Analysis of Acute Nitrite Exposure on Physiological Stress Response, Oxidative Stress, Gill Tissue Morphology and Immune Response of Large Yellow Croaker (Larimichthys crocea)

Assessing the Combined Toxicity of Silver and Copper Nanoparticles in Rainbow Trout (Oncorhynchus mykiss) Fingerlings

The growing use of silver (Ag) and copper (Cu) nanoparticles (NPs) for their antimicrobial properties has raised environmental health concerns due to their coexistence in aquatic ecosystems. This study assessed the combined physiological and molecular toxicity of AgNPs and CuNPs in rainbow trout (Oncorhynchus mykiss) exposed to sub-lethal concentrations of the NP mixture for 21 days. Fish were exposed to varying concentrations of co-exposure of AgNPs and CuNPs (T1 group 0.2 AgNPs + 0.2 mg/L CuNPs, T2 group 0.8 AgNPs + 0.6 mg/L CuNPs, and T3 group 1.4 AgNPs + 1.0 mg/L CuNPs). Behavioral alterations were evident, accompanied by a significant (p < 0.05) reduction in hemoglobin, red blood cell count, and hematocrit levels, while white blood cell counts increased, indicating immune activation. Serum biochemical analyses revealed metabolic disturbances linked to oxidative stress and physiological imbalance. Enzymatic activities in gills and liver showed a dynamic response, with elevated catalase (CAT) and superoxide dismutase (SOD) levels at T2 and T3 after 14 days, followed by a decline by day 21. Glutathione S-transferase (GST) activity increased in gills at T2 and T3 after 7 days and in the liver at T3 after 14 days, while lipid peroxidation (LPO) significantly increased in gills at T3 after 7 days and in the liver at T2 and T3 after 14 days. Molecular analysis confirmed upregulation of oxidative stress genes (SOD1, CAT) and inflammatory markers (HSP70, IL- 1β). Histopathological examination revealed gill damage, including lamellar fusion and hyperplasia, and liver degeneration, such as hepatocyte vacuolation and necrosis, with the most severe effects observed at T3. These findings highlight dose-dependent toxicity and oxidative damage caused by the AgNPs-CuONPs mixture, emphasizing its potential physiological and molecular impacts on aquatic organisms.

Point-of-Care-Testing NO3-N Detection Technology with Selected Transition-Metal-Based Colorimetric Sensor Arrays

Nitrate-nitrogen (NO3-N) is a major contaminant in groundwater and seawater. Significant amounts of ammonia are oxidized to nitrate through nitrification, leading to an imbalance in the nitrogen cycle and causing nitrate pollution in water bodies. Controlling NO3-N levels is a significant challenge for both marine aquaculture and human health. Traditional measurement methods, such as ion chromatography and continuous flow analysis, require pretreatment steps to detect NO3-N in complex matrices, which is time-consuming. However, in this study, we developed a transition-metal-based sensor capable of measuring NO3-N concentrations on-site without the need for pretreatment. We analyzed the color change of transition-metal-based sensors over time and obtained color data by mixing transition metals (Mn, V, Fe, Co, Cr, Cu, and Ni) with solvents and additives at fixed ratios, and combining them with standard solutions of NO3-N at concentrations of 1, 2, 3, 5, 10, 20, 30, 40, 50, 75, and 100 ppm. We selected sensors that exhibited linearly increasing color velocity with increasing NO3-N concentrations and developed an array sensor using the selected sensors. The performance of the array was validated by comparing its results with those of hierarchical cluster analysis (HCA) based on color data and compositional analysis, confirming its ability to detect NO3-N in complex matrices. Additionally, by creating a large data set of color change patterns of the array sensor, we can develop selective array sensors for detecting specific substances, surpassing the capability of merely measuring the NO3-N concentration.

Physiological impact of secondary nanoplastics on aquatic inhabitants in special reference to immunotoxicity

Nanoplastic (NP) pollution poses serious health hazards to aquatic ecosystems, impacting various physiological systems of aquatic organisms. This review examines the complex interplay between NPs and different physiological systems. In the digestive system, NPs downregulate the hsp70-like gene in Mytilus galloprovincialis, leading to decreased metabolic processes and impaired digestion. Neural system exposure to NPs induces abnormal expression of genes like neurogenin1, GFAP, FBJ murine osteosarcoma viral oncogene, GAP-43, synapsin IIa, apoptosis regulator a, Bcl2 and Caspase a, and apoptosis-related cysteine peptidase. These genes play a crucial role in neurodevelopment, synaptic function and apoptosis regulation, potentially impacting neurobiology and cancer biology. NPs also affect reproduction, including gametogenesis, spawning, fertilization, embryogenesis and larval survivability. In the respiratory system, treatment with these causes inflammation in the lungs and gills, resulting in respiratory dysfunction. Moreover, this review investigates the complex interaction between NPs and the immune systems of both invertebrates (e.g., molluscs, arthropods, echinoderms) and vertebrates (e.g., zebrafish). NPs-induced alterations in immune cell function heightened the susceptibility to pathogens and disrupted immune signalling pathways. Subcellular inflammatory responses have been characterized by the secretion of inflammation-promoting and chemotactic cytokines such as irg1l, interleukin 1, interferon, interleukin 6, C-C motif chemokine ligand 20a and tumour necrosis factor. The assessment of the combined effects of NPs and other xenobiotics highlighted their possible synergistic impacts on aquatic fauna and the environment. This comprehensive review emphasizes the urgent need for further research to understand the cumulative effects of NPs on organism health and fitness across multiple physiological systems.

Characterization and functional analysis of Litopenaeus vannamei Na+/K+/2Cl- cotransporter 1 under nitrite stress

The function of Litopenaeus vannamei Na+/K+/2Cl- cotransporter 1 (NKCC1) under nitrite stress was investigated. The full-length cDNA sequence of the L. vannamei NKCC1 gene was cloned using the rapid amplification of cDNA ends (RACE) technique, and the sequence was analysed using bioinformatics tools. Expression and localisation of NKCC1 in tissues were assessed using real-time quantitative PCR and in situ hybridisation, respectively. The impact of nitrite stress on the survival, physiology, biochemistry and tissue structure of L. vannamei was investigated following silencing of NKCC1 by RNA interference. The 3143 bp cDNA sequence of L. vannamei NKCC1 encodes a polypeptide of 918 amino acids. It is evolutionarily conserved. NKCC1 expression was highest in gill tissue, particularly within cuticle and gill epithelial cells. After silencing NKCC1, an increase in shrimp survival was observed, accompanied by a significant reduction in nitrite entry into the body (P < 0.05). Moreover, the oxidative stress enzyme system remained unaffected and damage to gill tissue was alleviated. The results suggest that NKCC1 is involved in regulating nitrite uptake, and plays a crucial role in facilitating nitrite entry into the organism through gill tissue. The findings provide a vital experimental basis for addressing concerns related to nitrite toxicity.

Accumulation and elimination properties and comparative toxicity of fluxapyroxad in juvenile and adult large yellow croaker (Larimichthys crocea)

Fluxapyroxad (FX), a succinate dehydrogenase inhibitor fungicide, has been detected in global marine and aquatic organisms. However, as a new pollutant, its biotoxicity and ecological risks to marine aquatic organisms are unclear. The accumulation and elimination processes and toxic effects of FX on Larimichthys crocea (L. crocea) at environmental concentrations were assessed. FX (1.0 μg/L) was rapidly enriched and persisted prolonged in L. crocea muscle and FX is highly toxic to juvenile L. crocea with the 96 h LC50 of 245.0 μg/L. Furthermore, the toxic effects of FX on juvenile L. crocea and adults L. crocea were compared and analyzed. In contrast to those of adult L. crocea, juvenile L. crocea showed a stronger oxidative stress response and rescued liver damage in terms of antioxidant enzyme activity, energy supply, and liver damage to FX. Transcriptomic analysis also showed that drug metabolism was activated. In the adult L. crocea, the disturbance of the energy metabolism, oxidative respiration, TCA cycle, and lipid metabolism genes were firstly found. The results revealed the accumulation and elimination pattern and ecotoxicological hazards of FX to L. crocea, which provided important theoretical basis for the study of environmental risks caused by new pollutants to marine organisms.

Study on the Adaptive Regulation of Light on the Stress Response of Mandarin Fish (Siniperca chuatsi) with Re-Feeding after Starvation

Light influences the stress response to environmental stimuli and feeding behaviors of Siniperca chuatsi and, thus, is an important regulator of normal growth and development. In this study, we first explored the important role of light on the digestive and stress capacity of S. chuatsi by studying the changes in physiological and biochemical indicators of S. chuatsi, taking the re-feeding after starvation as the constant environmental stimulus and the light intensity as the adjustable environmental stimulus. The activity of protease and lipase was generally higher in the stomach tissues than in the intestinal tissues, especially lipase, which was higher in stomach tissues under all light conditions, and the protease and lipase activity peaked in the stomach tissues of S. chuatsi at a light intensity of 18.44 ± 3.00 lx and in intestinal tissues at 11.15 ± 2.01 lx, respectively, indicating that greater light intensity increased the digestive capacity of stomach tissues, whereas lower light intensity facilitated the digestive capacity of intestinal tissues. The tissues of the gill, stomach, and intestine had relatively high activity of stress-related enzymes, whereas the tissues of the brain, kidney, liver, and plasma samples had relatively low activity of enzymes. Collectively, the results show that light intensity at 11.15 ± 2.01 lx promoted digestive capacity in the intestine and enhanced the anti-stress ability of S. chuatsi in response to stress induced by re-feeding after starvation. These findings should prove useful for artificial breeding of S. chuatsi.

Dietary High Glycinin Reduces Growth Performance and Impairs Liver and Intestinal Health Status of Orange-Spotted Grouper (Epinephelus coioides)

The aim of the study was to investigate whether the negative effects of dietary glycinin are linked to the structural integrity damage, apoptosis promotion and microbiota alteration in the intestine of orange-spotted grouper (Epinephelus coioides). The basal diet (FM diet) was formulated to contain 48% protein and 11% lipid. Fish meal was replaced by soybean meal (SBM) in FM diets to prepare the SBM diet. Two experimental diets were prepared, containing 4.5% and 10% glycinin in the FM diets (G-4.5 and G-10, respectively). Triplicate groups of 20 fish in each tank (initial weight: 8.01 ± 0.10 g) were fed the four diets across an 8 week growth trial period. Fish fed SBM diets had reduced growth rate, hepatosomatic index, liver total antioxidant capacity and GSH-Px activity, but elevated liver MDA content vs. FM diets. The G-4.5 exhibited maximum growth and the G-10 exhibited a comparable growth with that of the FM diet group. The SBM and G-10 diets down-regulated intestinal tight junction function genes (occludin, claudin-3 and ZO-1) and intestinal apoptosis genes (caspase-3, caspase-8, caspase-9, bcl-2 and bcl-xL), but elevated blood diamine oxidase activity, D-lactic acid and endotoxin contents related to intestinal mucosal permeability, as well as the number of intestinal apoptosis vs FM diets. The intestinal abundance of phylum Proteobacteria and genus Vibrio in SBM diets were higher than those in groups receiving other diets. As for the expression of intestinal inflammatory factor genes, in SBM and G-10 diets vs. FM diets, pro-inflammatory genes (TNF-α, IL-1β and IL-8) were up-regulated, but anti-inflammatory genes (TGF-β1 and IL-10) were down-regulated. The results indicate that dietary 10% glycinin rather than 4.5% glycinin could decrease hepatic antioxidant ability and destroy both the intestinal microbiota profile and morphological integrity through disrupting the tight junction structure of the intestine, increasing intestinal mucosal permeability and apoptosis. These results further trigger intestinal inflammatory reactions and even enteritis, ultimately leading to the poor growth of fish.