Ammonia nitrogen is the major oxygen-consuming pollutant in aquatic environments. Exposure to ammonia nitrogen in the aquatic environment can lead to bioaccumulation in fish, and the ammonia nitrogen concentration is the main determinant of accumulation. In most aquatic environments, fish are at the top of the food chain and are most vulnerable to the toxic effects of high levels of ammonia nitrogen exposure. In fish exposed to toxicants, ammonia-induced toxicity is mainly caused by bioaccumulation in certain tissues. Ammonia nitrogen absorbed in the fish enters the circulatory system and affects hematological properties. Ammonia nitrogen also breaks balance in antioxidant capacity and causes oxidative damage. In addition, ammonia nitrogen affects the immune response and causes neurotoxicity because of the physical and chemical toxicity. Thence, the purpose of this review was to investigate various toxic effects of ammonia nitrogen, including oxidative stress, neurotoxicity and immune response.

The transport of living fish is an important part of the fish farming process. The transport usually causes fish stress. This study evaluated the effects of transport temperature and vibration frequency on water quality, blood biochemical parameters, gill histomorphology, oxidative stress, and meat quality of pearl gentian groupers after transport. First, 1-year-old groupers (450 ± 25 g) were transported in plastic bags for 48 h, including the following treatments: no shaking, transported at 15 °C, shaking at 70 rpm, transported at 15 °C (15 °C/70 rpm); shaking at 120 rpm, transported at 15 °C (15 °C/120 rpm); no shaking, transported at 25 °C; shaking at 70 rpm, transported at 25 °C (25 °C/70 rpm); and shaking at 120 rpm, transported at 25 °C (25 °C/120 rpm). Serum, liver, gill, and muscle samples were collected for testing at 0, 12, 24, 36, and 48 h of exposure. During the 48 h transport, total ammonia nitrogen (TAN), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX), and malondialdehyde (MDA) were significantly increased in the transport group compared to the control group. In the early stage of transportation, aspartate aminotransferase (AST), alanine aminotransferase (ALT), cortisol (COR), lactate dehydrogenase (LDH), and glucose (GLU) in the transportation groups were significantly higher than those in the control group, while the water quality pH and dissolved oxygen (DO) levels decreased significantly. Compared with untransported fish, the total free amino acid (TFAA) content increased by 40.27% and 31.74% in the 25 °C/70 rpm and 25 °C/120 rpm groups, respectively. In addition, the results of hematoxylin–eosin staining and scanning electron microscopy showed that the epithelial cells in the high-speed group were swollen, the gill lamella was severely curved, and a large amount of mucus was secreted. This study explores the basic information of transportation, which will help to select the conditions that are more suitable for the successful transportation of pearl gentian groupers.

Carvacrol is a natural compound known to be a highly effective antibacterial; however, it is a hydrophobic molecule, which is a limitation to its use within food packaging. Flaxseed gum (FG) films containing different contents of carvacrol (C) were produced by a film-casting method with sonication. The effects of sonication power and time on the properties of the FG-C films were investigated by measuring the film thickness, mechanical properties, contact angle, opacity, water vapor permeability (WVP), water sorption isotherm, Fourier transform infrared spectroscopy(FTIR), differential scanning calorimetry (DSC), antibacterial and antioxidant activities, and microstructure. The results showed that sonication power and time had significant effects on mechanical and barrier properties, film opacity, and degradability (p < 0.05). The tensile strength (TS) and elongation at break (EB) values exhibited an obvious improvement after sonication, and FG-0.5C-6030 had the lowest TS (33.40 MPa) and EB (4.46%) values. FG-C films formed a denser structure and the contact angle was improved as a result of sonication, which improved the integration of carvacrol into the FG matrix. In terms of microstructure, sonication resulted in a homogeneous and continuous crosssection of FG-C films, and regular surface and cross-sectional images were obtained through the highest acoustic intensity and longest time treatment. The FG films incorporated with carvacrol displayed antibacterial properties against Staphylococcus aureus, Vibrio parahaemolyticus, Shewanella putrefaciens, and Pseudomonas fluorescens, as well as increased antioxidant properties, and sonication was proven to enhance both of them.

Ginger (Zingiber officinale) has unique medicinal value and can be used to treat colds and cold-related diseases. The chemical composition and antibacterial activity of ginger essential oil (GEO) against Shewanella putrefaciens were determined in the present study. Zingiberene, α-curcumene, and zingerone were the main active compounds of GEO. GEO displayed significant antibacterial activity against S. putrefaciens, with a minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 2.0 and 4.0 μL/mL, respectively. Changes in intracellular ATP content, nucleic acid and protein structure, exopolysaccharides (EPS) content, and extracellular protease production indicated that GEO disrupted the membrane integrity of S. putrescens. At the same time, changes in biofilm metabolic activity content and the growth curve of biofilm showed that GEO could destroy the biofilm. Both scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) observations confirmed that GEO destroyed the cell membrane and lead to the leakage of the constituents. The above results indicate that GEO entered the cells via contact with bacterial membranes, and then inhibited the growth of S. putrefaciens and its biofilms by increasing membrane permeability and inhibiting various virulence factors such as EPS. The findings showed that GEO could destroy the structure of cell membrane and biofilm of tested S. putrefaciens, indicating its potential as a natural food preservative.

An amino acid analyzer method for the simultaneous determination of 20 free amino acids (FAAs) and glutathione (GSH) in Penaeus vannamei (PV), Penaeus vannamei, Penaeus hidulis (PH) and Penaeus japonicus (PJ) were developed. The effects of different concentrations of trichloroacetic acid (TCA) and ethanol on the extraction of free amino acids were investigated, and 120 g·L⁻¹ TCA was found to be ideal. The target analytes were eluted in sodium citrate buffer B1 (pH = 3.3) containing 135 mL·L⁻¹ ethanol and 1 mol·L⁻¹ sodium hydroxide (7 mL) and at the optimizing conversion time of sodium citrate buffer B2 (pH = 3.2) and sodium citrate buffer B3 (pH = 4.0) of 5.6 min, and the effective separation was achieved within 29.5 min. The developed method showed good linearity (R² ≥ 0.9991) in the range of 1–250 µg·mL⁻¹ with good intra-day and inter-day precision (relative standard deviations ≤ 2.38%) and spike recovery (86.42–103.64%). GSH and cysteine were used to identify marine prawn and freshwater shrimp. Hydroxyproline and serine were used to distinguish PV and Macrobrachium nipponense (MN) from others, respectively. The highest content of the total FAAs was found in PV, and principal component analysis revealed that PV had the highest comprehensive score for FAAs and GSH. Arginine was found to have the greatest influence on shrimp flavor.

This study investigates the changes of the physicochemical characteristics and flavor of fermented Suanyu (Chinese fermented fish) during fermentation with Lactiplantibacillus plantarum (L. plantarum) and Saccharomyces cerevisiae (S. cerevisiae). The related indicators, including pH, water activity (Aw), volatile base nitrogen (TVB-N), thiobarbituric acid (TBA), free amino acids (FAAs), microbial community, and volatile compounds were determined. L. plantarum fermentation samples (LP) and natural fermentation samples (NF) were used as controls. The pH and Aw of three groups of Suanyu samples decreased continuously through the entire fermentation process. Meanwhile, the TVB-N of three groups of samples increased gradually, while TBA first increased and then decreased. Notably, the pH, Aw, TVB-N, and TBA of MF group samples (inoculated L. plantarum and S. cerevisiae) were significantly lower than the NF group samples. In addition, both TVB-N and TBA of the MF group samples were lower than those of the LP group samples during fermentation, suggesting that combined fermentation could inhibit the growth of undesirable microorganisms more effectively. Lactobacillus were the main bacterial genus of the three group fermented samples during fermentation, and combined fermentation could promote the growth of Lactobacillus more significantly. In addition, the highest content of umami (145.16 mg/100 g), sweet amino acids (405.75 mg/100 g), and volatile compounds (especially alcohols and esters) were found in MF group samples, followed by the NF and LP group samples, indicating that combined fermentation could give Suanyu a better flavor quality. This study may provide a theoretical basis for the industrial production of fermented fish products and the improvement of fermentation technology.