Acute ammonia exposure has detrimental effects on shrimp, but the underlying mechanisms remain to be fully explored. In the present study, we investigated the impact of acute ammonia exposure on the gut microbiota of the white shrimp Litopenaeus vannamei and its association with shrimp mortality. Exposure to a lethal concentration of ammonia for 48 h resulted in increased mortality in L. vannamei, with severe damage to the hepatopancreas. Ammonia exposure led to a significant decrease in gut microbial diversity, along with the loss of beneficial bacterial taxa and the proliferation of pathogenic Vibrio strains. A phenotypic analysis revealed a transition from the dominance of aerobic to facultative anaerobic strains due to ammonia exposure. A functional analysis revealed that ammonia exposure led to an enrichment of genes related to biofilm formation, host colonization, and virulence pathogenicity. A species-level analysis and experiments suggest the key role of a Vibrio harveyi strain in causing shrimp disease and specificity under distinct environments. These findings provide new information on the mechanism of shrimp disease under environmental changes.

Environmental stressors such as nitrogen and phosphorus play a critical role in regulating the growth and physiological functions of Litopenaeus vannamei, a key species in aquaculture. This study investigates the effects of nitrogen and phosphorus stress on shrimp growth, oxidative stress, tissue damage, and molecular mechanisms. Exposure to increasing concentrations of nitrogen and phosphorus significantly reduced growth rates. Oxidative stress markers, including superoxide dismutase (SOD), catalase (CAT), total antioxidant capacity (T-AOC), and malondialdehyde (MDA), indicated heightened oxidative damage under both stress conditions, with nitrogen stress causing more severe responses than phosphorus stress. Histopathological analysis revealed substantial damage to the gills and hepatopancreas, organs essential for respiration and metabolism. Transcriptomic analysis identified differentially expressed genes (DEGs) enriched in apoptosis, lysosome, sphingolipid metabolism, and phagosome pathways, suggesting shared molecular responses to nitrogen and phosphorus stress. The results demonstrate that L. vannamei initiates oxidative and immune responses to cope with environmental stressors, but the adaptive capacity remains limited. These findings provide a foundation for understanding the stress tolerance mechanisms in shrimp and inform future strategies for breeding high-resistance strains in aquaculture.

Objective: In this study, a highly selective and sensitive LC-MS/MS method was developed to comprehensively analyze the distribution of astaxanthin across various tissues of Litopenaeus vannamei, as well as its variations in the hepatopancreas and ovary throughout ovarian development.Methods: The separation was performed on a BEH C8 column (1.7 μm, 2.1 × 50 mm) using a a gradient elution. The initial mobile phase composition was 0.1% formic acid in 3 mM ammonium acetate in water (solvent A) and methanol (solvent B) at a ratio of 15:85 (v/v), with a flow rate of 0.20 mL/min.Results: The assay demonstrated linearity over a concentration range of 20 to 10,000 ng/mL, with accuracy varying from −0.1 to 1.7% and precision within 2.1%. Using the established methodology, astaxanthin concentrations were quantitatively analyzed and comparatively assessed across various tissues of L. vannamei. Analytical results demonstrated that the ventral nerve cord and hepatopancreas exhibited the highest astaxanthin concentrations among all examined tissues, with values of 351 μg/g and 116 μg/g, respectively. During the ovarian developmental stages, astaxanthin was predominantly sequestered in the hepatopancreas during early phases, with concentrations ranging from 21.3 μg/g to 29.1 μg/g, representing a 43- to 59-fold increase compared to ovarian concentrations. However, a significant redistribution of astaxanthin was observed during the post-developmental stage, characterized by a substantial decrease to 5.74 μg/g in the hepatopancreas, concomitant with an increase to 7.47 μg/g in ovarian tissue.Conclusion: This validated LC-MS/MS method effectively quantified astaxanthin in various tissues of Litopenaeus vannamei, providing new insights into its tissue-specific distribution and potential role during ovarian development.

Paralytic shellfish toxins (PST) could be accumulated in bivalves and cause safety problems. To protect public health, bivalves are examined for PST contamination before entering the market, usually by high-performance liquid chromatography (HPLC) or LC-tandem mass spectrometry (LC-MS/MS) in the lab, which needs PST standards not all available and is time-consuming for large sample sizes. To detect PST toxicity in bivalves rapidly and sensitively, a biomarker gene is highly demanded, but the related study is very limited. In this study, we fed a commercially important bivalve, Patinopecten yessoensis, with the PST-producing dinoflagellate Alexandrium catenella. After 1, 3, and 5 days of exposure, both PST concentrations and toxicity levels in the digestive gland continuously increased. Transcriptome analysis revealed that the differentially expressed genes were significantly enriched in oxidation-reduction process, which included the cytochrome P450 genes (CYPs), type I iodothyronine deiodinase (IOD1s), peroxidasin (PXDN), and acyl-Coenzyme A oxidase 1 (ACOX1) at day 1 and a superoxide dismutase (SOD) at day 5, highlighting the crucial roles of these genes in response to oxidative stress induced by PST. Among the 33 continuously upregulated genes, five showed a significant correlation between gene expression and PST concentration, with the highest correlation present in PyC1QL4-1, the gene encoding Complement C1Q-like protein 4, C1QL4. In addition, the correlation between PyC1QL4-1 expression and PST toxicity was also the highest. Further analysis in another aquaculture scallop (Chlamys farreri) indicated that the expression of CfC1QL4-1, the homolog of PyC1QL4-1, also exhibited significant correlations with both PST toxicity and concentration. Our results reveal the gene expression responses of scallop digestive glands to PST-producing algae and indicate that the C1QL4-1 gene might be a potential biomarker for PST monitoring in scallops, which may provide a convenient way for the early warning and sensitive detection of PST contamination in the bivalves.

Cadmium (Cd) is a pervasive environmental pollutant that poses significant health risks to aquatic organisms, yet the functional role of metallothionein (MT) in mediating Cd tolerance in crustaceans beyond its use as a biomarker remains incompletely understood. In this study, we characterized a metallothionein gene (LvMT) from the Pacific white shrimp Litopenaeus vannamei and investigated its protective function against Cd-induced injury through integrated cellular, pathological, and transcriptomic approaches. LvMT protein exhibits typical structural features of crustacean MTs, with transcripts broadly distributed across tissues and highest abundance in the intestine, ventral nerve cord, brain, and hepatopancreas. In vitro, LvMT overexpression in HEK293T cells significantly enhanced cell viability under Cd, Zn, and H₂O₂ stress. In vivo, injection of recombinant LvMT-mCherry fusion protein improved shrimp survival under acute Cd challenge, attenuated Cd-induced histopathological damage in the hepatopancreas and gills, and partially restored antioxidant capacity. Transcriptomic analysis revealed that Cd exposure triggered early transcriptional responses involving xenobiotic metabolism, redox regulation, and metabolic disruption, whereas LvMT-associated transcriptional remodeling emerged at the later stage, characterized by the recovery of genes involved in protein synthesis, endoplasmic reticulum function, RNA turnover, energy production, and cellular maintenance. Temporal clustering further demonstrated that LvMT supplementation reversed the Cd-induced suppression of a large gene set associated with core cellular processes, facilitating the restoration of protein synthesis, energy production, and overall metabolic homeostasis. This study provides the first direct in vivo functional evidence that LvMT actively contributes to Cd tolerance in L. vannamei, highlighting its role as a protective regulator rather than merely a stress indicator, and offers mechanistic insights into MT-mediated cytoprotection in crustaceans.