ecological toxicity of microplastics has been widely recognized, the size-dependent mechanisms underlying their toxic effects, particularly in economically and ecologically valuable freshwater fish species, remain insufficiently elucidated.

Sturgeons primarily inhabit cold water environments. Caviar, commonly referred to as 'black gold', originates from sturgeons and is one of the most economically valuable fish products globally. The Siberian hybrid sturgeon is a hybrid offspring of the Acipenser baerii (♂) and A. schrenckii (♀). It inherits the robust disease resistance and transportability from the paternal lineage, along with the rapid growth characteristics from the maternal lineage (Zhao et al., 2022). The artificial freshwater sturgeon farming in China has seen substantial output, with extensive use of plastic products. China's artificial freshwater sturgeon farming has achieved substantial production output. The use of aquaculture tools and feed during the farming process may contribute to the accumulation of microplastics. This poses a potential risk to the quality of sturgeon-derived products, which could ultimately lead to economic losses. Due to its long lifecycle and benthic habits, the hybrid sturgeon is highly likely to act as an efficient accumulator of microplastics in aquatic environments. Moreover, its high-value derivatives, such as caviar, are directly linked to human consumption, making it particularly urgent to investigate the bioaccumulation effects of microplastics in this species and their impacts on digestive health. Therefore, this study focuses on the hybrid sturgeons bred and raised in Sichuan Province, investigating the effects of polyethylene MPs of different particle sizes on intestinal tissue morphology, digestive enzyme activity, and gut microbiota. The aim is to provide scientific data for further research on the toxic mechanisms of MPs on freshwater fish such as sturgeons.

Materials and methods

Experimental animals and MPs challenge

Siberian hybrid sturgeon fry was collected from April to July 2022, sourced from the healthy hybrid sturgeon cultivated at the Pengzhou base of Sichuan Runzhao Fisheries Co., Ltd. They were reared in 30-L aquariums at the College of Life Sciences, Sichuan Agricultural University, with the water temperature maintained at 20 °C for two weeks. Polyethylene MPs were purchased from Zhengmei Plastic Products Co., Ltd. (Zhengzhou, China), and feed binders were sourced from Future Water World Biotechnology Co., Ltd. (Zhenjiang, China). Commercial sturgeon feed was crushed and mixed with microplastic powder at a ratio of 20% by weight, based on previous studies which demonstrated significant toxic effects at this concentration in aquatic and insect models, and then dried at 60 °C (Wang, 2019; Tang et al., 2020). According to published studies, significant potential concentrations of MPs that pose harm to aquatic organisms have been reported (Wang Yongjin et al., 2019; Tang et al., 2020). A total of 90 sturgeons, weighing approximately 20 ± 5 g and of similar weight, were randomly divided into three groups, each containing 30 fish. The sturgeons were fed with feed that did not contain polyethylene MPs (PE0 group), feed with 1 micron polyethylene MPs (PE1 group), and feed with 5micron polyethylene MPs (PE5 group) for a duration of 30 days. As reported by Wang et al., (2021a, 2021b), the feeding regime consisted of a daily provision of feed amounting to 1% of the sturgeon's body weight. The growth and mortality rates of the sturgeons were closely monitored.

Sample collection

After 30 days of feeding treatment, ten fish were randomly selected from each group and anesthetized with MS-222. The Siberian sturgeon hybrids were dissected, and the intestines were rinsed with PBS. The spiral intestine segment was cut open, and the intestinal contents were collected and immediately snap-frozen in liquid nitrogen for preservation. The samples were then stored in a − 80 ℃ freezer.To maintain the integrity of intestinal cells, a small section of intestinal tissue was fixed in 4% paraformaldehyde for 24 h for subsequent histological observation.

Measurements of intestinal morphology

Samples of the intestinal tract from hybrid sturgeon were collected and prepared into paraffin sections. The fixed intestinal samples were rinsed with PBS, dehydrated through a graded alcohol series, cleared in xylene, and embedded in paraffin wax. Sections of 5 µm thickness were prepared and stained with hematoxylin and eosin (H&E), followed by mounting with neutral resin. Subsequently, the sections were observed under a Nikon Eclipse 80i microscope, and villus height and muscularis thickness were measured using Fiji Image J software. The obtained data were presented as error bar charts generated with GraphPad Prism 10.4.1, with results expressed as mean ± standard deviation (mean ± SD). Statistical analysis was performed using one-way analysis of variance (one-way ANOVA), and differences between groups were analyzed with the t-test. Mean comparisons were further conducted using Duncan's multiple comparison test.

Assessment of α-amylase, trypsin and lipase enzyme activity

The specific enzyme activity assay kits were purchased from Kemin Biotechnology Co., Ltd. α-AMS (DFMA-2-Y) α-amylase (Suzhou, China), trypsin (YPT-2-W), and lipase (LPS-2-W) were used to determine the activities of α-amylase, trypsin, and lipase in the intestine. Approximately 0.1 g of intestinal tissue from the segment was homogenized in 0.9 mL of 0.65% NaCl solution using a cold homogenizer. Following the instructions of the assay kits, enzyme activities were measured using a spectrophotometer. All experimental data from digestive enzyme activity assays are expressed as mean ± standard deviation. Error bar charts were generated using GraphPad Prism 10.4.1. Differences between groups were analyzed by one-way analysis of variance (ANOVA) followed by Duncan's test, with statistical significance set at P < 0.05.

Microbial composition and diversity analysis

The gut microbiota analysis was conducted by BGI Genomics Co., Ltd. (Shenzhen, China). Intestinal contents were aseptically collected from six randomly selected Siberian sturgeon hybrids. Total genomic DNA was extracted using the MagPure Stool DNA KF Kit B according to the manufacturer’s instructions. DNA concentration and purity were measured with a NanoDrop 2000, and integrity was assessed by 1% agarose gel electrophoresis. Following the protocol described by Adams et al., (2013). PCR amplification was performed with primers 338F (5′-ACTCCTACGGGAGGCAGCAG-3′) and 806R (5′-GGACTACHVGGGTWTCTAAT-3′) targeting the V3–V4 hypervariable regions of the bacterial 16S rRNA gene. Amplified products were purified using DNA selection beads and used for library construction. Library quality was evaluated with an Agilent 2100 Bioanalyzer to confirm fragment size distribution and concentration. Qualified libraries were subjected to paired-end sequencing on the DNBSEQ-2000 platform.

Raw sequencing reads were processed by removing primer sequences with Cut Adapt and filtering out reads shorter than 50 bp, those containing ambiguous bases (> 20%), or those with adapter contamination (He et al., 2013). High-quality paired-end reads were merged using FLASH under the following parameters: minimum overlap of 10 bp and maximum mismatch rate in the overlap region of 0.2. The resulting clean tags were denoised with the DADA2 algorithm in the QIIME2 pipeline to generate amplicon sequence variants (ASVs). Taxonomic assignment of ASV representative sequences was performed using the RDP Classifier with a confidence threshold of 0.6. ASVs that were unclassified or assigned to non-bacterial domains were removed from downstream analyses. α-Diversity within samples was calculated with Mothur (Schloss et al., 2009). β-Diversity between samples was assessed using QIIME and visualized via principal coordinate analysis (PCoA). Taxonomic composition at the phylum and genus levels was analyzed and plotted with R and the gplots package. Differentially abundant taxa across groups were identified with linear discriminant analysis effect size (LEfSe), which incorporates Kruskal–Wallis and Wilcoxon tests. Finally, PICRUSt2 was applied to predict the functional potential of the microbial communities.

Results

Intestinal fold height and muscularis thickness

The histological examination revealed that all fish showed no visible pathological changes in their intestines. The intestinal contents were deep brown, uniform, and viscous, with no other abnormal components such as undigested feed chunks or visible microplastic and adhesive aggregates. Quantitative measurements of the intestinal morphological structure indicated that the thickness of the muscular layer in the PE1 group was significantly thinner compared to the PE0 and PE5 groups (P < 0.05) (Fig. 1a), while there were no significant differences in villus length among the groups.

Fig. 1.

Effects of microplastic particle size on intestinal fold height and muscularis thickness in hybrid sturgeon (*P < 0.05, **P < 0.01)

Activities of the digestive enzymes of α-amylase, trypsin and lipase

The intestinal α-amylase activity in the PE1 group (0.0124 ± 0.0022 μmol/min/mg) was significantly higher than that in the PE0 group (0.0070 ± 0.0015 μmol/min/mg) and the PE5 group (0.0070 ± 0.0012 μmol/min/mg) (P < 0.01) (Fig. 2a). Compared to the PE0 group (0.0332 ± 0.0222 U/mg) and the PE5 group (0.0270 ± 0.0071 U/mg), the intestinal trypsin activity in the PE1 group (0.0765 ± 0.0334 U/mg) was also significantly elevated (P < 0.05) (Fig. 2b). The intestinal lipase activities in the PE0 group (0.1339 ± 0.0202 μmol/min/mg), PE1 group (0.2751 ± 0.2155 μmol/min/mg), and PE5 group (0.1786 ± 0.0810 μmol/min/mg) exhibited a consistent trend with that of α-amylase (P < 0.01) (Fig. 2c).

Fig. 2.

Effect of MPs on digestive enzyme activity of hybrid sturgeon (*P < 0.05, **P < 0.01)

Microbial composition and diversity

A total of 232 amplicon sequence variants (ASVs) were obtained from the co-aggregation category. Notably, the PE5 group exhibited the highest ASV count (192), including 168 unique ASVs. In contrast, the PE1 group contained 52 ASVs, of which 24 were unique, while the PE0 group had only 29 ASVs, with 8 being unique. A total of 13 ASVs were shared among the three groups (Fig. 3). Alpha diversity analysis (Fig. 4a–e) indicated Compared to the PE0 group, the PE1 group showed a significant decrease only in the Shannon index (*P = 0.032), with no significant differences observed in the Sobs, Ace, Chao, and Simpson indices (*P > 0.05).In contrast, the PE5 group exhibited more pronounced alterations in diversity: the Sobs, Ace, and Chao indices were all extremely significantly decreased (P < 0.001), the Shannon index was highly significantly decreased (P = 0.005), and the Simpson index was significantly increased (*P = 0.024). The PE-MPs feeding treatment enhanced the alpha diversity of the gut microbiota in hybrid sturgeon, with the PE5 group showing a more pronounced effect than the PE1 group. Beta diversity analysis (Supporting Information Fig. S1) shows that the Weighted Unifrac distance among the three groups reaches 0.4, while the unweighted Unifrac distance between the PE1 and PE0 groups is 0.7, and the Unifrac distance between the PE5 and PE0 groups is 0.8.

Fig. 3.

Gut microbial ASV composition in hybrid sturgeon under different treatments

Fig. 4.

Analysis of intestinal flora diversity of hybrid sturgeon after feeding different MPs (a–e) Box plots depicting alpha diversity differences among groups (*P < 0.05, **P < 0.01, ***P < 0.001)

Microbial relative abundance at the phylum and genus levels

At the phylum level (Fig. 5a), the PE0 and PE1 groups are primarily composed of Fusobacteriota (75.16% and 36.10%), Firmicutes (15.21% and 38.13%), and Proteobacteria (9.60% and 25.70%). In contrast, the PE5 group exhibits a different distribution with respect to Fusobacteriota (26.42%), Firmicutes (41.56%), and Proteobacteria (31.16%). Comparative analysis of key species (Fig. 5b) indicates that the abundance of Fusobacteriota in the PE0 group is significantly greater than that in the PE1 and PE5 groups (P < 0.01). Moreover, significant differences are also observed among the three groups for Bacteroidota, Actinobacteriota, and Desulfobacterota (P < 0.01), as well as Cyanobacteria (P < 0.05). At the genus level (Fig. 5c), the PE0 group was dominated by the genera Neisseria (9.55%), Clostridium (10.59%), and Bacteroides (75.16%). In the PE1 and PE5 groups, the dominant genera included Neisseria (25.55% and 28.54%), Clostridium (35.03% and 37.59%), Bacteroides (36.10% and 26.42%), and Pseudomonas (0.039% and 1.90%). A comparison of key species (Fig. 5d) revealed that the abundance of Bacteroides in the PE0 group was significantly higher than that in the PE1 and PE5 groups (P < 0.01). Significant differences were also observed among the three groups for Pseudomonas (P < 0.01), Lactobacillus, Faecalibaculum, Dubosiella, HIMB11, Muribaculaceae (P < 0.01), and Clostridium (P < 0.05). There are no significant differences in the classification levels of other taxa. The LEfSe analysis results (Supporting Information Fig. S2) indicate that there are multiple statistically significant microbial communities among the three groups (LDA score > 2). Specifically, the biomarkers of the PE0 group are concentrated in Fusobacteriota. Compared to the control group, the biomarkers of the PE1 group are enriched in the phylum Firmicutes and the phylum Pseudomonas, while the biomarkers of the PE5 group are enriched in the phyla Firmicutes, Bacteroidota, Actinobacteriota, and Desulfobacterota, among others.

Fig. 5.

Analysis of species composition of intestinal flora in hybrid sturgeon groups after MPs ingestion a Species composition histogram at the phylum level. b Histogram of key differential species at the phylum level. c Species composition histogram at the genus level. d Histogram of key differential species at the genus level

Predicted function and characteristics of microbiota

According to the KEGG level 1 abundance analysis (Supporting Information Fig. S3), the primary functions of the hybrid sturgeon gut microbiota are related to metabolism, genetic information processing, cellular processes, environmental information processing, and additional categories. The KEGG level 1 functional differential analysis indicates that, compared to the PE0 group, the PE1 group exhibits higher abundances of cellular processes, organismal systems, environmental information processing, and disease-related functions, while showing lower abundances of genetic information processing and metabolism-related functions; however, these differences are not statistically significant (Fig. 6a). In contrast, compared to the PE0 group, the PE5 group shows increased functional abundances related to disease, cellular processes, and biological systems, accompanied by a significant decrease in functional abundances related to genetic information processing (Fig. 6b). The KEGG level 2 functional differential analysis reveals no significant changes in functional abundances between the PE0 and PE1 groups (Fig. 6c). However, compared to the PE0 group, the PE5 group exhibits significantly elevated functional abundances in signal transduction, infectious diseases: bacteria, immune system, lipid metabolism, biodegradation and metabolism of xenobiotics, cellular motility, and digestive system. Conversely, the PE5 group shows significantly reduced functional abundances in translation, folding, sorting and degradation, terpenoid and polyketide metabolism, as well as nucleotide metabolism (Fig. 6d).

Fig. 6.

Analysis of functional differences in intestinal flora of hybrid sturgeon after MPs ingestion. a Functional difference analysis between group PE0 and group PE1 at KEGG Level 1. b Functional difference analysis between the PE0 and PE5 groups at KEGG Leve l. c Functional difference analysis between the PE0 and PE1 groups at KEGG Level 2. d Functional difference analysis between the PE0 and PE5 groups at KEGG Level 2

Discussion

After ingesting MPs, aquatic organisms can retain these particles in their bodies for an extended period, exhibiting characteristics of resistance to digestion. The residual MPs not only cause physical damage to the intestine, triggering inflammatory responses, but also interfere with the normal absorption of nutrients. In a study investigating the effects of microplastic exposure on crucian carp, Mattsson et al. found that half of the individuals in the exposed group exhibited an increase in the thickness of the intestinal muscular layer, while the number of goblet cells at the tips of the villi decreased, indicating significant tissue damage (Mattsson et al., 2015). This study measured intestinal morphological structure indicators, revealing that the muscular layer thickness in the PE1 group was significantly lower than that in the PE0 and PE5 groups (P < 0.01). Notably, the results for the PE5 group were contrary to previous studies, which may be attributed to the fact that 1 μm microplastic particles are smaller than 5 μm particles, allowing for easier passage through the intestinal wall and deeper tissue infiltration (Stock et al., 2022; Zhu et al., 2024, 2025).

MPs can disrupt the homeostasis of the biological internal environment, affecting the composition and metabolic functions of gut microbiota, ultimately leading to dysbiosis and further interfering with digestive enzyme activity. Studies on Carassius auratus and Mytilus edulis have shown that exposure to MPs significantly alters the gut microbiota structure and markedly inhibits the activity of serum amylase and lipase in mussels, resulting in decreased digestive capacity (Hu et al., 2022; Wang et al., 2021a, 2021b). This study measured and compared the activities of α-amylase, trypsin, and lipase in the intestines of hybrid sturgeon across different treatment groups. The results indicated that the activities of these three digestive enzymes in the PE1 group were significantly higher than those in the PE0 and PE5 groups (P < 0.05). Combining this with the data on the thickness of the intestinal muscular layer, we speculate that this phenomenon arises from intestinal damage induced by MPs, which hinders the digestion and absorption of nutrients, leading to nutritional deficiency in the organism; in response to this deficiency, the organism may compensatorily increase digestive enzyme activity. In contrast, there were no significant differences in the activities of the three digestive enzymes between the PE0 and PE5 groups, a result that is inconsistent with the aforementioned studies. The reason for this discrepancy may be attributed to the smaller particle size of MPs, which possess a larger specific surface area and adsorption capacity, allowing for more effective interaction with digestive fluids, digestive enzymes, and intestinal epithelial cells (Jiang et al., 2025; Trestrail et al., 2021).

The microbial alterations identified in this study profoundly impacted the host's overall digestive physiology, an effect that exhibited particle-size dependence. A substantial body of evidence indicates that microplastics (MPs) can lead to an imbalance in the gut microbiota of animals (Lu et al., 2018; Jin et al., 2019). Studies on zebrafish, Oryzias melastigma and brine shrimp have shown that MPs can trigger dysbiosis in their gut microbiota, impair digestive system function, and affect normal feeding and nutrient absorption (Kang et al., 2021; Li et al., 2021; Wan et al., 2018). Consistent with previous research, this study found that microplastic treatment altered the community diversity, structural composition, and functional abundance of the gut microbiota in hybrid sturgeon, profoundly affecting its digestive physiology in a particle-size-dependent manner. At the phylum level, compared to the control group (PE0), the relative abundances of Firmicutes and Proteobacteria significantly increased in the PE1 and PE5 groups, while the abundance of Bacteroidetes significantly decreased. This structural shift may directly disrupt nutrient metabolism balance (Liao et al., 2024). At the genus level, key changes were further clarified: compared to the PE0 group, the abundance of Bacteroides significantly decreased in the PE1 and PE5 groups, whereas the abundances of Neisseria and Clostridium significantly increased. It is particularly noteworthy that Pseudomonas showed significant enrichment only in the PE5 group. LEfSe analysis further confirmed that the signature taxa in the PE1 group were concentrated in Firmicutes and the genus Pseudomonas, while the PE5 group additionally exhibited significant enrichment in taxa such as Desulfobacterota.

The gut microbiota plays a crucial role in enhancing host digestive capacity and immune response, which are essential for host metabolic health (Lynch & Pedersen, 2016; Karami et al., 2016). In this study, the decreased abundance of Bacteroides, a key genus for degrading complex polysaccharides, may directly impair intestinal carbohydrate fermentation and energy harvest efficiency (David et al., 2017; Cheng et al., 2022), thereby affecting the host's digestive physiology. Concurrently, dysbiosis may trigger obesity and a range of harmful physiological consequences, including epithelial damage, intestinal inflammation, and oxidative stress (Chen et al., 2017; Lei et al., 2018). The specific enrichment of Pseudomonas (an opportunistic pathogen) and Desulfobacterota in the PE5 group may synergistically promote the accumulation of potentially harmful metabolites (such as hydrogen sulfide) in the gut, thereby exacerbating epithelial barrier damage and inflammation risk (Lin & Kazmierczak, 2017; Rao et al., 2021; Wei et al., 2024). This finding is consistent with research on guppies, in which polystyrene microplastics were shown to suppress the metabolic and repair pathways of the gut microbiota (Huang et al., 2020). Together, these results indicate that microplastics of different particle sizes systematically disrupt the host's digestive physiology through alterations in the gut microbiota structure, affecting processes such as nutrient breakdown, barrier integrity, and immune homeostasis.

Based on the predictive analysis of bacterial community functional abundance, this study found that after treatment with MPs, the functional abundance related to diseases, cellular processes, biological systems, and environmental information processing increased in the gut microbiome of hybrid sturgeon, while the abundance of functions related to genetic information processing and metabolism decreased. Additionally, the relative abundance of gut pathogens such as Desulfobacterota increased, with a corresponding enhancement in functions related to bacterial infection, the immune system, lipid metabolism, and the endocrine system. Conversely, the functional abundance associated with nucleotide metabolism, glycan biosynthesis and metabolism, and carbohydrate metabolism decreased. These changes may collectively lead to various adverse physiological responses in sturgeon (Lu et al., 2016). The toxic effects of MPs exhibit size and species dependence. Studies on the Brachionus koreanus and adult male zebrafish indicate that smaller-sized polystyrene MPs are more readily expelled by rotifers than larger-sized particles, significantly activating the mRNA and protein expression of factors such as IL1α, IL1β, and IFN in the gut. The negative effects of MPs, such as stunted growth, decreased reproductive capacity, shortened lifespan, and prolonged reproductive cycles, are closely related to their particle size, with smaller MPs generally exhibiting greater toxicity (Jeong et al., 2016; Jin et al., 2018). However, this study demonstrates that the 5 μm microplastic treatment group had a more significant impact on the diversity, community composition, and function of the gut microbiota in hybrid sturgeon compared to the 1 μm group. This finding contrasts with the observations of intestinal ultrastructure and digestive enzyme activity. Such apparent discrepancy suggests that microplastics of different sizes may disrupt intestinal homeostasis through distinct mechanistic pathways, as discussed above: 1 μm microplastics, due to their smaller size, are more likely to directly interact with the intestinal epithelium, causing physical damage and directly impairing digestive function. In contrast, 5 μm particles may be more readily retained by the mucus layer or serve as colonization substrates for microorganisms, thereby exerting a more persistent disruption on microbiota composition and function (Zhang et al., 2023; Gong et al., 2023). This size-dependent divergence in toxic pathways indicates that the impacts of microplastics on organisms are multifaceted and complex, necessitating multidimensional assessments in future studies to fully elucidate their toxicological mechanisms.

The findings from this 30-day study, using only two small microplastic sizes, reveal initial intestinal damage in sturgeon. Provide initial insights into intestinal damage and responses in sturgeon. However, they may not fully capture the profound dynamics of the gut microbiota under prolonged exposure or reflect the potential effects of larger microplastic particles. Future research should therefore systematically investigate the chronic cumulative effects of microplastics across extended exposure durations and a broader size range. Integrating multi‑omics approaches will help elucidate the underlying toxicological mechanisms in sturgeon, thereby offering a more comprehensive scientific basis for ecological risk assessment.

Conclusion

This study investigates the effects of microplastics of different particle sizes on the digestive system of hybrid sturgeon. The results indicate that microplastics can alter the ultrastructure of the intestine, the activity of digestive enzymes, and the composition of microbial communities. Notably, the treatment with 1 μm microplastics had a more significant impact on intestinal morphology and digestive enzyme activity, while 5 μm microplastics exhibited a more pronounced disruptive effect on gut microbiota structure and function. These findings contribute to a deeper understanding of the impact of microplastics on the gut microecology of sturgeon.

Supplementary Information

Below is the link to the electronic supplementary material.

Authors contribution

Wu JY, Liao QQ, Ren YY, and Senggen RB conceived and conducted the experiment. Liao QQ, Ren YY, Deng CW, Li YK, Du XG and Yang SY performed the data reduction. Liao QQ, Wang C and Yang Y analyzed the results. Liao QQ and Wu JY wrote the manuscript. The project was performed under the supervision of Yang SY. All authors reviewed the manuscript.

Funding

This study was funded by the Program in Breeding of Aquatic Animals of Sichuan Province (2026-2030), the Sichuan Science and Technology Program (2021YFYZ0015), Sichuan Innovation Team Project of the National Modern Agricultural Industry System (SCCXTD-2026-15), and Sichuan Key Waters Aquatic Life Monitoring and Fishing Ban Effect Evaluation Project (2024 & 2025) of the Yangtze River Basin.

Data availability

The data that support the findings of this study are available in the Additional files of this article.

Declarations

Ethics statement

The animal use protocol listed below has been reviewed and approved by the Sichuan Agricultural University Animal Ethical and Welfare Committee (Approval No. 20230130).

Competing interest

The authors declare no competing interests.